From bcfbda98605a9e5c94f472c8b2c8c55ee2585a5c Mon Sep 17 00:00:00 2001 From: Lars Wirzenius Date: Sat, 2 Nov 2019 10:51:03 +0200 Subject: Import historical artifacts --- rhyme.gz | Bin 0 -> 615 bytes sag-0.2.README | 55 + sag-0.2.announcement | 62 + sag-0.2.lsm | 17 + sag-0.2.ps.gz | Bin 0 -> 172489 bytes sag-0.2.tar.gz | Bin 0 -> 86112 bytes sag-0.3-development.tar.gz | Bin 0 -> 320791 bytes sag-0.3.ps.gz | Bin 0 -> 193219 bytes sag-0.6.1-www/Invisible/sag-0.6-ANNOUNCE | 75 + sag-0.6.1-www/Invisible/sag-0.6-html.tar.gz | Bin 0 -> 185920 bytes sag-0.6.1-www/Invisible/sag-0.6-letter.dvi.gz | Bin 0 -> 123697 bytes sag-0.6.1-www/Invisible/sag-0.6-letter.ps.gz | Bin 0 -> 286603 bytes sag-0.6.1-www/Invisible/sag-0.6.tar.gz | Bin 0 -> 109210 bytes sag-0.6.1-www/Invisible/sag-0.6/.ID_MAP.dir | Bin 0 -> 12513 bytes sag-0.6.1-www/Invisible/sag-0.6/.ID_MAP.pag | Bin 0 -> 12513 bytes sag-0.6.1-www/Invisible/sag-0.6/.IMG_PARAMS.dir | Bin 0 -> 12585 bytes sag-0.6.1-www/Invisible/sag-0.6/.IMG_PARAMS.pag | Bin 0 -> 12585 bytes sag-0.6.1-www/Invisible/sag-0.6/.ORIG_MAP.dir | Bin 0 -> 12513 bytes sag-0.6.1-www/Invisible/sag-0.6/.ORIG_MAP.pag | Bin 0 -> 12513 bytes sag-0.6.1-www/Invisible/sag-0.6/blank.pbm | 4 + sag-0.6.1-www/Invisible/sag-0.6/blueball.gif | Bin 0 -> 398 bytes sag-0.6.1-www/Invisible/sag-0.6/change_begin.gif | Bin 0 -> 133 bytes sag-0.6.1-www/Invisible/sag-0.6/change_delete.gif | Bin 0 -> 257 bytes sag-0.6.1-www/Invisible/sag-0.6/change_end.gif | Bin 0 -> 135 bytes sag-0.6.1-www/Invisible/sag-0.6/contents.xbm | 12 + sag-0.6.1-www/Invisible/sag-0.6/contents_motif.gif | Bin 0 -> 225 bytes .../Invisible/sag-0.6/cross_ref_motif.gif | Bin 0 -> 78 bytes sag-0.6.1-www/Invisible/sag-0.6/foot_motif.gif | Bin 0 -> 87 bytes sag-0.6.1-www/Invisible/sag-0.6/footnode.html | 1378 ++++++++++++++++ sag-0.6.1-www/Invisible/sag-0.6/greenball.gif | Bin 0 -> 398 bytes sag-0.6.1-www/Invisible/sag-0.6/icons.html | 42 + sag-0.6.1-www/Invisible/sag-0.6/image.gif | Bin 0 -> 195 bytes sag-0.6.1-www/Invisible/sag-0.6/images.aux | 13 + sag-0.6.1-www/Invisible/sag-0.6/images.bbl | 39 + sag-0.6.1-www/Invisible/sag-0.6/images.idx | 2 + sag-0.6.1-www/Invisible/sag-0.6/images.log | 141 ++ sag-0.6.1-www/Invisible/sag-0.6/images.pl | 36 + sag-0.6.1-www/Invisible/sag-0.6/images.tex | 353 ++++ sag-0.6.1-www/Invisible/sag-0.6/img1.gif | Bin 0 -> 1152 bytes sag-0.6.1-www/Invisible/sag-0.6/img10.gif | Bin 0 -> 1371 bytes sag-0.6.1-www/Invisible/sag-0.6/img11.gif | Bin 0 -> 106 bytes sag-0.6.1-www/Invisible/sag-0.6/img12.gif | Bin 0 -> 1481 bytes sag-0.6.1-www/Invisible/sag-0.6/img13.gif | Bin 0 -> 6652 bytes sag-0.6.1-www/Invisible/sag-0.6/img14.gif | Bin 0 -> 2203 bytes sag-0.6.1-www/Invisible/sag-0.6/img15.gif | Bin 0 -> 3035 bytes sag-0.6.1-www/Invisible/sag-0.6/img2.gif | Bin 0 -> 8450 bytes sag-0.6.1-www/Invisible/sag-0.6/img3.gif | Bin 0 -> 3304 bytes sag-0.6.1-www/Invisible/sag-0.6/img4.gif | Bin 0 -> 5014 bytes sag-0.6.1-www/Invisible/sag-0.6/img5.gif | Bin 0 -> 3072 bytes sag-0.6.1-www/Invisible/sag-0.6/img6.gif | Bin 0 -> 5401 bytes sag-0.6.1-www/Invisible/sag-0.6/img7.gif | Bin 0 -> 1679 bytes sag-0.6.1-www/Invisible/sag-0.6/img8.gif | Bin 0 -> 1683 bytes sag-0.6.1-www/Invisible/sag-0.6/img9.gif | Bin 0 -> 7040 bytes sag-0.6.1-www/Invisible/sag-0.6/index.html | 76 + sag-0.6.1-www/Invisible/sag-0.6/index_motif.gif | Bin 0 -> 180 bytes sag-0.6.1-www/Invisible/sag-0.6/internals.pl | 117 ++ sag-0.6.1-www/Invisible/sag-0.6/invis_anchor.xbm | 4 + sag-0.6.1-www/Invisible/sag-0.6/labels.pl | 117 ++ sag-0.6.1-www/Invisible/sag-0.6/linux-logo.gif | Bin 0 -> 475 bytes sag-0.6.1-www/Invisible/sag-0.6/long-contents.html | 174 ++ sag-0.6.1-www/Invisible/sag-0.6/missfont.log | 1 + .../Invisible/sag-0.6/next_group_motif.gif | Bin 0 -> 259 bytes .../Invisible/sag-0.6/next_group_motif_gr.gif | Bin 0 -> 259 bytes sag-0.6.1-www/Invisible/sag-0.6/next_motif.gif | Bin 0 -> 172 bytes sag-0.6.1-www/Invisible/sag-0.6/next_motif_gr.gif | Bin 0 -> 172 bytes sag-0.6.1-www/Invisible/sag-0.6/node1.html | 22 + sag-0.6.1-www/Invisible/sag-0.6/node10.html | 43 + sag-0.6.1-www/Invisible/sag-0.6/node100.html | 67 + sag-0.6.1-www/Invisible/sag-0.6/node101.html | 93 ++ sag-0.6.1-www/Invisible/sag-0.6/node102.html | 72 + sag-0.6.1-www/Invisible/sag-0.6/node103.html | 101 ++ sag-0.6.1-www/Invisible/sag-0.6/node104.html | 45 + sag-0.6.1-www/Invisible/sag-0.6/node105.html | 57 + sag-0.6.1-www/Invisible/sag-0.6/node106.html | 45 + sag-0.6.1-www/Invisible/sag-0.6/node107.html | 87 + sag-0.6.1-www/Invisible/sag-0.6/node108.html | 56 + sag-0.6.1-www/Invisible/sag-0.6/node109.html | 94 ++ sag-0.6.1-www/Invisible/sag-0.6/node11.html | 39 + sag-0.6.1-www/Invisible/sag-0.6/node110.html | 59 + sag-0.6.1-www/Invisible/sag-0.6/node111.html | 61 + sag-0.6.1-www/Invisible/sag-0.6/node112.html | 107 ++ sag-0.6.1-www/Invisible/sag-0.6/node113.html | 62 + sag-0.6.1-www/Invisible/sag-0.6/node114.html | 789 +++++++++ sag-0.6.1-www/Invisible/sag-0.6/node115.html | 27 + sag-0.6.1-www/Invisible/sag-0.6/node12.html | 47 + sag-0.6.1-www/Invisible/sag-0.6/node13.html | 48 + sag-0.6.1-www/Invisible/sag-0.6/node14.html | 45 + sag-0.6.1-www/Invisible/sag-0.6/node15.html | 45 + sag-0.6.1-www/Invisible/sag-0.6/node16.html | 43 + sag-0.6.1-www/Invisible/sag-0.6/node17.html | 54 + sag-0.6.1-www/Invisible/sag-0.6/node18.html | 47 + sag-0.6.1-www/Invisible/sag-0.6/node19.html | 43 + sag-0.6.1-www/Invisible/sag-0.6/node2.html | 168 ++ sag-0.6.1-www/Invisible/sag-0.6/node20.html | 55 + sag-0.6.1-www/Invisible/sag-0.6/node21.html | 138 ++ sag-0.6.1-www/Invisible/sag-0.6/node22.html | 98 ++ sag-0.6.1-www/Invisible/sag-0.6/node23.html | 153 ++ sag-0.6.1-www/Invisible/sag-0.6/node24.html | 36 + sag-0.6.1-www/Invisible/sag-0.6/node25.html | 73 + sag-0.6.1-www/Invisible/sag-0.6/node26.html | 88 + sag-0.6.1-www/Invisible/sag-0.6/node27.html | 118 ++ sag-0.6.1-www/Invisible/sag-0.6/node28.html | 117 ++ sag-0.6.1-www/Invisible/sag-0.6/node29.html | 83 + sag-0.6.1-www/Invisible/sag-0.6/node3.html | 54 + sag-0.6.1-www/Invisible/sag-0.6/node30.html | 150 ++ sag-0.6.1-www/Invisible/sag-0.6/node31.html | 86 + sag-0.6.1-www/Invisible/sag-0.6/node32.html | 81 + sag-0.6.1-www/Invisible/sag-0.6/node33.html | 40 + sag-0.6.1-www/Invisible/sag-0.6/node34.html | 151 ++ sag-0.6.1-www/Invisible/sag-0.6/node35.html | 51 + sag-0.6.1-www/Invisible/sag-0.6/node36.html | 74 + sag-0.6.1-www/Invisible/sag-0.6/node37.html | 53 + sag-0.6.1-www/Invisible/sag-0.6/node38.html | 45 + sag-0.6.1-www/Invisible/sag-0.6/node39.html | 84 + sag-0.6.1-www/Invisible/sag-0.6/node4.html | 132 ++ sag-0.6.1-www/Invisible/sag-0.6/node40.html | 39 + sag-0.6.1-www/Invisible/sag-0.6/node41.html | 41 + sag-0.6.1-www/Invisible/sag-0.6/node42.html | 91 ++ sag-0.6.1-www/Invisible/sag-0.6/node43.html | 146 ++ sag-0.6.1-www/Invisible/sag-0.6/node44.html | 33 + sag-0.6.1-www/Invisible/sag-0.6/node45.html | 106 ++ sag-0.6.1-www/Invisible/sag-0.6/node46.html | 221 +++ sag-0.6.1-www/Invisible/sag-0.6/node47.html | 86 + sag-0.6.1-www/Invisible/sag-0.6/node48.html | 52 + sag-0.6.1-www/Invisible/sag-0.6/node49.html | 50 + sag-0.6.1-www/Invisible/sag-0.6/node5.html | 61 + sag-0.6.1-www/Invisible/sag-0.6/node50.html | 40 + sag-0.6.1-www/Invisible/sag-0.6/node51.html | 80 + sag-0.6.1-www/Invisible/sag-0.6/node52.html | 61 + sag-0.6.1-www/Invisible/sag-0.6/node53.html | 34 + sag-0.6.1-www/Invisible/sag-0.6/node54.html | 78 + sag-0.6.1-www/Invisible/sag-0.6/node55.html | 51 + sag-0.6.1-www/Invisible/sag-0.6/node56.html | 56 + sag-0.6.1-www/Invisible/sag-0.6/node57.html | 33 + sag-0.6.1-www/Invisible/sag-0.6/node58.html | 48 + sag-0.6.1-www/Invisible/sag-0.6/node59.html | 49 + sag-0.6.1-www/Invisible/sag-0.6/node6.html | 78 + sag-0.6.1-www/Invisible/sag-0.6/node60.html | 69 + sag-0.6.1-www/Invisible/sag-0.6/node61.html | 93 ++ sag-0.6.1-www/Invisible/sag-0.6/node62.html | 104 ++ sag-0.6.1-www/Invisible/sag-0.6/node63.html | 33 + sag-0.6.1-www/Invisible/sag-0.6/node64.html | 111 ++ sag-0.6.1-www/Invisible/sag-0.6/node65.html | 125 ++ sag-0.6.1-www/Invisible/sag-0.6/node66.html | 56 + sag-0.6.1-www/Invisible/sag-0.6/node67.html | 72 + sag-0.6.1-www/Invisible/sag-0.6/node68.html | 224 +++ sag-0.6.1-www/Invisible/sag-0.6/node69.html | 136 ++ sag-0.6.1-www/Invisible/sag-0.6/node7.html | 82 + sag-0.6.1-www/Invisible/sag-0.6/node70.html | 44 + sag-0.6.1-www/Invisible/sag-0.6/node71.html | 35 + sag-0.6.1-www/Invisible/sag-0.6/node72.html | 63 + sag-0.6.1-www/Invisible/sag-0.6/node73.html | 53 + sag-0.6.1-www/Invisible/sag-0.6/node74.html | 74 + sag-0.6.1-www/Invisible/sag-0.6/node75.html | 96 ++ sag-0.6.1-www/Invisible/sag-0.6/node76.html | 80 + sag-0.6.1-www/Invisible/sag-0.6/node77.html | 58 + sag-0.6.1-www/Invisible/sag-0.6/node78.html | 69 + sag-0.6.1-www/Invisible/sag-0.6/node79.html | 46 + sag-0.6.1-www/Invisible/sag-0.6/node8.html | 43 + sag-0.6.1-www/Invisible/sag-0.6/node80.html | 71 + sag-0.6.1-www/Invisible/sag-0.6/node81.html | 75 + sag-0.6.1-www/Invisible/sag-0.6/node82.html | 65 + sag-0.6.1-www/Invisible/sag-0.6/node83.html | 28 + sag-0.6.1-www/Invisible/sag-0.6/node84.html | 70 + sag-0.6.1-www/Invisible/sag-0.6/node85.html | 41 + sag-0.6.1-www/Invisible/sag-0.6/node86.html | 54 + sag-0.6.1-www/Invisible/sag-0.6/node87.html | 45 + sag-0.6.1-www/Invisible/sag-0.6/node88.html | 56 + sag-0.6.1-www/Invisible/sag-0.6/node89.html | 63 + sag-0.6.1-www/Invisible/sag-0.6/node9.html | 65 + sag-0.6.1-www/Invisible/sag-0.6/node90.html | 43 + sag-0.6.1-www/Invisible/sag-0.6/node91.html | 47 + sag-0.6.1-www/Invisible/sag-0.6/node92.html | 76 + sag-0.6.1-www/Invisible/sag-0.6/node93.html | 54 + sag-0.6.1-www/Invisible/sag-0.6/node94.html | 51 + sag-0.6.1-www/Invisible/sag-0.6/node95.html | 70 + sag-0.6.1-www/Invisible/sag-0.6/node96.html | 52 + sag-0.6.1-www/Invisible/sag-0.6/node97.html | 71 + sag-0.6.1-www/Invisible/sag-0.6/node98.html | 76 + sag-0.6.1-www/Invisible/sag-0.6/node99.html | 71 + sag-0.6.1-www/Invisible/sag-0.6/orangeball.gif | Bin 0 -> 398 bytes sag-0.6.1-www/Invisible/sag-0.6/pinkball.gif | Bin 0 -> 398 bytes .../Invisible/sag-0.6/previous_group_motif.gif | Bin 0 -> 303 bytes .../Invisible/sag-0.6/previous_group_motif_gr.gif | Bin 0 -> 303 bytes sag-0.6.1-www/Invisible/sag-0.6/previous_motif.gif | Bin 0 -> 220 bytes .../Invisible/sag-0.6/previous_motif_gr.gif | Bin 0 -> 220 bytes sag-0.6.1-www/Invisible/sag-0.6/purpleball.gif | Bin 0 -> 398 bytes sag-0.6.1-www/Invisible/sag-0.6/redball.gif | Bin 0 -> 398 bytes sag-0.6.1-www/Invisible/sag-0.6/sag.css | 10 + sag-0.6.1-www/Invisible/sag-0.6/sag.html | 76 + sag-0.6.1-www/Invisible/sag-0.6/up_motif.gif | Bin 0 -> 145 bytes sag-0.6.1-www/Invisible/sag-0.6/up_motif_gr.gif | Bin 0 -> 145 bytes sag-0.6.1-www/Invisible/sag-0.6/whiteball.gif | Bin 0 -> 275 bytes sag-0.6.1-www/Invisible/sag-0.6/yellowball.gif | Bin 0 -> 398 bytes sag-0.6.1-www/index.html | 49 + sag-0.6.1-www/sag-0.6.1.html/backup-timeline.gif | Bin 0 -> 1937 bytes sag-0.6.1-www/sag-0.6.1.html/book1.html | 833 ++++++++++ sag-0.6.1-www/sag-0.6.1.html/c1450.html | 264 +++ sag-0.6.1-www/sag-0.6.1.html/c1582.html | 281 ++++ sag-0.6.1-www/sag-0.6.1.html/c1705.html | 387 +++++ sag-0.6.1-www/sag-0.6.1.html/c1905.html | 315 ++++ sag-0.6.1-www/sag-0.6.1.html/c2018.html | 232 +++ sag-0.6.1-www/sag-0.6.1.html/c212.html | 432 +++++ sag-0.6.1-www/sag-0.6.1.html/c2187.html | 318 ++++ sag-0.6.1-www/sag-0.6.1.html/c2432.html | 272 ++++ sag-0.6.1-www/sag-0.6.1.html/c31.html | 337 ++++ sag-0.6.1-www/sag-0.6.1.html/c63.html | 264 +++ sag-0.6.1-www/sag-0.6.1.html/c701.html | 385 +++++ sag-0.6.1-www/sag-0.6.1.html/f23.html | 127 ++ sag-0.6.1-www/sag-0.6.1.html/f26.html | 139 ++ sag-0.6.1-www/sag-0.6.1.html/fstree.gif | Bin 0 -> 2173 bytes sag-0.6.1-www/sag-0.6.1.html/g2516.html | 236 +++ sag-0.6.1-www/sag-0.6.1.html/hd-layout.gif | Bin 0 -> 2877 bytes sag-0.6.1-www/sag-0.6.1.html/hd-mount-mounted.gif | Bin 0 -> 1134 bytes sag-0.6.1-www/sag-0.6.1.html/hd-mount-separate.gif | Bin 0 -> 1163 bytes sag-0.6.1-www/sag-0.6.1.html/hd-schematic.gif | Bin 0 -> 7875 bytes sag-0.6.1-www/sag-0.6.1.html/index.html | 833 ++++++++++ .../sag-0.6.1.html/logins-via-terminals.gif | Bin 0 -> 4152 bytes sag-0.6.1-www/sag-0.6.1.html/overview-kernel.gif | Bin 0 -> 5176 bytes sag-0.6.1-www/sag-0.6.1.html/x1029.html | 1720 ++++++++++++++++++++ sag-0.6.1-www/sag-0.6.1.html/x1366.html | 212 +++ sag-0.6.1-www/sag-0.6.1.html/x1384.html | 460 ++++++ sag-0.6.1-www/sag-0.6.1.html/x1466.html | 290 ++++ sag-0.6.1-www/sag-0.6.1.html/x1495.html | 287 ++++ sag-0.6.1-www/sag-0.6.1.html/x1529.html | 140 ++ sag-0.6.1-www/sag-0.6.1.html/x1532.html | 231 +++ sag-0.6.1-www/sag-0.6.1.html/x1551.html | 308 ++++ sag-0.6.1-www/sag-0.6.1.html/x1602.html | 398 +++++ sag-0.6.1-www/sag-0.6.1.html/x1650.html | 321 ++++ sag-0.6.1-www/sag-0.6.1.html/x1684.html | 164 ++ sag-0.6.1-www/sag-0.6.1.html/x1693.html | 141 ++ sag-0.6.1-www/sag-0.6.1.html/x1697.html | 171 ++ sag-0.6.1-www/sag-0.6.1.html/x1752.html | 402 +++++ sag-0.6.1-www/sag-0.6.1.html/x1812.html | 302 ++++ sag-0.6.1-www/sag-0.6.1.html/x1852.html | 223 +++ sag-0.6.1-www/sag-0.6.1.html/x1880.html | 261 +++ sag-0.6.1-www/sag-0.6.1.html/x1944.html | 199 +++ sag-0.6.1-www/sag-0.6.1.html/x1956.html | 274 ++++ sag-0.6.1-www/sag-0.6.1.html/x1988.html | 137 ++ sag-0.6.1-www/sag-0.6.1.html/x1991.html | 207 +++ sag-0.6.1-www/sag-0.6.1.html/x2008.html | 167 ++ sag-0.6.1-www/sag-0.6.1.html/x2031.html | 537 ++++++ sag-0.6.1-www/sag-0.6.1.html/x2124.html | 248 +++ sag-0.6.1-www/sag-0.6.1.html/x2152.html | 185 +++ sag-0.6.1-www/sag-0.6.1.html/x2166.html | 248 +++ sag-0.6.1-www/sag-0.6.1.html/x2206.html | 178 ++ sag-0.6.1-www/sag-0.6.1.html/x2216.html | 226 +++ sag-0.6.1-www/sag-0.6.1.html/x2240.html | 493 ++++++ sag-0.6.1-www/sag-0.6.1.html/x2315.html | 474 ++++++ sag-0.6.1-www/sag-0.6.1.html/x2405.html | 202 +++ sag-0.6.1-www/sag-0.6.1.html/x2417.html | 220 +++ sag-0.6.1-www/sag-0.6.1.html/x2451.html | 161 ++ sag-0.6.1-www/sag-0.6.1.html/x2457.html | 354 ++++ sag-0.6.1-www/sag-0.6.1.html/x2504.html | 180 ++ sag-0.6.1-www/sag-0.6.1.html/x267.html | 338 ++++ sag-0.6.1-www/sag-0.6.1.html/x338.html | 524 ++++++ sag-0.6.1-www/sag-0.6.1.html/x463.html | 168 ++ sag-0.6.1-www/sag-0.6.1.html/x472.html | 315 ++++ sag-0.6.1-www/sag-0.6.1.html/x531.html | 342 ++++ sag-0.6.1-www/sag-0.6.1.html/x595.html | 425 +++++ sag-0.6.1-www/sag-0.6.1.html/x747.html | 406 +++++ sag-0.6.1-www/sag-0.6.1.html/x787.html | 205 +++ sag-0.6.1-www/sag-0.6.1.html/x801.html | 218 +++ sag-0.6.1-www/sag-0.6.1.html/x811.html | 179 ++ sag-0.6.1-www/sag-0.6.1.html/x817.html | 411 +++++ sag-0.6.1-www/sag-0.6.1.html/x83.html | 189 +++ sag-0.6.1-www/sag-0.6.1.html/x876.html | 812 +++++++++ sag-0.6.1-www/sag-0.6.1.html/x94.html | 687 ++++++++ sag-0.6.1-www/sag-0.6.1.pdf | Bin 0 -> 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The SAG is written using LaTeX, but for the benefit of those +who do not have access to LaTeX, several formatted versions for +different output devices are also provided (I will provide the source, +a .dvi file, and PostScript; I hope I can get someone to do a few +other formats as well, including ASCII). + +I am releasing alpha versions of the SAG for everyone to read, and +especially to comment on. Each alpha version will contain the +chapters that are `finished' so far, and an outline / table of +contents for the rest of the manual. By `finished', I mean that the +chapter contains at least the minimal needed information, that it is +not missing any important (as opposed to merely useful) information, +that I think it is good enough so that I won't get too many mails +about destroyed systems, and that it does not rely on information in +as yet unreleased chapters. + +The alpha versions are not intended to be used for real, so don't +complain if you get in trouble because of them. + +Please send feedback to lars.wirzenius@helsinki.fi but don't be +alarmed if I don't answer very soon. I will be mostly out of touch +with the net until the beginning of September. + +The thing to run through LaTeX is sag.tex. It includes the rest of +the files automatically. + +If you cannot get the other formats, here's a couple of notes on how +to read the LaTeX source: + + A comment is introduced by `%' and continues to the end of a line. + + '{' and '}' are used to delimit groups (as in C, and like + `begin' and `end' in Pascal), and parameters to commands. + + '[' and ']' are also used to delimit parameters to commands. + + A command is introduced by '\' and consists of the next word. + A few of the important commands are \linux (which typesets + Linux in a `nice' way); \cmd{foo}, \fn{foo}, and \man{foo} + which typeset `foo' in a suitable way; and \chapter, \section, + and \subsection, which start the corresponding part in the + book (their argument is the name of the part). You can + probably ignore most other commands. + + If there is something else that looks funny, and doesn't make + sense to be part of the text, you can probably ignore it. + +(I'm not interested in hearing that LaTeX source code is difficult to +read.) diff --git a/sag-0.2.announcement b/sag-0.2.announcement new file mode 100644 index 0000000..37e1d04 --- /dev/null +++ b/sag-0.2.announcement @@ -0,0 +1,62 @@ +Newsgroups: comp.os.linux.announce +From: wirzeniu@cs.helsinki.fi (Lars Wirzenius) +Subject: System Administrators' Guide 0.2 ALPHA +Keywords: LDP, documentation, system administration +Organization: ? +Approved: linux-announce@tc.cornell.edu (Lars Wirzenius) +Followup-to: comp.os.linux.misc + +Just when you thought you were safe... + + The Linux System Administrators' Guide version 0.2 ALPHA + +After a year and a half after the previous version, this version does +not have much proof about time well spent. It mainly sports a number +of smaller spelling fixes, and a rewritten chapter on disks. The +disk chapter is "finished", i.e., it is pitifully inadequate, but at +least it should serve as some sort of introduction to using them under +Linux. I haven't much touched any other stuff, yet. + +This version also has the "Design and Implementation of the Second +Extended Filesystem" paper by Remy Card, Theodore Ts'o, and +Stephen Tweedie, first published in the Proceedings to the First +Dutch International Symposium on Linux, ISBN 90 367 0385 9. Very +well written, it describes inner details ext2fs in a clear and +easily understandable way. (Such understanding can be very valuable +when having problems.) + +An "LDP Rhyme", by an anonymous author, is also included. + +A postscript file (about 600 kilobytes uncompressed) is provided. +I know of no tools to create a good plain text version from LaTeX +source, so I'm again missing one. The deTeX command (e.g., ftp.funet.fi, +utils/TeX) can be used to get somewhat readable output, but it would +require way too much hand editing for me to do it. The text is +exactly 100 pages (using my formatting options), if you are thinking +about printing it out. + +Begin3 +Title: Linux System Administrators' Guide +Version: 0.2 +Entered-date: 04FEB95 +Description: An ALPHA version ("trust this and die") of the Linux + Systems Administrators' Guide, one of the Linux + Documentation Project books. +Keywords: LDP, documentation, System Administrators' Guide +Author: wirzeniu@cs.helsinki.fi (Lars Wirzenius) +Maintained-by: wirzeniu@cs.helsinki.fi (Lars Wirzenius) +Primary-site: sunsite.unc.edu /pub/Linux/docs/LDP/ + sag-0.2.tar.gz + sag-0.2.ps.gz +Platforms: Requires LaTeX2e for typesetting; a postscript file is + included. +Copying-policy: LDP +End + +-- +Lars.Wirzenius@helsinki.fi (finger wirzeniu@klaava.helsinki.fi) +Publib version 0.4: ftp://ftp.cs.helsinki.fi/pub/Software/Local/Publib/ + +-- +Send submissions for comp.os.linux.announce to: linux-announce@news.ornl.gov +PLEASE remember Keywords: and a short description of the software. diff --git a/sag-0.2.lsm b/sag-0.2.lsm new file mode 100644 index 0000000..0d6e031 --- /dev/null +++ b/sag-0.2.lsm @@ -0,0 +1,17 @@ +Begin3 +Title: Linux System Administrators' Guide +Version: 0.2 +Entered-date: 04FEB95 +Description: An ALPHA version ("trust this and die") of the Linux + Systems Administrators' Guide, one of the Linux + Documentation Project books. +Keywords: LDP, documentation, System Administrators' Guide +Author: wirzeniu@cs.helsinki.fi (Lars Wirzenius) +Maintained-by: wirzeniu@cs.helsinki.fi (Lars Wirzenius) +Primary-site: sunsite.unc.edu /pub/Linux/docs/LDP/ + sag-0.2.tar.gz + sag-0.2.ps.gz +Platforms: Requires LaTeX2e for typesetting; a postscript file is + included. +Copying-policy: LDP +End diff --git a/sag-0.2.ps.gz b/sag-0.2.ps.gz new file mode 100644 index 0000000..c4e4bfd Binary files /dev/null and b/sag-0.2.ps.gz differ diff --git a/sag-0.2.tar.gz b/sag-0.2.tar.gz new file mode 100644 index 0000000..8a2f1b6 Binary files /dev/null and b/sag-0.2.tar.gz differ diff --git a/sag-0.3-development.tar.gz b/sag-0.3-development.tar.gz new file mode 100644 index 0000000..9abca40 Binary files /dev/null and b/sag-0.3-development.tar.gz differ diff --git a/sag-0.3.ps.gz b/sag-0.3.ps.gz new file mode 100644 index 0000000..2b995b9 Binary files /dev/null and b/sag-0.3.ps.gz differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6-ANNOUNCE b/sag-0.6.1-www/Invisible/sag-0.6-ANNOUNCE new file mode 100644 index 0000000..a7a4643 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6-ANNOUNCE @@ -0,0 +1,75 @@ +Lars Wirzenius + loudly resents + + a Linux Documentation Project + production + + of the least selling book + by the same name + + the Linux System Administrators' Guide 0.6 + just when you thought your system was safe + + starring Super User as Mr. Root + + introducing Lasu as Luser + + special effects by Don Knuth and Leslie Lamport + + music by Crash and Burn + + coming soon to an + ftp://sunsite.unc.edu/pub/Linux/docs/LDP/sysadmin-guide/ near you + + + +Yes, it's that time of the year again, when Lasu thinks he's an +author! The new version features several new spelling errors for readers +to report, a brand new chapter on init, and an announcement text ripped +of an earlier one. Get your copy today, while the supplies last! Two for +the price of one! No system crash is complete without the SAG! + + + -x-X-x- + +Table of contents: + + * Introduction + * Overview of a Linux System + * Overview of the Directory Tree + * Using Disks and Other Storage Media + * Allocating disk space + * Memory Management + * Boots And Shutdowns + * init + * Logging In And Out + * Managing user accounts + * Backups + * Keeping Time + * Measuring Holes + * Glossary (DRAFT) + * References + * Index + +The files are: + + sag-0.6.tar.gz source code (no formatted versions) + sag-0.6-html.tar.gz HTML + sag-0.6-letter.ps.gz Postscript for letter paper + sag-0.6-letter.dvi.gz DVI for letter apper (no figures) + +Most people will probably only need to download the PS version. +It is all you need if you have a PS printer. And happen to use +letter size paper (200 million Americans can't be wrong). + +No text version is available, I do not have the time to produce +one. Don't ask me to. (I'll make one for 1.0.) + +The SAG home page is still at . +All the files are there, including an unpacked, browsable version of +the HTML version. + +As usual, feedback is more than welcome. + +I plan to to call the next version 1.0. It'll follow the grand tradition +of version 1.0 being _almost_ useful, but still crashing your system. :) diff --git a/sag-0.6.1-www/Invisible/sag-0.6-html.tar.gz b/sag-0.6.1-www/Invisible/sag-0.6-html.tar.gz new file mode 100644 index 0000000..f0e0c44 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6-html.tar.gz differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6-letter.dvi.gz b/sag-0.6.1-www/Invisible/sag-0.6-letter.dvi.gz new file mode 100644 index 0000000..ef0d585 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6-letter.dvi.gz differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6-letter.ps.gz b/sag-0.6.1-www/Invisible/sag-0.6-letter.ps.gz new file mode 100644 index 0000000..7adc5ae Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6-letter.ps.gz differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6.tar.gz b/sag-0.6.1-www/Invisible/sag-0.6.tar.gz new file mode 100644 index 0000000..d003679 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6.tar.gz differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/.ID_MAP.dir b/sag-0.6.1-www/Invisible/sag-0.6/.ID_MAP.dir new file mode 100755 index 0000000..d7cde34 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/.ID_MAP.dir differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/.ID_MAP.pag b/sag-0.6.1-www/Invisible/sag-0.6/.ID_MAP.pag new file mode 100755 index 0000000..d7cde34 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/.ID_MAP.pag differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/.IMG_PARAMS.dir b/sag-0.6.1-www/Invisible/sag-0.6/.IMG_PARAMS.dir new file mode 100755 index 0000000..58a9ee1 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/.IMG_PARAMS.dir differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/.IMG_PARAMS.pag b/sag-0.6.1-www/Invisible/sag-0.6/.IMG_PARAMS.pag new file mode 100755 index 0000000..58a9ee1 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/.IMG_PARAMS.pag differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/.ORIG_MAP.dir b/sag-0.6.1-www/Invisible/sag-0.6/.ORIG_MAP.dir new file mode 100755 index 0000000..95e4c00 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/.ORIG_MAP.dir differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/.ORIG_MAP.pag b/sag-0.6.1-www/Invisible/sag-0.6/.ORIG_MAP.pag new file mode 100755 index 0000000..95e4c00 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/.ORIG_MAP.pag differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/blank.pbm b/sag-0.6.1-www/Invisible/sag-0.6/blank.pbm new file mode 100644 index 0000000..3c72463 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/blank.pbm @@ -0,0 +1,4 @@ +P4 +# CREATOR: XV Version 3.00 Rev: 3/30/93 +1 1 + \ No newline at end of file diff --git a/sag-0.6.1-www/Invisible/sag-0.6/blueball.gif b/sag-0.6.1-www/Invisible/sag-0.6/blueball.gif new file mode 100644 index 0000000..c481395 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/blueball.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/change_begin.gif b/sag-0.6.1-www/Invisible/sag-0.6/change_begin.gif new file mode 100644 index 0000000..dbe8d7e Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/change_begin.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/change_delete.gif b/sag-0.6.1-www/Invisible/sag-0.6/change_delete.gif new file mode 100644 index 0000000..63398f5 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/change_delete.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/change_end.gif b/sag-0.6.1-www/Invisible/sag-0.6/change_end.gif new file mode 100644 index 0000000..8f1e455 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/change_end.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/contents.xbm b/sag-0.6.1-www/Invisible/sag-0.6/contents.xbm new file mode 100644 index 0000000..a3aed9f --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/contents.xbm @@ -0,0 +1,12 @@ +#define contents_width 63 +#define contents_height 16 +static char contents_bits[] = { + 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, + 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, + 0x00,0x00,0xc0,0x01,0x00,0x08,0x00,0x00,0x01,0x00,0x20,0x02,0x00,0x08,0x00, + 0x00,0x01,0x00,0x20,0xe2,0x74,0x7c,0x9c,0x8e,0x8f,0x03,0x20,0x10,0x99,0x08, + 0x22,0x13,0x41,0x04,0x20,0x10,0x89,0x08,0x3e,0x11,0x81,0x03,0x20,0x12,0x89, + 0x08,0x02,0x11,0x01,0x04,0x20,0x12,0x89,0x88,0x22,0x11,0x51,0x04,0xc0,0xe1, + 0x9c,0x71,0x9c,0x33,0x8e,0x03,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, + 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, + 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00}; diff --git a/sag-0.6.1-www/Invisible/sag-0.6/contents_motif.gif b/sag-0.6.1-www/Invisible/sag-0.6/contents_motif.gif new file mode 100644 index 0000000..7b3c904 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/contents_motif.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/cross_ref_motif.gif b/sag-0.6.1-www/Invisible/sag-0.6/cross_ref_motif.gif new file mode 100644 index 0000000..4c074e1 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/cross_ref_motif.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/foot_motif.gif b/sag-0.6.1-www/Invisible/sag-0.6/foot_motif.gif new file mode 100644 index 0000000..f29222a Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/foot_motif.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/footnode.html b/sag-0.6.1-www/Invisible/sag-0.6/footnode.html new file mode 100644 index 0000000..a0226cf --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/footnode.html @@ -0,0 +1,1378 @@ + + + + +Footnotes + + + + + + + +
...simple.
There are some people who do + call it that, but that's just because they have never + read this manual, poor things. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...chapter.
If you happen to be reading a version that + has a chapter on backups, that is. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...work
A comparison between the xia and ext2 + filesystems, the device list and a description of the + ext2 filesystem. These aren't part of the book any + more. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...Rhyme
The author + wishes to remain anonymous. It was posted to the + LDP mailing list by Matt Welsh. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
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+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...system
In fact, it is often mistakenly considered to be the + operating system itself, but it is not. An operating system + provides many more services than a plain kernel. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...these
Well, at least + there can be many. Network bandwidth still being a scarce + resource, there is still some practical upper limit to the + number of concurrent logins via one network connection. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
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+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...printer.
Instead, + they form a new queue at the printer, waiting for their + printouts, since no one ever seems to be able to get the queue + software to know exactly when anyone's printout is really finished. + This is a great boost to intra-office social relations. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...platters,
The platters are made of + a hard substance, e.g., aluminium, which gives the hard disk its + name. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...BIOS
The BIOS is some built-in software + stored on ROM chips. It takes care, among other things, of the + initial stages of booting. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...track
The numbers are + completely imaginary. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...disk
That is, the surface inside the disk, on the + metal disk inside the plastic coating. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...similar
But completely + different, of course. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...primary
Illogical? +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...everyone.
It requires several seconds of hard + thinking on the users' behalf. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...magic.
For more + information, see the kernel source or the Kernel Hackers' + Guide. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...NAME="1651">
It should of course be + unmount , but the n mysteriously disappeared in + the 70's, and hasn't been seen since. Please return it to Bell + Labs, NJ, if you find it. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...disk.
Sic transit discus mundi. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...anyway.
Thus quite needlessly + annoying a number of computer scientists something horrible. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...2 GB.
A gigabyte here, a gigabyte there, pretty soon + we start talking about real memory. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...disk
Except a RAM disk, for obvious + reasons. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...loaded
On early computers, it wasn't enough + to merely turn on the computer, you had to manually load the + operating system as well. These new-fangled thing-a-ma-jigs do + it all by themselves. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...right,
This is called + the power on self test, or POST for short. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...NAME="2155">
sync  flushes the buffer cache. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...graphs.
init  itself is not allowed + to die. You can't kill init  even with SIGKILL. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...signal;
Using the command + kill -HUP 1  as root, for example +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...terminal.
Different versions + of getty  are run differently. Consult your manual page-and + make sure it is the correct manual page. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...emergency.
Kernel + command line arguments can be given via LILO, for example. See + section 7.5. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...location.
Or to start nethack . +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...tasks,
It probably shouldn't be used for playing + nethack . +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...it.
Good Linux distributions do this out + of the box. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...microcomputers.
It might be quite embarrassing + if my sister could read my love letters. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...password.
Yes, this means + that the password file has all the information about a + user except his password. The wonder of development. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...accounts
Surreal users? +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...alias.
The + user's name might change due to marriage, for example, and + he might want to have his username reflect his new name. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...work.
But they can be so fun, if you're + a BOFH. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...disasters.
The fifth reason is ``something else''. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...work.
Don't laugh. This has happened to several people. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...work.
Been there, done that... +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...reinstalled,
You get + to decide what's easy. Some people consider installing from + dozens of floppies easy. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...drive.
If a tape + drive doesn't data fast enough, it has to stop; this makes backups + even slower, and can be bad for the tape and the drive. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...round,
According to + recent research. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
...time.
Beware of the time  command, which does + not show the current time. +
.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+.
+
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/greenball.gif b/sag-0.6.1-www/Invisible/sag-0.6/greenball.gif new file mode 100644 index 0000000..2ffbb22 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/greenball.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/icons.html b/sag-0.6.1-www/Invisible/sag-0.6/icons.html new file mode 100644 index 0000000..d6b38c3 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/icons.html @@ -0,0 +1,42 @@ + +
+ +

+ +

+ +

+ +

+ +

+ +

+ +

+ +

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+ +

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+ +

+ + +

+ + + + + + +

+ +changeend

+ +

changeend diff --git a/sag-0.6.1-www/Invisible/sag-0.6/image.gif b/sag-0.6.1-www/Invisible/sag-0.6/image.gif new file mode 100644 index 0000000..7e6cb1a Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/image.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/images.aux b/sag-0.6.1-www/Invisible/sag-0.6/images.aux new file mode 100644 index 0000000..8f6adaa --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/images.aux @@ -0,0 +1,13 @@ +\relax +\newlabel{fig:kernel-overview}{{}{2}} +\newlabel{fig:fstree}{{}{3}} +\newlabel{fig:hd-schematic}{{}{4}} +\newlabel{fig:hard-disk-layout}{{}{5}} +\newlabel{tab:partition-ids}{{}{6}} +\newlabel{fig:hd-mount-root}{{}{7}} +\newlabel{fig:hd-mount-all}{{}{8}} +\newlabel{fig:dumpe2fs-output}{{}{9}} +\newlabel{tab:run-levels}{{}{12}} +\newlabel{fig:terminal-logins}{{}{13}} +\newlabel{fig:backup-history-timeline}{{}{14}} +\newlabel{tab:efficient-backup-levels}{{}{15}} diff --git a/sag-0.6.1-www/Invisible/sag-0.6/images.bbl b/sag-0.6.1-www/Invisible/sag-0.6/images.bbl new file mode 100644 index 0000000..678c847 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/images.bbl @@ -0,0 +1,39 @@ +\begin{thebibliography}{Qui95} + +\bibitem[Anv]{device-list} +Peter Anvin. +\newblock Linux device list. +\newblock A list of major and minor device numbers for Linux devices. \ Now + included in the kernel sources. + +\bibitem[Cha]{bootdisk-howto} +Graham Chapman. +\newblock Bootdisk howto. +\newblock Available with other Linux HOWTO's. + +\bibitem[Kir]{network-admin-guide} +Olaf Kirch. +\newblock Linux network administrators' guide. + +\bibitem[Qui95]{fsstnd-1.2} +Daniel Quinlan. +\newblock {\em Linux Filesystem Structure---Release 1.2}, March 1995. +\newblock A description of and a proposal for a standard Linux directory tree, + with the intention is to make it easier to package software and administer + Linux systems by making files appear in standard places. Follows fairly + closely traditional Unix practice, and has got support from most Linux + distributions. Available via FTP from \texttt{ftp.funet.fi}, directory + \texttt{/pub/Linux/doc/fsstnd}. + +\bibitem[TV]{ext2-defrag} +Stephen Tweedie and Alexei Vovenko. +\newblock Linux filesystem defragmenter. +\newblock Available electronically from \ + \texttt{ftp://sunsite.unc.edu/pub/Linux/system/Filesystems/defrag-0.6.tar.gz% +}. + +\bibitem[Wel]{getting-started} +Matt Welsh. +\newblock Installation and getting started guide. + +\end{thebibliography} diff --git a/sag-0.6.1-www/Invisible/sag-0.6/images.idx b/sag-0.6.1-www/Invisible/sag-0.6/images.idx new file mode 100644 index 0000000..df0a2d5 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/images.idx @@ -0,0 +1,2 @@ +\indexentry{/usr}{10} +\indexentry{/home}{10} diff --git a/sag-0.6.1-www/Invisible/sag-0.6/images.log b/sag-0.6.1-www/Invisible/sag-0.6/images.log new file mode 100644 index 0000000..4a58761 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/images.log @@ -0,0 +1,141 @@ +This is TeX, Version 3.14159 (C version 6.1) (format=latex 97.5.30) 15 NOV 1997 02:32 +**./images.tex +(images.tex +LaTeX2e <1996/12/01> +Babel and hyphenation patterns for american, german, loaded. + +(/usr/lib/texmf/tex/latex/base/report.cls +Document Class: report 1996/10/31 v1.3u Standard LaTeX document class +(/usr/lib/texmf/tex/latex/base/size10.clo +File: size10.clo 1996/10/31 v1.3u Standard LaTeX file (size option) +) +\c@part=\count79 +\c@chapter=\count80 +\c@section=\count81 +\c@subsection=\count82 +\c@subsubsection=\count83 +\c@paragraph=\count84 +\c@subparagraph=\count85 +\c@figure=\count86 +\c@table=\count87 +\abovecaptionskip=\skip41 +\belowcaptionskip=\skip42 +\bibindent=\dimen102 +) (../linuxdoc.sty +Linux Documentation Style `linuxdoc', version 0.40 <7 Oct 93> +) (/usr/lib/texmf/tex/latex/graphics/graphics.sty +Package: graphics 1996/10/31 v1.0c Standard LaTeX Graphics (DPC,SPQR) +(/usr/lib/texmf/tex/latex/graphics/trig.sty +Package: trig 1994/10/16 v1.08 sin cos tan (DPC) +) (/usr/lib/texmf/tex/latex/config/graphics.cfg) +Package graphics Info: Driver file: dvips.def on input line 82. +(/usr/lib/texmf/tex/latex/graphics/dvips.def +File: dvips.def 1996/12/12 v3.0d Driver-dependant file (DPC,SPQR) +)) (/usr/lib/texmf/tex/latex/base/makeidx.sty +Package: makeidx 1995/04/19 v1.0j Standard LaTeX package +) (/usr/lib/texmf/tex/latex/base/t1enc.sty +Package: t1enc 1994/06/01 Standard LaTeX package +) +\@indexfile=\write3 +Writing index file images.idx +\lthtmlwrite=\write4 +\sizebox=\box26 +(images.aux) +LaTeX Font Info: Checking defaults for OML/cmm/m/it on input line 45. +LaTeX Font Info: ... okay on input line 45. +LaTeX Font Info: Checking defaults for T1/cmr/m/n on input line 45. +LaTeX Font Info: ... okay on input line 45. +LaTeX Font Info: Checking defaults for OT1/cmr/m/n on input line 45. +LaTeX Font Info: ... okay on input line 45. +LaTeX Font Info: Checking defaults for OMS/cmsy/m/n on input line 45. +LaTeX Font Info: ... okay on input line 45. +LaTeX Font Info: Checking defaults for OMX/cmex/m/n on input line 45. +LaTeX Font Info: ... okay on input line 45. +LaTeX Font Info: Checking defaults for U/cmr/m/n on input line 45. +LaTeX Font Info: ... okay on input line 45. +File: linux-logo.ps Graphic file (type eps) + +Runaway argument? +! Paragraph ended before \setcounter was complete. + + \par +l.52 + +I suspect you've forgotten a `}', causing me to apply this +control sequence to too much text. How can we recover? +My plan is to forget the whole thing and hope for the best. + +[1 + + +] +File: overview/overview-kernel.ps Graphic file (type eps) + [2 + +] +File: walkabout/fstree.ps Graphic file (type eps) + [3 + +] +File: disks/hd-schematic.ps Graphic file (type eps) + [4 + +] +File: disks/hd-layout.ps Graphic file (type eps) + [5 + +] +LaTeX Font Info: External font `cmex10' loaded for size +(Font) <7> on input line 128. +LaTeX Font Info: External font `cmex10' loaded for size +(Font) <5> on input line 128. +[6 + +] +File: disks/hd-mount-separate.ps Graphic file (type eps) + [7 + +] +File: disks/hd-mount-mounted.ps Graphic file (type eps) + [8 + +] +LaTeX Font Info: Try loading font information for T1+cmtt on input line 182. + +(/usr/lib/texmf/tex/latex/base/t1cmtt.fd +File: t1cmtt.fd 1997/01/14 v2.5a Standard LaTeX font definitions +) [9 + +] [10 + +] +latex2htmlSize :tex2html_wrap_inline4269: 7.5pt::2.5pt. +[11 + +] [12 + +] +File: logins/logins-via-terminals.ps Graphic file (type eps) + [13 + +] +File: backups/backup-timeline.ps Graphic file (type eps) + [14 + +] [15 + +] (images.aux) + +LaTeX Warning: Label(s) may have changed. Rerun to get cross-references right. + + ) +Here is how much of TeX's memory you used: + 639 strings out of 10907 + 6846 string characters out of 72326 + 51228 words of memory out of 262141 + 3493 multiletter control sequences out of 9500 + 5794 words of font info for 18 fonts, out of 150000 for 255 + 14 hyphenation exceptions out of 607 + 23i,8n,18p,219b,451s stack positions out of 300i,40n,60p,3000b,4000s + +Output written on images.dvi (15 pages, 5432 bytes). diff --git a/sag-0.6.1-www/Invisible/sag-0.6/images.pl b/sag-0.6.1-www/Invisible/sag-0.6/images.pl new file mode 100644 index 0000000..2e9fb5d --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/images.pl @@ -0,0 +1,36 @@ +# LaTeX2HTML 96.1-h (September 30, 1996) +# Associate images original text with physical files. + +$key = q/{figure}[htb]centerincludegraphicsoverviewoverview-kernel.pscenterlabelfig:kernel-overview{figure}/; +$cached_env_img{$key} = q|figure147|; +$key = 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+\def\lthtmltypeout#1{{\let\protect\string\immediate\write\lthtmlwrite{#1}}}% +\newbox\sizebox +\textheight 50cm +\begin{document} +\pagestyle{empty} +{\newpage\clearpage\samepage +\includegraphics{linux-logo.ps}}\hbox{}\vfil + + +\setcounter{tocdepth}% + +\stepcounter{chapter} +\stepcounter{chapter} +\stepcounter{section} +\stepcounter{section} +{\newpage\clearpage\samepage +\begin{figure}[htb] +\begin{center} +\includegraphics{overview/overview-kernel.ps} +\end{center} + +\label{fig:kernel-overview} +\end{figure}}\hbox{}\vfil + +\stepcounter{section} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{section} +\stepcounter{chapter} +\stepcounter{section} +{\newpage\clearpage\samepage +\begin{figure}[htb] + \begin{center} + \includegraphics{walkabout/fstree.ps} + \end{center} + + \label{fig:fstree} + \end{figure}}\hbox{}\vfil + +\stepcounter{section} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{chapter} +\stepcounter{section} +\stepcounter{section} +{\newpage\clearpage\samepage +\begin{figure}[thb] + \begin{center} + \includegraphics{disks/hd-schematic.ps} + \end{center} + + \label{fig:hd-schematic} + \end{figure}}\hbox{}\vfil + +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{subsection} +\stepcounter{subsection} +{\newpage\clearpage\samepage +\begin{figure}[thb] + \begin{center} + \includegraphics{disks/hd-layout.ps} + \end{center} + + \label{fig:hard-disk-layout} + \end{figure}}\hbox{}\vfil + +\stepcounter{subsection} +{\newpage\clearpage\samepage +\begin{table}[ht] + +\begin{center} +\begin{tabular}{rl rl rl rl} +\hline +0 & Empty & 40 & Venix 80286 & 94 & Amoeba BBT \\ +1 & DOS 12-bit FAT & 51 & Novell? & a5 & BSD/386 \\ +2 & XENIX root & 52 & Microport & b7 & BSDI fs \\ +3 & XENIX usr & 63 & GNU HURD & b8 & BSDI swap \\ +4 & DOS 16-bit $<$32M & 64 & Novell & c7 & Syrinx \\ +5 & Extended & 75 & PC/IX & db & CP/M \\ +6 & DOS 16-bit $\ge$32M & 80 & Old MINIX & e1 & DOS access \\ +7 & OS/2 HPFS & 81 & Linux/MINIX & e3 & DOS R/O \\ +8 & AIX & 82 & Linux swap & f2 & DOS secondary \\ +9 & AIX bootable & 83 & Linux native & ff & BBT \\ +a & OS/2 Boot Manag & 93 & Amoeba & & \\ +\hline +\end{tabular} +\end{center} +\label{tab:partition-ids} +\end{table}}\hbox{}\vfil + +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{section} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +{\newpage\clearpage\samepage +\begin{figure}[thb] + \begin{center} + \includegraphics{disks/hd-mount-separate.ps} + \end{center} + + \label{fig:hd-mount-root} + \end{figure}}\hbox{}\vfil + +{\newpage\clearpage\samepage +\begin{figure}[thb] + \begin{center} + \includegraphics{disks/hd-mount-mounted.ps} + \end{center} + + \label{fig:hd-mount-all} + \end{figure}}\hbox{}\vfil + +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +{\newpage\clearpage\samepage +\begin{figure}[t] +\begin{center} +\small +\begin{verbatim}dumpe2fs 0.5b, 11-Mar-95 for EXT2 FS 0.5a, 94/10/23 +Filesystem magic number: 0xEF53 +Filesystem state: clean +Errors behavior: Continue +Inode count: 360 +Block count: 1440 +Reserved block count: 72 +Free blocks: 1133 +Free inodes: 326 +First block: 1 +Block size: 1024 +Fragment size: 1024 +Blocks per group: 8192 +Fragments per group: 8192 +Inodes per group: 360 +Last mount time: Tue Aug 8 01:52:52 1995 +Last write time: Tue Aug 8 01:53:28 1995 +Mount count: 3 +Maximum mount count: 20 +Last checked: Tue Aug 8 01:06:31 1995 +Check interval: 0 +Reserved blocks uid: 0 (user root) +Reserved blocks gid: 0 (group root) + +Group 0: + Block bitmap at 3, Inode bitmap at 4, Inode table at 5 + 1133 free blocks, 326 free inodes, 2 directories + Free blocks: 307-1439 + Free inodes: 35-360\end{verbatim} +\end{center} + +\label{fig:dumpe2fs-output} +\end{figure}}\hbox{}\vfil + +\stepcounter{section} +\stepcounter{section} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +{\newpage\clearpage\samepage +\begin{tabular}{r l} + 5 MB & root filesystem \\ + 10 MB & swap partition \\ + 180 MB & \texttt{/usr}\index{/usr} filesystem \\ + 120 MB & \texttt{/home}\index{/home} filesystem \\ + 15 MB & scratch partition + \end{tabular}}\hbox{}\vfil + +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{chapter} +\stepcounter{section} +\stepcounter{section} +{\newpage\clearpage\samepage +\setbox\sizebox=\hbox{$(4096-10)\times 8\times 4096 = 133890048$}\lthtmltypeout{latex2htmlSize :tex2html_wrap_inline4269: \the\ht\sizebox::\the\dp\sizebox.}\box\sizebox}\hbox{}\vfil + +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{chapter} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{chapter} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +{\newpage\clearpage\samepage +\begin{table}[h] + + \label{tab:run-levels} + \begin{center} + \begin{tabular}{ll} + \hline + 0 & Halt the system. \\ + 1 & Single-user mode (for special administration). \\ + 2--5 & Normal operation (user defined). \\ + 6 & Reboot. \\ + \hline + \end{tabular} + \end{center} + \end{table}}\hbox{}\vfil + +\stepcounter{section} +\stepcounter{section} +\stepcounter{chapter} +\stepcounter{section} +{\newpage\clearpage\samepage +\begin{figure}[htb] +\begin{center} +\includegraphics{logins/logins-via-terminals.ps} +\end{center} + +\label{fig:terminal-logins} +\end{figure}}\hbox{}\vfil + +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{chapter} +\stepcounter{section} +\stepcounter{section} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{chapter} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{section} +\stepcounter{subsection} +\stepcounter{subsection} +\stepcounter{section} +{\newpage\clearpage\samepage +\begin{figure}[t] + \begin{center} + \includegraphics{backups/backup-timeline.ps} + \end{center} + + \label{fig:backup-history-timeline} + \end{figure}}\hbox{}\vfil + +{\newpage\clearpage\samepage +\begin{figure}[htb] + +\label{tab:efficient-backup-levels} +\begin{center} +\begin{tabular}{r l l l} +Tape & Level & Backup& Restore \\ +& & (days)& tapes \\ +\hline +1 & 0 & n/a & 1 \\ +2 & 3 & 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a/sag-0.6.1-www/Invisible/sag-0.6/index.html b/sag-0.6.1-www/Invisible/sag-0.6/index.html new file mode 100644 index 0000000..d39d103 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/index.html @@ -0,0 +1,76 @@ + + + + + +Linux System Administrators' Guide 0.6 + + + + + + + + + +

Linux System Administrators' Guide 0.6

+ +

Lars Wirzenius + +

[Linux logo] +The Linux Documentation Project + +

This is version 0.6 of the Linux System Administrators' Guide.
+Published November 15, 1997. + +

+ +Contents + +
+ +

The LaTeX source code and other machine readable formats +can be found on the Internet via anonymous ftp on +sunsite.unc.edu, +in the directory /pub/Linux/docs/LDP. +Also available are at least Postscript and TeX .DVI formats. +The official home page for the book is +\texttt{http://www.iki.fi/liw/linux/sag/}. The current version can always +be found at that location. + +

Copyright © 1993-1997 Lars Wirzenius. + +

Trademarks are owned by their owners. + +

Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +

Permission is granted to process the document source code +through TeX or other formatters and print the +results, and distribute the printed document, +provided the printed document carries copying permission +notice identical to this one, including the references to where +the source code can be found and the official home page. + +

Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided that the entire +resulting derived work is distributed under the terms of a permission +notice identical to this one. + +

Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions. + +

The author would appreciate a notification of modifications, translations, +and printed versions. Thank you. + +

+

+ +

This page is dedicated to a future dedication. + +

In the mean time...I'd like someone who knows him let Terry +Pratchett know that his way of using footnotes is rather inspiring. + + + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/index_motif.gif b/sag-0.6.1-www/Invisible/sag-0.6/index_motif.gif new file mode 100644 index 0000000..b9b3108 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/index_motif.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/internals.pl b/sag-0.6.1-www/Invisible/sag-0.6/internals.pl new file mode 100644 index 0000000..b09dd03 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/internals.pl @@ -0,0 +1,117 @@ +# LaTeX2HTML 96.1-h (September 30, 1996) +# Associate internals original text with physical files. + +$key = q/secswapalloc/; +$ref_files{$key} = "$dir".q|node64.html|; +$noresave{$key} = "$nosave"; +$key = q/secsingleusermode/; +$ref_files{$key} = "$dir".q|node78.html|; +$noresave{$key} = "$nosave"; +$key = q/cite_bootdisk-howto/; +$ref_files{$key} = "$dir".q|node113.html|; +$noresave{$key} = "$nosave"; +$key = q/chapbackups/; +$ref_files{$key} = "$dir".q|node96.html|; +$noresave{$key} = "$nosave"; +$key = q/chapwalkabout/; +$ref_files{$key} = "$dir".q|node20.html|; +$noresave{$key} = "$nosave"; +$key = q/secbootcloseup/; +$ref_files{$key} = "$dir".q|node68.html|; +$noresave{$key} = "$nosave"; +$key = q/subsecmanualadduser/; +$ref_files{$key} = "$dir".q|node92.html|; +$noresave{$key} = "$nosave"; +$key = q/fighdmountall/; +$ref_files{$key} = "$dir".q|node46.html|; +$noresave{$key} = "$nosave"; +$key = q/fighdschematic/; +$ref_files{$key} = "$dir".q|node30.html|; +$noresave{$key} = "$nosave"; +$key = q/cite_fsstnd-1.2/; +$ref_files{$key} = "$dir".q|node113.html|; +$noresave{$key} = "$nosave"; +$key = q/chlogins/; +$ref_files{$key} = "$dir".q|node79.html|; +$noresave{$key} = "$nosave"; +$key = q/fighdmountroot/; +$ref_files{$key} = "$dir".q|node46.html|; +$noresave{$key} = "$nosave"; +$key = q/cite_device-list/; +$ref_files{$key} = "$dir".q|node113.html|; +$noresave{$key} = "$nosave"; +$key = q/figterminallogins/; +$ref_files{$key} = "$dir".q|node80.html|; +$noresave{$key} = "$nosave"; +$key = q/figharddisklayout/; +$ref_files{$key} = "$dir".q|node37.html|; +$noresave{$key} = "$nosave"; +$key = q/chinit/; +$ref_files{$key} = "$dir".q|node73.html|; +$noresave{$key} = "$nosave"; +$key = q/secNFS/; +$ref_files{$key} = "$dir".q|node16.html|; +$noresave{$key} = "$nosave"; +$key = q/chapuseradmin/; +$ref_files{$key} = "$dir".q|node86.html|; +$noresave{$key} = "$nosave"; +$key = q/tabefficientbackuplevels/; +$ref_files{$key} = "$dir".q|node103.html|; +$noresave{$key} = "$nosave"; +$key = q/chboothalt/; +$ref_files{$key} = "$dir".q|node66.html|; +$noresave{$key} = "$nosave"; +$key = q/secbuffercache/; +$ref_files{$key} = "$dir".q|node65.html|; +$noresave{$key} = "$nosave"; +$key = q/chapmeasureholes/; +$ref_files{$key} = "$dir".q|node111.html|; +$noresave{$key} = "$nosave"; +$key = q/chaptime/; +$ref_files{$key} = "$dir".q|node106.html|; +$noresave{$key} = "$nosave"; +$key = q/secmkfs/; +$ref_files{$key} = "$dir".q|node45.html|; +$noresave{$key} = "$nosave"; +$key = q/figdumpe2fsoutput/; +$ref_files{$key} = "$dir".q|node51.html|; +$noresave{$key} = "$nosave"; +$key = q/figkerneloverview/; +$ref_files{$key} = "$dir".q|node7.html|; +$noresave{$key} = "$nosave"; +$key = q/tabpartitionids/; +$ref_files{$key} = "$dir".q|node38.html|; +$noresave{$key} = "$nosave"; +$key = q/secfilesystems/; +$ref_files{$key} = "$dir".q|node41.html|; +$noresave{$key} = "$nosave"; +$key = q/chapoverview/; +$ref_files{$key} = "$dir".q|node5.html|; +$noresave{$key} = "$nosave"; +$key = q/figbackuphistorytimeline/; +$ref_files{$key} = "$dir".q|node103.html|; +$noresave{$key} = "$nosave"; +$key = q/tabrunlevels/; +$ref_files{$key} = "$dir".q|node76.html|; +$noresave{$key} = "$nosave"; +$key = q/subsecmount/; +$ref_files{$key} = "$dir".q|node46.html|; +$noresave{$key} = "$nosave"; +$key = q/cite_getting-started/; +$ref_files{$key} = "$dir".q|node113.html|; +$noresave{$key} = "$nosave"; +$key = q/chapmem/; +$ref_files{$key} = "$dir".q|node59.html|; +$noresave{$key} = "$nosave"; +$key = q/cite_ext2-defrag/; +$ref_files{$key} = "$dir".q|node113.html|; +$noresave{$key} = "$nosave"; +$key = q/figfstree/; +$ref_files{$key} = "$dir".q|node21.html|; +$noresave{$key} = "$nosave"; +$key = q/cite_network-admin-guide/; +$ref_files{$key} = "$dir".q|node113.html|; +$noresave{$key} = "$nosave"; + +1; + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/invis_anchor.xbm b/sag-0.6.1-www/Invisible/sag-0.6/invis_anchor.xbm new file mode 100644 index 0000000..cc208a3 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/invis_anchor.xbm @@ -0,0 +1,4 @@ +#define dot_anchor_width 1 +#define dot_anchor_height 1 +static char dot_anchor_bits[] = { + 0xfe}; diff --git a/sag-0.6.1-www/Invisible/sag-0.6/labels.pl b/sag-0.6.1-www/Invisible/sag-0.6/labels.pl new file mode 100644 index 0000000..2321c62 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/labels.pl @@ -0,0 +1,117 @@ +# LaTeX2HTML 96.1-h (September 30, 1996) +# Associate labels original text with physical files. + +$key = q/secswapalloc/; +$external_labels{$key} = "$URL/" . q|node64.html|; +$noresave{$key} = "$nosave"; +$key = q/secsingleusermode/; +$external_labels{$key} = "$URL/" . q|node78.html|; +$noresave{$key} = "$nosave"; +$key = q/cite_bootdisk-howto/; +$external_labels{$key} = "$URL/" . q|node113.html|; +$noresave{$key} = "$nosave"; +$key = q/chapbackups/; +$external_labels{$key} = "$URL/" . q|node96.html|; +$noresave{$key} = "$nosave"; +$key = q/chapwalkabout/; +$external_labels{$key} = "$URL/" . q|node20.html|; +$noresave{$key} = "$nosave"; +$key = q/secbootcloseup/; +$external_labels{$key} = "$URL/" . q|node68.html|; +$noresave{$key} = "$nosave"; +$key = q/subsecmanualadduser/; +$external_labels{$key} = "$URL/" . q|node92.html|; +$noresave{$key} = "$nosave"; +$key = q/fighdmountall/; +$external_labels{$key} = "$URL/" . q|node46.html|; +$noresave{$key} = "$nosave"; +$key = q/fighdschematic/; +$external_labels{$key} = "$URL/" . q|node30.html|; +$noresave{$key} = "$nosave"; +$key = q/cite_fsstnd-1.2/; +$external_labels{$key} = "$URL/" . q|node113.html|; +$noresave{$key} = "$nosave"; +$key = q/chlogins/; +$external_labels{$key} = "$URL/" . q|node79.html|; +$noresave{$key} = "$nosave"; +$key = q/fighdmountroot/; +$external_labels{$key} = "$URL/" . q|node46.html|; +$noresave{$key} = "$nosave"; +$key = q/cite_device-list/; +$external_labels{$key} = "$URL/" . q|node113.html|; +$noresave{$key} = "$nosave"; +$key = q/figterminallogins/; +$external_labels{$key} = "$URL/" . q|node80.html|; +$noresave{$key} = "$nosave"; +$key = q/figharddisklayout/; +$external_labels{$key} = "$URL/" . q|node37.html|; +$noresave{$key} = "$nosave"; +$key = q/chinit/; +$external_labels{$key} = "$URL/" . q|node73.html|; +$noresave{$key} = "$nosave"; +$key = q/secNFS/; +$external_labels{$key} = "$URL/" . q|node16.html|; +$noresave{$key} = "$nosave"; +$key = q/chapuseradmin/; +$external_labels{$key} = "$URL/" . q|node86.html|; +$noresave{$key} = "$nosave"; +$key = q/tabefficientbackuplevels/; +$external_labels{$key} = "$URL/" . q|node103.html|; +$noresave{$key} = "$nosave"; +$key = q/chboothalt/; +$external_labels{$key} = "$URL/" . q|node66.html|; +$noresave{$key} = "$nosave"; +$key = q/secbuffercache/; +$external_labels{$key} = "$URL/" . q|node65.html|; +$noresave{$key} = "$nosave"; +$key = q/chapmeasureholes/; +$external_labels{$key} = "$URL/" . q|node111.html|; +$noresave{$key} = "$nosave"; +$key = q/chaptime/; +$external_labels{$key} = "$URL/" . q|node106.html|; +$noresave{$key} = "$nosave"; +$key = q/secmkfs/; +$external_labels{$key} = "$URL/" . q|node45.html|; +$noresave{$key} = "$nosave"; +$key = q/figdumpe2fsoutput/; +$external_labels{$key} = "$URL/" . q|node51.html|; +$noresave{$key} = "$nosave"; +$key = q/figkerneloverview/; +$external_labels{$key} = "$URL/" . q|node7.html|; +$noresave{$key} = "$nosave"; +$key = q/tabpartitionids/; +$external_labels{$key} = "$URL/" . q|node38.html|; +$noresave{$key} = "$nosave"; +$key = q/secfilesystems/; +$external_labels{$key} = "$URL/" . q|node41.html|; +$noresave{$key} = "$nosave"; +$key = q/chapoverview/; +$external_labels{$key} = "$URL/" . q|node5.html|; +$noresave{$key} = "$nosave"; +$key = q/figbackuphistorytimeline/; +$external_labels{$key} = "$URL/" . q|node103.html|; +$noresave{$key} = "$nosave"; +$key = q/tabrunlevels/; +$external_labels{$key} = "$URL/" . q|node76.html|; +$noresave{$key} = "$nosave"; +$key = q/subsecmount/; +$external_labels{$key} = "$URL/" . q|node46.html|; +$noresave{$key} = "$nosave"; +$key = q/cite_getting-started/; +$external_labels{$key} = "$URL/" . q|node113.html|; +$noresave{$key} = "$nosave"; +$key = q/chapmem/; +$external_labels{$key} = "$URL/" . q|node59.html|; +$noresave{$key} = "$nosave"; +$key = q/cite_ext2-defrag/; +$external_labels{$key} = "$URL/" . q|node113.html|; +$noresave{$key} = "$nosave"; +$key = q/figfstree/; +$external_labels{$key} = "$URL/" . q|node21.html|; +$noresave{$key} = "$nosave"; +$key = q/cite_network-admin-guide/; +$external_labels{$key} = "$URL/" . q|node113.html|; +$noresave{$key} = "$nosave"; + +1; + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/linux-logo.gif b/sag-0.6.1-www/Invisible/sag-0.6/linux-logo.gif new file mode 100644 index 0000000..5161948 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/linux-logo.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/long-contents.html b/sag-0.6.1-www/Invisible/sag-0.6/long-contents.html new file mode 100644 index 0000000..879a95f --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/long-contents.html @@ -0,0 +1,174 @@ + + + + +Contents + + + + + + + + next up previous index
+ Next: Introduction +Up: Linux System Administrators' Guide + Previous: Linux System Administrators' Guide +

+

Contents

+ +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/missfont.log b/sag-0.6.1-www/Invisible/sag-0.6/missfont.log new file mode 100644 index 0000000..8b4f02e --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/missfont.log @@ -0,0 +1 @@ +MakeTeXPK cmr10 600 600 1+0/600 ljfour diff --git a/sag-0.6.1-www/Invisible/sag-0.6/next_group_motif.gif b/sag-0.6.1-www/Invisible/sag-0.6/next_group_motif.gif new file mode 100644 index 0000000..833af4d Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/next_group_motif.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/next_group_motif_gr.gif b/sag-0.6.1-www/Invisible/sag-0.6/next_group_motif_gr.gif new file mode 100644 index 0000000..c04fec3 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/next_group_motif_gr.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/next_motif.gif b/sag-0.6.1-www/Invisible/sag-0.6/next_motif.gif new file mode 100644 index 0000000..7a2dbe9 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/next_motif.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/next_motif_gr.gif b/sag-0.6.1-www/Invisible/sag-0.6/next_motif_gr.gif new file mode 100644 index 0000000..1416b1c Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/next_motif_gr.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node1.html b/sag-0.6.1-www/Invisible/sag-0.6/node1.html new file mode 100644 index 0000000..a762486 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node1.html @@ -0,0 +1,22 @@ +Short Contents +

To detailed contents

+

Short Contents

+ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node10.html b/sag-0.6.1-www/Invisible/sag-0.6/node10.html new file mode 100644 index 0000000..a17b90a --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node10.html @@ -0,0 +1,43 @@ + + + + +Logins from terminals + + + + + + + + next up previous contents index
+ Next: Syslog +Up: Major services in a + Previous: init +

+

Logins from terminals

+

+ Logins from terminals (via serial lines) and the console (when not + running X) are provided by the getty  program. init  + starts a separate instance of getty  for each terminal for + which logins are to be allowed. getty  reads the username + and runs the login  program, which reads the password. If + the username and password are correct, + login  runs the shell. When + the shell terminates, i.e., the user logs out, or when login  + terminated because the username and password didn't match, + init  notices this and starts a new instance of getty . + The kernel has no notion of logins, this is all handled by the + system programs. +  +  +  +  +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node100.html b/sag-0.6.1-www/Invisible/sag-0.6/node100.html new file mode 100644 index 0000000..d8d2c7b --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node100.html @@ -0,0 +1,67 @@ + + + + +Simple backups + + + + + + + + next up previous contents index
+ Next: Making backups with tar +Up: Backups + Previous: Selecting the backup tool +

+

Simple backups

+

+ A simple backup scheme is to back up everything once, then back + up everything that has been modified since the previous backup. + The first backup is called a full backup, the subsequent + ones are incremental backups. A full backup is often + more laborius than incremental ones, since there is more data + to write to the tape and a full backup might not fit onto one + tape (or floppy). Restoring from incremental backups can be + many times more work than from a full one. Restoration + can be optimized so that you always back up everything since the + previous full backup; this way, backups are a bit more work, + but there should never be a need to restore more than a full + backup and an incremental backup. +

+ If you want to make backups every day and have six tapes, you could + use tape 1 for the first full backup (say, on a Friday), and + tapes 2 to 5 for the incremental backups (Monday through Thursday). + Then you make a new full backup on tape 6 (second Friday), + and start doing incremental ones with + tapes 2-5 again. You don't want to overwrite tape 1 with + until you've got a new full backup, lest something happens + while you're making the full backup. After you've made a + full backup to tape 6, you want to keep tape 1 somewhere + else, so that when your other backup tapes are destroyed in + the fire, you still have at least something left. When you + need to make the next full backup, you fetch tape 1 and leave + tape 6 in its place. +

+ If you have more than six tapes, you can use the extra ones for + full backups. Each time you make a full backup, you use the oldest + tape. This way you can have full backups from several previous + weeks, which is good if you want to find an old, now deleted file, + or an old version of a file. +

+

+ +
next up previous contents index
+ Next: Making backups with tar +Up: Backups + Previous: Selecting the backup tool +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node101.html b/sag-0.6.1-www/Invisible/sag-0.6/node101.html new file mode 100644 index 0000000..0f72190 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node101.html @@ -0,0 +1,93 @@ + + + + +Making backups with tar + + + + + + + + next up previous contents index
+ Next: Restoring files with tar +Up: Simple backups + Previous: Simple backups +

+ 

Making backups with tar

+

+ A full backup can easily be made with tar : +

+# tar -create -file /dev/ftape /usr/src
+tar: Removing leading / from absolute path names in the archive
+# +
+ The example above uses the GNU version of tar  and its long option + names. The traditional version of tar  only understands single + character options. The GNU version can also handle + backups that don't fit on one tape or floppy, and also very long + paths; not all traditional versions can do these things. (Linux + only uses GNU tar .) +

+ If your backup doesn't fit on one tape, you need to use the + -multi-volume (-M) option: +

+# tar -cMf /dev/fd0H1440 /usr/src
+tar: Removing leading / from absolute path names in the archive
+Prepare volume #2 for /dev/fd0H1440 and hit return:
+# +
+ Note that you should format the floppies before you begin the backup, + or else use another window or virtual terminal and do it when tar  + asks for a new floppy. +

+ After you've made a backup, you should check that it is OK, using + the -compare (-d) option: +

+# tar -compare -verbose -f /dev/ftape
+usr/src/
+usr/src/linux
+usr/src/linux-1.2.10-includes/
+....
+# +
+ Failing to check a backup means that you will not notice that your + backups aren't working until after you've lost the original data. +

+ An incremental backup can be done with tar  using the + -newer (-N) option: +

+# tar -create -newer '8 Sep 1995' -file /dev/ftape /usr/src -verbose
+tar: Removing leading / from absolute path names in the archive
+usr/src/
+usr/src/linux-1.2.10-includes/
+usr/src/linux-1.2.10-includes/include/
+usr/src/linux-1.2.10-includes/include/linux/
+usr/src/linux-1.2.10-includes/include/linux/modules/
+usr/src/linux-1.2.10-includes/include/asm-generic/
+usr/src/linux-1.2.10-includes/include/asm-i386/
+usr/src/linux-1.2.10-includes/include/asm-mips/
+usr/src/linux-1.2.10-includes/include/asm-alpha/
+usr/src/linux-1.2.10-includes/include/asm-m68k/
+usr/src/linux-1.2.10-includes/include/asm-sparc/
+usr/src/patch-1.2.11.gz
+# +
+ Unfortunately, tar  can't notice when a file's inode information + has changed, for example, that it's permission bits have been + changed, or when its name has been changed. This can be worked + around using find  and comparing current filesystem state with + lists of files that have been previously backed up. Scripts and + programs for doing this can be found on Linux ftp sites. +

+

next up previous contents index
+ Next: Restoring files with tar +Up: Simple backups + Previous: Simple backups +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node102.html b/sag-0.6.1-www/Invisible/sag-0.6/node102.html new file mode 100644 index 0000000..a811e6c --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node102.html @@ -0,0 +1,72 @@ + + + + +Restoring files with tar + + + + + + + + next up previous contents index
+ Next: Multilevel backups +Up: Simple backups + Previous: Making backups with tar +

+ 

Restoring files with tar

+

+ The -extract (-x) option for tar  extracts files: +

+# tar -extract -same-permissions -verbose -file /dev/fd0H1440
+usr/src/
+usr/src/linux
+usr/src/linux-1.2.10-includes/
+usr/src/linux-1.2.10-includes/include/
+usr/src/linux-1.2.10-includes/include/linux/
+usr/src/linux-1.2.10-includes/include/linux/hdreg.h
+usr/src/linux-1.2.10-includes/include/linux/kernel.h
+...
+# +
+ You also extract only specific files or directories (which includes + all their files and subdirectories) by naming on the command line: +
+# tar xpvf /dev/fd0H1440 usr/src/linux-1.2.10-includes/include/linux/hdreg.h
+usr/src/linux-1.2.10-includes/include/linux/hdreg.h
+# +
+ Use the -list (-t) option, if you just want to see + what files are on a backup volume: +
+# tar -list -file /dev/fd0H1440
+usr/src/
+usr/src/linux
+usr/src/linux-1.2.10-includes/
+usr/src/linux-1.2.10-includes/include/
+usr/src/linux-1.2.10-includes/include/linux/
+usr/src/linux-1.2.10-includes/include/linux/hdreg.h
+usr/src/linux-1.2.10-includes/include/linux/kernel.h
+...
+# +
+ Note that tar  always reads the backup volume sequentially, + so for large volumes it is rather slow. It is not possible, + however, to use random access database techniques when using + a tape drive or some other sequential medium. +

+ tar  doesn't handle deleted files properly. If you need + to restore a filesystem from a full and an incremental backup, + and you have deleted a file between the two backups, it will + exist again after you have done the restore. This can be a + big problem, if the file has sensitive data that should no + longer be available. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node103.html b/sag-0.6.1-www/Invisible/sag-0.6/node103.html new file mode 100644 index 0000000..ffd932b --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node103.html @@ -0,0 +1,101 @@ + + + + +Multilevel backups + + + + + + + + next up previous contents index
+ Next: What to back up +Up: Backups + Previous: Restoring files with tar +

+

Multilevel backups

+

+ The simple backup method outlined in the previous section + is often quite adequate for personal use or small sites. + For more heavy duty use, multilevel backups are more + appropriate. +

+ The simple method has two backup levels: full and incremental + backups. This can be generalized to any number of levels. + A full backup would be level 0, and the different levels of + incremental backups levels 1, 2, 3, ...At each incremental + backup level you back up everything that has changed since + the previous backup at the same or a previous level. +

+ The purpose for doing this is that it allows a longer + backup history cheaply. In the example in the previous + section, the backup history went back to the previous full backup. + This could be extended by having more tapes, but only a week + per new tape, which might be too expensive. A longer backup + history is useful, since deleted or corrupted files are often + not noticed for a long time. Even a version of a file that is + not very up to date is better than no file at all. +

+ With multiple levels the backup history can be extended + more cheaply. For example, if we buy ten tapes, we could use + tapes 1 and 2 for monthly backups (first Friday each month), + tapes 3 to 6 for weekly backups (other Fridays; note that + there can be five Fridays in one month, so we need four more + tapes), and tapes 7 to 10 for daily backups (Monday to Thursday). + With only four more tapes, we've been able to extend the backup + history from two weeks (after all daily tapes have been + used) to two months. It is true that we can't restore every + version of each file during those two months, but what we can + restore is often good enough. +

+ Figure 10.1 shows which backup level + is used each day, and which backups can be restored from + at the end of the month. +

+

  figure2979
+Figure 10.1: A sample multilevel backup schedule.
+

+

+ Backup levels can also be used to keep filesystem restoration + time to a minimum. If you have many incremental backups with + monotonously growing level numbers, you need to restore all + of them if you need to rebuild the whole filesystem. Instead + you can use level numbers that aren't monotonous, and keep down the + number of backups to restore. +

+ To minimize the number of tapes needed to restore, you could + use a smaller level for each incremental tape. However, then + the time to make the backups increases (each backup copies + everything since the previous full backup). A better scheme + is suggested by the dump  manual page and described by the + table 10.2. Use the following + succession of backup levels: 3, 2, 5, 4, 7, 6, 9, 8, 9...This + keeps both the backup and restore times low. The most you + have to backup is two day's worth of work. The number of tapes + for a restore depends on how long you keep between full backups, + but it is less than in the simple schemes. +

+

  figure2988
+Figure 10.2: Efficient backup scheme using many backup levels
+

+

+ A fancy scheme can reduce the amount of labor needed, but it + does mean there are more things to keep track of. You must + decide if it is worth it. +

+ dump  has built-in support for backup levels. For + tar  and cpio  it must be implemented with shell + scripts. +

+

next up previous contents index
+ Next: What to back up +Up: Backups + Previous: Restoring files with tar +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node104.html b/sag-0.6.1-www/Invisible/sag-0.6/node104.html new file mode 100644 index 0000000..8191564 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node104.html @@ -0,0 +1,45 @@ + + + + +What to back up + + + + + + + + next up previous contents index
+ Next: Compressed backups +Up: Backups + Previous: Multilevel backups +

+

What to back up

+

+ You want to back up as much as possible. The major exception + is software that can be easily reinstalled,gif but even they may have configuration + files that it is important to back up, lest you need to do + all the work to configure them all over again. Another major + exception is the /proc  filesystem; since that only + contains data that the kernel always generates automatically, + it is never a good idea to back it up. Expecially + the /proc/kcore  file is unnecessary, since it is just + an image of your current physical memory; it's pretty large + as well. +

+ Gray areas include the news spool, log files, and many other + things in /var . You must decide what you consider + important. +

+ The obvious things to back up are user files (/home ) and + system configuration files (/etc , but possibly other things + scattered all over the filesystem). +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node105.html b/sag-0.6.1-www/Invisible/sag-0.6/node105.html new file mode 100644 index 0000000..89f5c84 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node105.html @@ -0,0 +1,57 @@ + + + + +Compressed backups + + + + + + + + next up previous contents index
+ Next: Keeping Time +Up: Backups + Previous: What to back up +

+

Compressed backups

+

+ Backups take a lot of space, which can cost quite a lot of money. + To reduce the space needed, the backups can be compressed. There + are several ways of doing this. Some programs have support for + for compression built in; for example, the -gzip (-z) + option for GNU tar  pipes the whole backup through the + gzip  compression program, before writing it to the backup + medium. +

+ Unfortunately, compressed backups can cause trouble. Due to the + nature of how compression works, if a single bit is + wrong, all the rest of the compressed data will be unusable. Some + backup programs have some built in error correction, but no method + can handle a large number of errors. This means that if the + backup is compressed the way GNU tar  does it, with the + whole output compressed as a unit, a single error makes all the + rest of the backup lost. Backups must be reliable, and this + method of compression is not a good idea. +

+ An alternative way is to compress each file separately. This still + means that the one file is lost, but all other files are unharmed. + The lost file would have been corrupted anyway, so this situation + is not much worse than not using compression at all. The afio  + program (a variant of cpio ) can do this. +

+ Compression takes some time, which may make the backup program + unable to write data fast enough for a tape drive.gif This can be + avoided by buffering the output (either internally, if the backup + program if smart enough, or by using another program), but even that + might not work well enough. This should only be a problem on slow + computers. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node106.html b/sag-0.6.1-www/Invisible/sag-0.6/node106.html new file mode 100644 index 0000000..090d2cc --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node106.html @@ -0,0 +1,45 @@ + + + + +Keeping Time + + + + + + + + next up previous contents index
+ Next: Time zones +Up: Linux System Administrators' Guide + Previous: Compressed backups +

+

Keeping Time

+   +

+

+ + Time is an illusion. Lunchtime double so.
+ (Douglas Adams.)
+

+

+ This chapter explains how a Linux system keeps time, + and what you need to do to avoid causing trouble. + Usually, you don't need to do anything about time, but + it is good to understand it. +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node107.html b/sag-0.6.1-www/Invisible/sag-0.6/node107.html new file mode 100644 index 0000000..22006ec --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node107.html @@ -0,0 +1,87 @@ + + + + +Time zones + + + + + + + + next up previous contents index
+ Next: The hardware and software +Up: Keeping Time + Previous: Keeping Time +

+

Time zones

+

+ Time measurement is based on mostly regular natural + phenomena, such as alternating light and dark periods + caused by the rotation of the planet. The total time + taken by two successive periods is constant, but the + lengths of the light and dark period vary. One simple + constant is noon. +

+ Noon is the time of the day when the Sun is at its highest + position. Since the Earth is round,gif noon happens at different times in + different places. This leads to the concept of local + time. Humans measure time in many units, most of which are + tied to natural phenomena like noon. As long as you stay in + the same place, it doesn't matter that local times differ. +

+ As soon as you need to communicate with distant places, you'll + notice the need for a common time. In modern times, most of + the places in the world communicate with most other places in + the world, so a global standard for measuring time has been defined. + This time is called universal time (UT or UTC, formerly + known as Greenwich Mean Time or GMT, since it used to be local + time in Greenwich, England). When people with different local + times need to communicate, they can express times in universal + time, so that there is no confusion about when things should happen. +

+ Each local time is called a time zone. While geography would + allow all places that have noon at the same time + have the same time zone, + politics makes it difficult. For various reasons, many countries + use daylight savings time, that is, they move their + clocks to have more natural light while they work, and then move + the clocks back during winter. Other + countries do not do this. Those that do, do not agree + when the clocks should be moved, and they change the rules + from year to year. This makes time zone conversions definitely + non-trivial. +

+ Time zones are best named by the location or by telling the + difference between local and universal time. In the US and + some other countries, the + local time zones have a name and a three letter abbreviation. + The abbreviations are not unique, however, and should not be + used unless the country is also named. It is better to talk + about the local time in, say, Helsinki, than about East + European time, since not all countries in Eastern Europe follow + the same rules. +

+ Linux has a time zone package that knows about all + existing time zones, and that can easily be updated when the + rules change. All the system administrator needs to do is to + select the appropriate time zone. Also, each user can set + his own time zone--this is important since many people work + with computers in different countries over the Internet. + When the rules for daylight savings time change in your local + time zone, make sure you'll upgrade at least that part of your + Linux system. Other than setting the system time zone and + upgrading the time zone data files, there is little need to + bother about time. +

+

next up previous contents index
+ Next: The hardware and software +Up: Keeping Time + Previous: Keeping Time +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node108.html b/sag-0.6.1-www/Invisible/sag-0.6/node108.html new file mode 100644 index 0000000..262a902 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node108.html @@ -0,0 +1,56 @@ + + + + +The hardware and software clocks + + + + + + + + next up previous contents index
+ Next: Showing and setting time +Up: Keeping Time + Previous: Time zones +

+

The hardware and software clocks

+

+ A personal computer has a battery driven hardware clock. The + battery ensures that the clock will work even if the rest of + the computer is without electricity. The hardware clock can + be set from the BIOS setup screen or from whatever operating + system is running. +

+ The Linux kernel keeps track of time independently from the + hardware clock. During the + boot, Linux sets its own clock to the same time as the hardware + clock. After this, both clocks run independently. Linux + maintains its own clock because looking at the hardware is + slow and complicated. +

+ The kernel clock always shows universal time. This way, the + kernel does not need to know about time zones at all--the simplicity + results in higher reliability and makes it easier to update the + time zone information. Each process handles time zone conversions + itself (using standard tools that are part of the time zone + package). +

+ The hardware clock can be in local time or in universal time. + It is usually better to have it in universal time, because + then you don't need to change the hardware clock when daylight + savings time begins or ends (UTC does not have DST). Unfortunately, + some PC operating systems--including MS-DOS, Windows, OS/2--assume + the hardware clock shows local time. Linux can handle either, but + if the hardware clock shows local time, then it must be modified + when daylight savings time begins or ends (otherwise it wouldn't + show local time). +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node109.html b/sag-0.6.1-www/Invisible/sag-0.6/node109.html new file mode 100644 index 0000000..b7b2d30 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node109.html @@ -0,0 +1,94 @@ + + + + +Showing and setting time + + + + + + + + next up previous contents index
+ Next: When the clock is +Up: Keeping Time + Previous: The hardware and software +

+

Showing and setting time

+

+ In the Debian system, the system time zone is determined by the + symbolic link /etc/localtime . This link points at a time + zone data file that describes the local time zone. The time + zone data files are stored in /usr/lib/zoneinfo . + Other Linux distributions may do this differently. +

+ A user can change his private time zone by setting the + TZ environment variable. If it is unset, the system time zone + is assumed. The syntax of the TZ variable is described in + the tzset (3) manual page. +

+ The date  command shows the current date and + time.gif For example: +

+$ date
+Sun Jul 14 21:53:41 EET DST 1996
+$ +
+ That time is Sunday, 14th of July, 1996, at about ten before + ten at the evening, in the time zone called ``EET DST'' + (which might be East European Daylight Savings Time). + date  can also show the univeral time: +
+$ date -u
+Sun Jul 14 18:53:42 UTC 1996
+$ +
+ date  is also used to set the kernel's software clock: +
+# date 07142157
+Sun Jul 14 21:57:00 EET DST 1996
+# date
+Sun Jul 14 21:57:02 EET DST 1996
+# +
+ See the date  manual page for more details--the syntax + is a bit arcane. Only root can set the time. While + each user can have his own time zone, the clock is the same for + everyone. +

+ date  only shows or sets the software clock. + The clock  commands syncronizes the hardware and + software clocks. + It is used when the system boots, to read the hardware clock + and set the software clock. If you need to set both clocks, you + first set the software clock with date , and then the + hardware clock with clock -w. +

+ The -u option to clock  tells it that the + hardware clock is in universal time. + You must use the -u option correctly. If you + don't, your computer will be quite confused about what the + time is. +

+ The clocks should be changed with care. Many parts of + a Unix system require the clocks to work correctly. For example, + the cron  daemon runs commands periodically. If you change + the clock, it can be confused of whether it needs to run the + commands or not. On one early Unix system, someone set the + clock twenty years into the future, and cron  wanted to + run all the periodic commands for twenty years all at once. + Current versions of cron  can handle this correctly, but + you should still be careful. Big jumps or backward jumps are + more dangeours than smaller or forward ones. +

+

next up previous contents index
+ Next: When the clock is +Up: Keeping Time + Previous: The hardware and software +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node11.html b/sag-0.6.1-www/Invisible/sag-0.6/node11.html new file mode 100644 index 0000000..f4d2848 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node11.html @@ -0,0 +1,39 @@ + + + + +Syslog + + + + + + + + next up previous contents index
+ Next: Periodic command execution: cron +Up: Major services in a + Previous: Logins from terminals +

+

Syslog

+

+ The kernel and many system programs produce error, warning, and + other messages. It is often important that these messages can + be viewed later, even much later, so they should be written to + a file. The program doing this is syslog . It can be + configured to sort the messages to different files according to + writer or degree of importance. For example, kernel messages + are often directed to a separate file from the others, since + kernel messages are often more important and need to be read + regularly to spot problems. +  +  +  +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node110.html b/sag-0.6.1-www/Invisible/sag-0.6/node110.html new file mode 100644 index 0000000..bf24203 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node110.html @@ -0,0 +1,59 @@ + + + + +When the clock is wrong + + + + + + + + next up previous contents index
+ Next: Measuring Holes +Up: Keeping Time + Previous: Showing and setting time +

+

When the clock is wrong

+

+ The Linux software clock is not always accurate. It is kept + running by a periodic timer interrupt generated by + PC hardware. If the + system has too many processes running, it may take too long to + service the timer interrupt, and the software clock starts + slipping behind. + The hardware clock runs independently and is usually more + accurate. If you boot your computer + often (as is the case for most systems that aren't servers), + it will usually keep fairly accurate time. +

+ If you need to adjust the hardware clock, it is usually simplest + to reboot, go into the BIOS setup screen, and do it from there. + This avoids all trouble that changing system time might + cause. + If doing it via BIOS is not an option, set + the new time with date  and clock  (in that order), + but be prepared to reboot, if some part of the system starts + acting funny. +

+ A networked computer (even if just over the modem) can check + its own clock automatically, by comparing it to some other + computer's time. If the other computer is known to keep + very accurate time, then both computers will keep accurate time. + This can be done by using the rdate  + and netdate  commands. + Both check the time of a remote computer (netdate  can + handle several remote computers), and set the local computer's + time to that. By running one these commands regularly, your + computer will keep as accurate time as the remote computer. +

+ META: say something intelligent about NTP +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node111.html b/sag-0.6.1-www/Invisible/sag-0.6/node111.html new file mode 100644 index 0000000..d40ca5a --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node111.html @@ -0,0 +1,61 @@ + + + + +Measuring Holes + + + + + + + + next up previous contents index
+ Next: Glossary (DRAFT) +Up: Linux System Administrators' Guide + Previous: When the clock is +

+

Measuring Holes

+   +

+This appendix contains the interesting part of the program used to measure +the potential for holes in a filesystem. The source distribution of +the book contains the full source code +(sag/measure-holes/measure-holes.c). +

+

+
int process(FILE *f, char *filename) {
+        static char *buf = NULL;
+        static long prev_block_size = -1;
+        long zeroes;
+        char *p;
+
+        if (buf == NULL || prev_block_size != block_size) {
+                free(buf);
+                buf = xmalloc(block_size + 1);
+                buf[block_size] = 1;
+                prev_block_size = block_size;
+        }
+        zeroes = 0;
+        while (fread(buf, block_size, 1, f) == 1) {
+                for (p = buf; *p == '\0'; )
+                        ++p;
+                if (p == buf+block_size)
+                        zeroes += block_size;
+        }
+        if (zeroes > 0)
+                printf("%ld %s\n", zeroes, filename);
+        if (ferror(f)) {
+                errormsg(0, -1, "read failed for `%s'", filename);
+                return -1;
+        }
+        return 0;
+}
+ +

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node112.html b/sag-0.6.1-www/Invisible/sag-0.6/node112.html new file mode 100644 index 0000000..f9ef889 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node112.html @@ -0,0 +1,107 @@ + + + + +Glossary (DRAFT) + + + + + + + + next up previous contents index
+ Next: References +Up: Linux System Administrators' Guide + Previous: Measuring Holes +

+

Glossary (DRAFT)

+

+

+ +The Librarian of the Unseen University
+had unilaterally decided to aid comprehension
+by producing an Orang-utan/Human Dictionary.
+He'd been working on it for three months. +

+It wasn't easy. He'd got as far as `Oook.' +

+(Terry Pratchett, ``Men At Arms'')
+

+

+This is a short list of word definitions for concepts relating to +Linux and system administration. The page references are to the +first or most important place where the word is used. +

+

ambition +
+ The act of writing funny sentences in the hope of getting them + into the Linux cookie file. +

+

application program +
(p. gif) + Software that does something useful. The results of using an + application program is what the computer was bought for. + See also system program, operating system. +

+

daemon +
A process lurking in the background, usually unnoticed, until + something triggers it into action. For example, the update  + daemon wakes up every thirty seconds or so to flush the buffer + cache, and the sendmail  daemon awakes whenever someone sends + mail. +

+

file system +
(p. gif) + The methods and data structures that an operating + system uses to keep track of files on a disk or partition; + the way the files are organized on the disk. Also used about + a partition or disk that is used to store the files + or the type of the filesystem. +

+

glossary +
+ A list of words and explanations of what they do. Not + to be confused with a dictionary, which is also a list of + words and explanations. +

+

kernel +
(p. gif) + Part of an operating system that implements the interaction with + hardware and the sharing of resources. See also system program. +

+

operating system +
(p. gif) + Software that shares a computer system's resources (processor, + memory, disk space, network bandwidth, and so on) between + users and the application programs they run. Controls access + to the system to provide security. See also kernel, system program, + application program. +

+

system call +
(p. gif) + The services provided by the kernel to application programs, + and the way in which they are invoked. See section 2 of the + manual pages. +

+

system program +
(p. gif) + Programs that implement high level functionality of an operating + system, i.e., things that aren't directly dependent on the + hardware. May sometimes require special privileges to run + (e.g., for delivering electronic mail), but often just commonly + thought of as part of the system (e.g., a compiler). See also + application program, kernel, operating system. +

+

+

+

next up previous contents index
+ Next: References +Up: Linux System Administrators' Guide + Previous: Measuring Holes +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node113.html b/sag-0.6.1-www/Invisible/sag-0.6/node113.html new file mode 100644 index 0000000..cbbcd3c --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node113.html @@ -0,0 +1,62 @@ + + + + +References + + + + + + + + next up previous contents index
+ Next: Index +Up: Linux System Administrators' Guide + Previous: Glossary (DRAFT) +

+

References

+

+
Anv
+Peter Anvin. +Linux device list. +A list of major and minor device numbers for Linux devices. Now + included in the kernel sources. +

+

Cha
+Graham Chapman. +Bootdisk howto. +Available with other Linux HOWTO's. +

+

Kir
+Olaf Kirch. +Linux network administrators' guide. +

+

Qui95
+Daniel Quinlan. +Linux Filesystem Structure--Release 1.2, March 1995. +A description of and a proposal for a standard Linux directory tree, + with the intention is to make it easier to package software and administer + Linux systems by making files appear in standard places. Follows fairly + closely traditional Unix practice, and has got support from most Linux + distributions. Available via FTP from ftp.funet.fi, directory + /pub/Linux/doc/fsstnd. +

+

TV
+Stephen Tweedie and Alexei Vovenko. +Linux filesystem defragmenter. +Available electronically from \ + ftp://sunsite.unc.edu/pub/Linux/system/Filesystems/defrag-0.6.tar.gz. +

+

Wel
+Matt Welsh. +Installation and getting started guide. +
+

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node114.html b/sag-0.6.1-www/Invisible/sag-0.6/node114.html new file mode 100644 index 0000000..c1ba6a9 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node114.html @@ -0,0 +1,789 @@ + + + + +Index + + + + + + + + next up previous contents
+ Next: About this document +Up: Linux System Administrators' Guide + Previous: References +

+

Index

+
+
.hushlogin +
What login does +
.profile +
Shell startup | Shell startup | Initial environment: /etc/skel +
/bin +
The filesystem layout | The root filesystem | The root filesystem | The /usr filesystem | Partitioning schemes +
/bin/sh +
Mounting and unmounting | init comes first | Shell startup +
/boot +
The root filesystem +
/dev +
The filesystem layout | The root filesystem | The \texttt/dev\index/dev directory | The /dev directory | Two kinds of devices | Partitioning schemes +
/dev/fd0 +
Floppies | Formatting +
/dev/fd0H1440 +
Floppies +
/dev/fd1 +
Floppies +
/dev/hda +
Hard disks +
/dev/hda1 +
Device files and partitions +
/dev/hda2 +
Mounting and unmounting | Mounting and unmounting +
/dev/hdb +
Hard disks +
/dev/hdc +
Hard disks +
/dev/hdd +
Hard disks +
/dev/MAKEDEV +
The /dev directory +
/dev/MAKEDEV.local +
The /dev directory +
/dev/sda +
Two kinds of devices | Hard disks +
/dev/sdb +
Hard disks +
/dev/sdb7 +
Device files and partitions +
/dev/tty +
Configuring init to +
/dev/tty1 +
Configuring init to | Configuring init to +
/etc +
The filesystem layout | The root filesystem | The \texttt/etc\index/etc directory | The /etc directory | The /etc directory | Partitioning schemes | What to back up +
/etc/csh.cshrc +
The /etc directory +
/etc/csh.login +
The /etc directory +
/etc/fastboot +
Checking filesystem integrity with | Checking filesystem integrity with +
/etc/fdprm +
The /etc directory | Floppies +
/etc/fstab +
The /etc directory | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Adding more disk space | Using a swap space | Using a swap space | Using a swap space +
/etc/group +
The /etc directory | Access control | Creating a user by | Changing user properties | Removing a user +
/etc/init.d/rc +
Run levels +
/etc/inittab +
The /etc directory | Configuring \textttinit\indexinit to start | Configuring init to | Configuring init to | Configuring init to | Configuring init to | Configuring init to | Run levels | Run levels | Run levels | Special configuration in \texttt/etc/inittab\index/etc/inittab | Special configuration in /etc/inittab +
/etc/issue +
The /etc directory | Logins via terminals +
/etc/localtime +
Showing and setting time +
/etc/login.defs +
The /etc directory +
/etc/magic +
The /etc directory +
/etc/motd +
The /etc directory | What login does +
/etc/mtab +
The /etc directory +
/etc/nologin +
What login does +
/etc/passwd +
The /etc directory | The /etc directory | The /etc directory | Booting in single user | Access control | \texttt/etc/passwd\index/etc/passwd and other informative | /etc/passwd and other informative | /etc/passwd and other informative | Creating a user by | Changing user properties | Changing user properties | Removing a user +
/etc/printcap +
The /etc directory +
/etc/profile +
The /etc directory | Shell startup | Shell startup | Initial environment: /etc/skel +
/etc/rc +
The /etc directory | The /etc directory +
/etc/rc.d +
The /etc directory +
/etc/rc?.d +
The /etc directory +
/etc/securetty +
The /etc directory | Access control +
/etc/shadow +
The /etc directory | The /etc directory | Access control | /etc/passwd and other informative +
/etc/shadow.group +
Access control +
/etc/shells +
The /etc directory | The /etc directory +
/etc/skel +
Initial environment: \texttt/etc/skel\index/etc/skel | Initial environment: /etc/skel | Initial environment: /etc/skel | Initial environment: /etc/skel | Creating a user by +
/etc/skel/.profile +
Initial environment: /etc/skel +
/etc/termcap +
The /etc directory | The /etc directory | The /etc directory +
/extra-swap +
Creating a swap space +
/home +
The filesystem layout | Background | Background | Background | Background | The root filesystem | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Partitioning schemes | Examples of hard disk | What to back up +
/home/staff +
Background +
/home/students +
Background +
/lib +
The filesystem layout | The root filesystem | Partitioning schemes +
/lib/modules +
The root filesystem +
/mnt +
The root filesystem | The root filesystem | The root filesystem +
/mnt/dosa +
The root filesystem +
/mnt/exta +
The root filesystem +
/proc +
The root filesystem | The \texttt/proc\index/proc filesystem | The /proc filesystem | The /proc filesystem | The /proc filesystem | The /proc filesystem | The /proc filesystem | The /proc filesystem | Filesystems galore | What to back up +
/proc/1 +
The /proc filesystem +
/proc/cpuinfo +
The /proc filesystem +
/proc/devices +
The /proc filesystem +
/proc/dma +
The /proc filesystem +
/proc/filesystems +
The /proc filesystem +
/proc/interrupts +
The /proc filesystem +
/proc/ioports +
The /proc filesystem +
/proc/kcore +
The /proc filesystem | Filesystems galore | What to back up +
/proc/kmsg +
The /proc filesystem +
/proc/ksyms +
The /proc filesystem +
/proc/loadavg +
The /proc filesystem +
/proc/meminfo +
The /proc filesystem | The /proc filesystem | Using a swap space +
/proc/modules +
The /proc filesystem +
/proc/net +
The /proc filesystem +
/proc/self +
The /proc filesystem +
/proc/stat +
The /proc filesystem +
/proc/uptime +
The /proc filesystem +
/proc/version +
The /proc filesystem +
/root +
The root filesystem +
/sbin +
The root filesystem +
/sbin/getty +
Logins from terminals +
/sbin/init +
init | The boot process in | init | init comes first +
/sbin/update +
The buffer cache +
/tmp +
Periodic command execution: cron | The root filesystem | The root filesystem | The /var filesystem | Mounting and unmounting | Mounting and unmounting | Partitioning schemes | init comes first | Special configuration in /etc/inittab +
/usr +
The filesystem layout | Background | Background | Background | Background | Background | Background | Background | Background | The root filesystem | The \texttt/usr\index/usr filesystem | The /usr filesystem | The /usr filesystem | The /usr filesystem | The /usr filesystem | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Partitioning schemes | Partitioning schemes | Partitioning schemes | Partitioning schemes | Examples of hard disk | Booting in single user | Booting in single user +
/usr/adm/messages +
Formatting +
/usr/bin +
The /usr filesystem +
/usr/doc +
The /usr filesystem +
/usr/include +
The /usr filesystem +
/usr/info +
The /usr filesystem +
/usr/lib +
The /usr filesystem | The /usr filesystem | The /usr filesystem +
/usr/lib/libc.a +
Background +
/usr/lib/zoneinfo +
Showing and setting time +
/usr/local +
The /usr filesystem | The /usr filesystem | The /var filesystem +
/usr/local/bin +
The /usr filesystem +
/usr/man +
The /usr filesystem +
/usr/man/cat* +
The /var filesystem +
/usr/man/man* +
The /var filesystem +
/usr/sbin +
The /usr filesystem +
/usr/var +
Background | Background +
/usr/X11R6 +
The /usr filesystem | The /usr filesystem | The /usr filesystem +
/usr/X386 +
The /usr filesystem +
/var +
The filesystem layout | Background | Background | Background | Background | Background | Background | The root filesystem | The \texttt/var\index/var filesystem | The /var filesystem | The /var filesystem | Mounting and unmounting | What to back up +
/var/adm/messages +
Background +
/var/catman +
The /var filesystem | The /var filesystem +
/var/lib +
The /var filesystem +
/var/local +
The /var filesystem +
/var/lock +
The /var filesystem | The /var filesystem | The /var filesystem +
/var/log +
The /var filesystem | The /var filesystem +
/var/log/messages +
The /var filesystem +
/var/log/wtmp +
The /var filesystem | What login does +
/var/man +
The /var filesystem +
/var/run +
The /var filesystem +
/var/run/utmp +
The /var filesystem | What login does +
/var/spool +
The /var filesystem | The /var filesystem +
/var/spool/mail +
Mail | The /var filesystem +
/var/tmp +
Periodic command execution: cron | The root filesystem | The /var filesystem | The /var filesystem | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting +
/vmlinuz +
The root filesystem +
active partition +
The boot process in +
adduser +
Creating a user +
afio +
Compressed backups +
application program +
Various parts of an +
at +
Periodic command execution: \textttcron\indexcron | Periodic command execution: cron | Removing a user +
Athena +
Graphical user interface +
axe +
More about shutdowns +
background processes +
+
and shutting down +
More about shutdowns +
+
backups +
Emergency boot floppies +
badblocks +
Formatting | Formatting | Formatting | Creating a filesystem | Creating a filesystem | Creating a filesystem | Creating a filesystem | Creating a filesystem | Checking for disk errors | Checking for disk errors +
bdflush +
Other tools for all | The buffer cache | The buffer cache | The buffer cache +
BIOS +
The boot process in +
boot process +
init +
boot record +
+
master +
see MBR +
partition +
see partition boot record +
+
boot sector +
An overview of boots +
booting +
An overview of boots +
+
from emergency floppy +
Emergency boot floppies +
from floppy +
The boot process in +
from hard disk +
The boot process in +
messages +
The boot process in +
+
bootstrap loader +
An overview of boots +
BSD +
Important parts of the +
buffer cache +
Important parts of the | An overview of boots | More about shutdowns | More about shutdowns +
C compiler +
Various parts of an +
cache +
More about shutdowns +
centralized computing +
Networking +
cfdisk +
Partitioning a hard disk +
checking a filesystem +
The boot process in +
chfn +
Changing user properties +
chmod +
Creating a user by | Changing user properties +
chown +
Creating a user by +
chsh +
The /etc directory | Changing user properties +
cleaning temporary files +
Periodic command execution: cron +
clock +
Showing and setting time | Showing and setting time | When the clock is +
communication +
Mail +
compression of kernel +
The boot process in +
console +
The boot process in +
cpio +
Selecting the backup tool | Selecting the backup tool | Selecting the backup tool | Selecting the backup tool | Selecting the backup tool | Selecting the backup tool | Multilevel backups | Compressed backups +
crack +
Access control | Access control +
crash +
More about shutdowns +
cron +
Periodic command execution: \textttcron\indexcron | Periodic command execution: cron | Periodic command execution: cron | Periodic command execution: cron | What login does | Removing a user | Showing and setting time | Showing and setting time | Showing and setting time +
crontab +
Periodic command execution: cron +
crying +
Boots And Shutdowns +
ctrl-alt-del +
Rebooting +
curs_termcap +
The /etc directory +
daemons +
+
at +
see at +
cron +
see cron +
init +
see /sbin/init +
rlogin +
see rlogin +
starting +
The boot process in +
telnet +
see telnet +
+
data loss +
An overview of boots +
date +
Showing and setting time | Showing and setting time | Showing and setting time | Showing and setting time | Showing and setting time | Showing and setting time | When the clock is +
dd +
Disks without filesystems | Disks without filesystems +
debugfs +
Checking filesystem integrity with | Other tools for the | Other tools for the +
deluser +
Removing a user +
device driver +
Important parts of the +
device driver configuration +
The boot process in +
df +
The /etc directory | Other tools for all +
disk cache +
More about shutdowns +
distributed computing +
Networking +
documentation +
Various parts of an +
DouBle +
Tips for saving disk +
du +
Other tools for all +
dump +
Mounting and unmounting | Other tools for the | Selecting the backup tool | Selecting the backup tool | Selecting the backup tool | Selecting the backup tool | Multilevel backups | Multilevel backups +
dumpe2fs +
Other tools for the | Other tools for the | Other tools for the +
e-mail +
see electronic mail +
e2fsck +
Checking filesystem integrity with | Checking filesystem integrity with | Checking filesystem integrity with | Checking filesystem integrity with | Checking for disk errors | Other tools for the | Other tools for the | Other tools for the +
electronic mail +
Mail +
elm +
Mail +
emergency floppy +
+
making +
Emergency boot floppies +
using +
Emergency boot floppies +
+
emergency shutdown +
see shutdown, emergency +
error messages +
Syslog +
exec +
Logins via terminals +
fault tolerance +
Networking +
fdformat +
Formatting | Formatting | Formatting | Formatting +
fdisk +
The MBRboot sectors | Partition types | Partition types | Partition types | Partitioning a hard disk | Partitioning a hard disk | Partitioning a hard disk | Partitioning a hard disk +
fdisk -l +
The MBRboot sectors +
file +
The /etc directory | The /etc directory | The /etc directory +
filesystem driver +
Important parts of the +
Filesystem Standard +
see FSSTND +
filesystems +
+
root +
The boot process in +
+
find +
Removing a user | Making backups with tar +
fips +
Partitioning a hard disk +
floppy +
+
booting from +
see booting +
+
floppy drive +
Emergency boot floppies +
floppy-image +
Disks without filesystems +
fork +
Logins via terminals +
free +
The /proc filesystem | Using a swap space | Using a swap space | Allocating swap space +
fsck +
Formatting | Formatting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Checking filesystem integrity with | Checking filesystem integrity with | Checking filesystem integrity with | Checking filesystem integrity with | Checking filesystem integrity with | Checking filesystem integrity with | Checking filesystem integrity with | Checking filesystem integrity with | Checking for disk errors | Other tools for the | The boot process in | Booting in single user | Booting in single user | Booting in single user | Booting in single user | Booting in single user +
FSSTND +
The filesystem layout +
fstab +
Mounting and unmounting +
ftpd +
The /etc directory +
games +
Various parts of an +
GCC +
Various parts of an +
getty +
init | Logins from terminals | Logins from terminals | Logins from terminals | Logins from terminals | Network logins | Network logins | Network logins | The /etc directory | The boot process in | The boot process in | init | init comes first | init comes first | Configuring \textttinit\indexinit to start | Configuring init to | Configuring init to | Configuring init to | Configuring init to | Configuring init to | Configuring init to | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | Logins via the network | Logins via the network +
graphical user interface +
Graphical user interface +
group +
The /etc directory +
gzexe +
Tips for saving disk +
gzip +
Tips for saving disk | Compressed backups +
hard disk +
+
booting from +
see booting +
+
hardware configuration +
The boot process in +
improper shutdown +
see shutdown, emergency +
incoming mailbox +
Mail +
inetd +
Logins via the network +
init +
\textttinit\indexinit | init | init | init | init | init | init | init | Logins from terminals | Logins from terminals | The /etc directory | The /etc directory | An overview of boots | An overview of boots | The boot process in | The boot process in | The boot process in | The boot process in | More about shutdowns | \textttinit\indexinit | init | init | init | see /sbin/init | \textttinit\indexinit comes first | init comes first | init comes first | init comes first | init comes first | init comes first | init comes first | init comes first | init comes first | init comes first | init comes first | init comes first | init comes first | init comes first | init comes first | init comes first | init comes first | init comes first | Configuring \textttinit\indexinit to start | Configuring init to | Configuring init to | Configuring init to | Configuring init to | Configuring init to | Configuring init to | Configuring init to | Configuring init to | Run levels | Run levels | Run levels | Run levels | Run levels | Run levels | Special configuration in /etc/inittab | Special configuration in /etc/inittab | Special configuration in /etc/inittab | Special configuration in /etc/inittab | Booting in single user | Booting in single user | Booting in single user | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals +
+
and ctrl-alt-del +
Rebooting +
single user mode +
Single user mode +
+
inittab +
Configuring init to | Special configuration in /etc/inittab +
installation disks +
Emergency boot floppies +
kernel +
Various parts of an +
kernel compression +
The boot process in +
kernel configuration +
The boot process in +
kernel panic +
The boot process in +
killing processes +
init +
kill -HUP 1 +
Configuring init to +
last +
What login does +
letter +
see electronic mail +
LILO +
The boot process in | The boot process in +
Linux Filesystem Standard +
see FSSTND +
log files +
Syslog +
logging in +
Logins from terminals +
logging out +
Logins from terminals +
login +
Logins from terminals | Logins from terminals | Logins from terminals | The /etc directory | The /var filesystem | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | Logins via terminals | What \textttlogin\indexlogin does | What login does | What login does | What login does | What login does +
lpr +
Two kinds of devices +
ls +
Two kinds of devices | Two kinds of devices | The buffer cache +
ls -l +
Two kinds of devices +
lseek +
What are filesystems? +
magic +
The /etc directory +
mail, electronic +
see electronic mail +
mailbox +
Mail +
MAKEDEV +
The /dev directory +
master boot record +
The boot process in +
MBR +
The boot process in +
memory management +
Important parts of the +
mkdir +
Creating a user by +
mke2fs +
Other tools for the +
mkfs +
Formatting | Formatting | Creating a filesystem | Creating a filesystem | Creating a filesystem | Creating a filesystem +
mkfs) +
Introduction +
mkswap +
Creating a swap space | Creating a swap space | Creating a swap space | Creating a swap space | Creating a swap space +
Motif +
Graphical user interface +
mount +
The /etc directory | The /etc directory | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting | Mounting and unmounting +
mount -a +
Mounting and unmounting +
mounting +
+
root filesystem +
The boot process in +
+
mounting filesystems +
init +
mtools +
Mounting and unmounting +
multitasking +
Important parts of the +
multiuser mode +
init +
netdate +
When the clock is | When the clock is +
nethack +
Special configuration in /etc/inittab | Booting in single user +
Network File System +
see NFS +
network file systems +
Network file systems +
network management +
Important parts of the +
NFS +
Network file systems +
now +
Other tools for all +
Open Look +
Graphical user interface +
operating system +
Various parts of an +
panic +
The boot process in +
partition boot record +
The boot process in +
partition table +
The boot process in +
passwd +
The /etc directory | Access control | /etc/passwd and other informative | Creating a user by | Changing user properties +
periodic command execution +
see cron and at +
pine +
Mail +
printer queue +
Printing +
proc +
The /proc filesystem +
process management +
Important parts of the +
programming languages +
Various parts of an +
ps +
Allocating swap space +
ramdisk +
Emergency boot floppies +
rdate +
When the clock is +
rdev +
Mounting and unmounting | The boot process in | The boot process in +
read-only root filesystem +
The boot process in +
rebooting +
Rebooting +
restore +
Other tools for the +
rlogin +
Network logins | Network logins | Logins via the network +
root +
init | Mounting and unmounting | Mounting and unmounting +
root filesystem +
The boot process in +
run level +
init +
sendmail +
Mail | Glossary (DRAFT) +
serial terminal +
The boot process in +
setfdprm +
The /etc directory | The /etc directory | Floppies | Floppies | Formatting +
sharing printers +
Printing +
shutdown +
More about shutdowns | More about shutdowns | More about shutdowns | More about shutdowns | Rebooting | What login does +
+
actions +
More about shutdowns +
emergency +
More about shutdowns +
triple syncs +
More about shutdowns +
using +
More about shutdowns +
+
shutdown message +
More about shutdowns +
shutting down +
More about shutdowns +
single user mode +
init | Single user mode +
smail +
Mail +
social relations +
Printing +
socket +
Important parts of the +
spooling +
Printing +
starting a computer +
An overview of boots +
startup messages +
The boot process in +
stopping the processor +
init +
su +
Access control | Disabling a user temporarily +
sudo +
Mounting and unmounting +
swap space +
Important parts of the +
swapoff +
Using a swap space +
swapon +
Using a swap space | Using a swap space +
sync +
Other tools for all | The buffer cache | The buffer cache | The buffer cache | The buffer cache | More about shutdowns | More about shutdowns +
syslog +
Syslog | The /var filesystem | The /proc filesystem | Formatting | What login does +
system call +
Various parts of an +
system crash +
More about shutdowns +
system program +
Various parts of an +
sysvinit +
init comes first | init comes first +
tail +
Disabling a user temporarily +
tar +
Disks without filesystems | Disks without filesystems | Selecting the backup tool | Selecting the backup tool | Selecting the backup tool | Selecting the backup tool | Selecting the backup tool | Selecting the backup tool | Making backups with \texttttar\indextar | Making backups with tar | Making backups with tar | Making backups with tar | Making backups with tar | Making backups with tar | Making backups with tar | Making backups with tar | Restoring files with \texttttar\indextar | Restoring files with tar | Restoring files with tar | Restoring files with tar | Multilevel backups | Compressed backups | Compressed backups +
telinit +
Run levels | Booting in single user +
telnet +
Various parts of an | Network logins | Network logins | Logins via the network +
temporary files +
Periodic command execution: cron +
termcap +
The /etc directory +
terminal +
The boot process in +
terminfo +
The /etc directory +
text mode +
The boot process in +
time +
Showing and setting time +
top +
Using a swap space +
tune2fs +
Other tools for the | Other tools for the +
tzset +
Showing and setting time +
umask +
Mounting and unmounting +
umount +
Mounting and unmounting | Mounting and unmounting | Mounting and unmounting +
unmount +
Mounting and unmounting +
unmounting filesystems +
init +
update +
Other tools for all | Other tools for all | Other tools for all | The buffer cache | The buffer cache | More about shutdowns | More about shutdowns | Glossary (DRAFT) +
user authentication +
Logins from terminals +
user mode +
Various parts of an +
useradd +
Creating a user +
userdel +
Removing a user +
utmp +
What login does | What login does | What login does +
video card +
The boot process in +
video mode +
The boot process in +
vigr +
Creating a user by | Changing user properties +
vipw +
Creating a user by | Creating a user by | Changing user properties +
virtual console +
The boot process in +
virtual filesystem +
Important parts of the +
w +
What login does +
warning messages +
Syslog +
who +
What login does +
Windows 95 +
see crying +
wtmp +
What login does | What login does +
X Window System +
init | Graphical user interface +
xterm +
More about shutdowns +
zip +
Tips for saving disk +

+


+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node115.html b/sag-0.6.1-www/Invisible/sag-0.6/node115.html new file mode 100644 index 0000000..3edb344 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node115.html @@ -0,0 +1,27 @@ + + + + + About this document ... + + + + + + + + next up previous contents index
+Up: Linux System Administrators' Guide + Previous: Index +

+

About this document ...

+

+ Linux System Administrators' Guide 0.6

+This document was generated using the LaTeX2HTML translator Version 96.1-h (September 30, 1996) Copyright © 1993, 1994, 1995, 1996, Nikos Drakos, Computer Based Learning Unit, University of Leeds.

The command line arguments were:
+latex2html sag.

The translation was initiated by Lars Wirzenius on Sat Nov 15 02:32:11 EET 1997

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node12.html b/sag-0.6.1-www/Invisible/sag-0.6/node12.html new file mode 100644 index 0000000..df1afab --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node12.html @@ -0,0 +1,47 @@ + + + + +Periodic command execution: cron and at + + + + + + + + next up previous contents index
+ Next: Graphical user interface +Up: Major services in a + Previous: Syslog +

+ 

Periodic command execution: cron  and at

+

+ Both users and system administrators often need to run + commands periodically. For example, the system + administrator might want to run a command to clean the + directories with temporary files (/tmp  and /var/tmp ) + from old files, to keep the disks from filling up, since not + all programs clean up after themselves correctly. +  +  +  +

+ The cron  service is set up to do this. Each user has + a crontab , where he lists the commands he wants to + execute and the times they should be executed. The cron  + daemon takes care of starting the commands when specified. +  +

+ The at  service is similar to cron , but it is + once only: the command is executed at the given time, but it + is not repeated. +  +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node13.html b/sag-0.6.1-www/Invisible/sag-0.6/node13.html new file mode 100644 index 0000000..413ef3f --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node13.html @@ -0,0 +1,48 @@ + + + + +Graphical user interface + + + + + + + + next up previous contents index
+ Next: Networking +Up: Major services in a + Previous: Periodic command execution: cron +

+

Graphical user interface

+

+ UNIX and Linux don't incorporate the user interface into the + kernel; instead, they let it be implemented by user level + programs. This applies for both text mode and graphical + environments. +

+ This arrangement makes the system more flexible, but has + the disadvantage that it is simple to implement a different + user interface for each program, making the system + harder to learn. +

+ The graphical environment primarily used with Linux is called + the X Window System (X for short). X also does not implement + a user interface; it only implements a window system, i.e., tools + with which a graphical user interface can be implemented. + The three most popular user interface styles implemented over + X are Athena, Motif, and Open Look. +  +  +  +  +  +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node14.html b/sag-0.6.1-www/Invisible/sag-0.6/node14.html new file mode 100644 index 0000000..0553103 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node14.html @@ -0,0 +1,45 @@ + + + + +Networking + + + + + + + + next up previous contents index
+ Next: Network logins +Up: Major services in a + Previous: Graphical user interface +

+

Networking

+

+ Networking is the act of connecting two or more computers so that + they can communicate with each other. The actual methods of + connecting and communicating are slightly complicated, + but the end result is very useful. +

+ UNIX operating systems have many networking features. Most basic + services--filesystems, printing, backups, etc--can be done + over the network. This can make system administration easier, + since it allows centralized administration, while still reaping + in the benefits of microcomputing and distributed computing, such + as lower costs and better fault tolerance. +  +  +  +

+ However, this book merely glances at networking; see the + Linux Network Administrators' Guide for more information, + including a basic description of how networks operate. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node15.html b/sag-0.6.1-www/Invisible/sag-0.6/node15.html new file mode 100644 index 0000000..ae4955a --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node15.html @@ -0,0 +1,45 @@ + + + + +Network logins + + + + + + + + next up previous contents index
+ Next: Network file systems +Up: Major services in a + Previous: Networking +

+

Network logins

+

+ Network logins work a little differently than normal logins. + There is a separate physical serial line for each terminal via + which it is possible to log in. For each person logging in via + the network, there is a separate virtual network connection, + and there can be any number of thesegif. It is + therefore not possible to run a separate getty  for each + possible virtual connection. There are also several different + ways to log in via a network, telnet  and rlogin  being + the major ones in TCP/IP networks. +

+ Network logins have, instead of a herd of getty s, a + single daemon per way of logging in (telnet  and rlogin  + have separate daemons) that listens for all incoming login attempts. + When it notices one, it starts a new instance of itself to handle that + single attempt; the original instance continues to listen for + other attempts. The new instance works similarly to getty . +  +  +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node16.html b/sag-0.6.1-www/Invisible/sag-0.6/node16.html new file mode 100644 index 0000000..437afda --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node16.html @@ -0,0 +1,43 @@ + + + + +Network file systems + + + + + + + + next up previous contents index
+ Next: Mail +Up: Major services in a + Previous: Network logins +

+

Network file systems

+

+  +

+ One of the more useful things that can be done with networking + services is sharing files via a network file system. The + one usually used is called the Network File System, or NFS, + developed by Sun. +  +  +  +

+ With a network file system any file operations done by a program + on one machine are sent over the network to another computer. + This fools the program to think that all the files on the other + computer are actually on the computer the program is running on. + This makes information sharing extremely simple, since it requires + no modifications to programs. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node17.html b/sag-0.6.1-www/Invisible/sag-0.6/node17.html new file mode 100644 index 0000000..fb2ffd3 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node17.html @@ -0,0 +1,54 @@ + + + + +Mail + + + + + + + + next up previous contents index
+ Next: Printing +Up: Major services in a + Previous: Network file systems +

+

Mail

+

+ Electronic mail is usually the most important method for + communicating via computer. An electronic letter is stored + in a file using a special format, and special mail programs + are used to send and read the letters. +  +  +  +  +  +

+ Each user has an incoming mailbox (a file in the + special format), where all new mail + is stored. When someone sends mail, the mail program + locates the receiver's mailbox and appends the letter to the + mailbox file. If the receiver's mailbox is in another + machine, the letter is sent to the other machine, which delivers + it to the mailbox as it best sees fit. +  +  +

+ The mail system consists of many programs. The delivery of mail + to local or remote mailboxes is done by one program (the + mail transfer agent or MTA, e.g., + sendmail  or smail ), while the programs users use + are many and varied (mail user agent or MUA, + e.g., pine  or elm ). The + mailboxes are usually stored in /var/spool/mail . +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node18.html b/sag-0.6.1-www/Invisible/sag-0.6/node18.html new file mode 100644 index 0000000..b2678fd --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node18.html @@ -0,0 +1,47 @@ + + + + +Printing + + + + + + + + next up previous contents index
+ Next: The filesystem layout +Up: Major services in a + Previous: Mail +

+

Printing

+

+ Only one person can use a printer at one time, but it is + uneconomical not to share printers between users. The printer + is therefore managed by software that implements a print + queue: all print jobs are put into a queue and whenever the + printer is done with one job, the next one is sent to it + automatically. This relieves the users from organizing the + print queue and fighting over control of the printer.gif +  +  +  +

+ The print queue software also spools the printouts on + disk, i.e., the text is kept in a file while the job is in the + queue. This allows an application program to spit out the + print jobs quickly to the print queue software; the application + does not have to wait until the job is actually printed to + continue. This is really convenient, since it allows one to + print out one version, and not have to wait for it to be printed + before one can make a completely revised new version. +  +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node19.html b/sag-0.6.1-www/Invisible/sag-0.6/node19.html new file mode 100644 index 0000000..1535583 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node19.html @@ -0,0 +1,43 @@ + + + + +The filesystem layout + + + + + + + + next up previous contents index
+ Next: Overview of the Directory +Up: Overview of a Linux + Previous: Printing +

+

The filesystem layout

+

+ The filesystem is divided into many parts; usually along + the lines of a root filesystem with /bin , /lib , + /etc , /dev , and a few others; a /usr  filesystem + with programs and unchanging data; a /var  filesystem with + changing data (such as log files); and a /home  filesystem + for everyone's personal files. Depending on the hardware + configuration and the decisions of the system administrator, + the division can be different; it can even be all in one + filesystem. +

+ Chapter 3 describes the filesystem layout + in some detail; the Linux Filesystem Standard covers it + in somewhat more detail. +  +  +  +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node2.html b/sag-0.6.1-www/Invisible/sag-0.6/node2.html new file mode 100644 index 0000000..1b9a53e --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node2.html @@ -0,0 +1,168 @@ + + + + +Introduction + + + + + + + + next up previous contents index
+ Next: Typographical conventions +Up: Linux System Administrators' Guide + Previous: Contents +

+

Introduction

+

+

+ + In the beginning, the file was without form, and void; and
+ emptiness was upon the face of the bits. And the Fingers of
+ the Author moved upon the face of the keyboard. And the Author
+ said, Let there be words, and there were words.
+

+

+ This manual, the Linux System Administrators' + Guide, describes the system administration aspects of + using Linux. It is intended for people who know next + to nothing about system administration (as in ``what + is it?''), but who have already mastered at least the + basics of normal usage. This manual also doesn't tell + you how to install Linux; that is described in the + Installation and Getting Started document. See below + for more information about Linux manuals. +

+ System administration is all the things that one has + to do to keep a computer system in a useable shape. + It includes things like backing up files (and restoring + them if necessary), installing new programs, creating + accounts for users (and deleting them when no longer + needed), making certain that the filesystem is not + corrupted, and so on. If a computer were, say, a house, + system administration would be called maintenance, + and would include cleaning, fixing broken windows, + and other such things. System administration is + not called maintenance, because that would be too + simple.gif +

+ The structure of this manual is such that many of the chapters + should be usable independently, so that if you need + information about, say, backups, you can read just that + chapter.gif + This hopefully makes the book easier to use as a + reference manual, and makes it possible to read just a small + part when needed, instead of having to read everything. + However, this manual is first and foremost a + tutorial, and a reference manual only as a lucky coincidence. +

+ This manual is not intended to be used completely by itself. + Plenty of the rest of the Linux documentation is also + important for system administrators. After all, a system + administrator is just a user with special privileges and + duties. A very important resource are the manual pages, which + should always be consulted when a command is not familiar. +

+ While this manual is targeted at Linux, a general principle + has been that it should be useful with other UNIX based + operating systems as well. Unfortunately, since there is so + much variance between different versions of UNIX in + general, and in system administration in particular, there is + little hope to cover all variants. Even covering all + possibilities for Linux is difficult, due to the nature of + its development. +

+ There is no one official Linux distribution, so different + people have different setups, and many people have + a setup they have built up themselves. This book is + not targeted at any one distribution, even though I + use the Debian GNU/Linux system almost exclusively. + When possible, I have tried to point out differences, + and explain several alternatives. +

+ I have tried to describe how things work, rather + than just listing ``five easy steps'' for each task. + This means that there is much information here that is + not necessary for everyone, but those parts are marked + as such and can be skipped if you use a preconfigured + system. Reading everything will, naturally, increase + your understanding of the system and should make using + and administering it more pleasant. +

+ +

+ Like all other Linux related development, the + work was done on a volunteer basis: I did it because I + thought it might be fun and because I felt it should be + done. However, like all volunteer work, there is a limit to + how much effort I have been able to spend, and + also on how much knowledge and experience I have. This means + that the manual is not necessarily as good as it would be if a + wizard had been paid handsomely to write it and had spent a + few years to perfect it. I think, of course, that it is + pretty nice, but be warned. +

+ One particular point where I have cut corners + is that I have not covered very thoroughly many + things that are already well documented in other freely + available manuals. This applies especially to program + specific documentation, such as all the details of using + mkfs) . I only describe the purpose of the program, + and as much of its usage as is necessary for the purposes of + this manual. For further information, I refer the gentle + reader to these other manuals. Usually, all of the referred + to documentation is part of the full Linux documentation + set. +

+ While I have tried to make this manual as good as possible, + I would really like to hear from you if you have any ideas on + how to make it better. Bad language, factual errors, ideas + for new areas to cover, rewritten sections, information about + how various UNIX versions do things, I am interested in + all of it. + My contact information is available via the World Wide + Web at http://www.iki.fi/liw/mail-to-lasu.html. + You need to read this web page to bypass my junkmail filters. +

+ Many people have helped me with this book, directly or indirectly. + I would like to especially thank Matt Welsh for inspiration and + LDP leadership, Andy Oram for + getting me to work again with much-valued feedback, Olaf Kirch + for showing me that it can be done, and Adam Richter at Yggdrasil + and others for showing me that other people can find it interesting + as well. +

+ Stephen Tweedie, H. Peter Anvin, Rémy Card, Theodore + Ts'o, and Stephen Tweedie have let me borrow their + workgif (and thus make the book look thicker and much + more impressive). I am most grateful for this, and + very apologetic for the earlier versions that sometimes + lacked proper attribution. +

+ In addition, I would like to thank Mark Komarinski for sending his + material in 1993 and the many system administration columns + in Linux Journal. They are quite informative and inspirational. +

+ Many useful comments have been sent by a large number + of people. My miniature black hole of an archive + doesn't let me find all their names, but some of them + are, in alphabetical order: Paul Caprioli, Ales Cepek, + Marie-France Declerfayt, Dave Dobson, Olaf Flebbe, Helmut + Geyer, Larry Greenfield and his father, Stephen Harris, + Jyrki Havia, Jim Haynes, York Lam, Timothy Andrew Lister, + Jim Lynch, Michael J. Micek, Jacob Navia, Dan Poirier, + Daniel Quinlan, Jouni K Seppänen, Philippe Steindl, + G.B. Stotte. My apologies to anyone I have forgotten. +

+

next up previous contents index
+ Next: Typographical conventions +Up: Linux System Administrators' Guide + Previous: Contents +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node20.html b/sag-0.6.1-www/Invisible/sag-0.6/node20.html new file mode 100644 index 0000000..f876658 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node20.html @@ -0,0 +1,55 @@ + + + + +Overview of the Directory Tree + + + + + + + + next up previous contents index
+ Next: Background +Up: Linux System Administrators' Guide + Previous: The filesystem layout +

+

Overview of the Directory Tree

+   +

+

+ + Two days later, there was Pooh,
+ sitting on his branch, dangling his
+ legs, and there, beside him, were four
+ pots of honey...
+ (A.A. Milne)
+

+

+ This chapter describes the important parts of a standard + Linux directory tree, based on the FSSTND filesystem + standard. It outlines the normal way of breaking the directory + tree into separate filesystems with different purposes and gives + the motivation behind this particular split. Some alternative + ways of splitting are also described. +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node21.html b/sag-0.6.1-www/Invisible/sag-0.6/node21.html new file mode 100644 index 0000000..c0e68cf --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node21.html @@ -0,0 +1,138 @@ + + + + +Background + + + + + + + + next up previous contents index
+ Next: The root filesystem +Up: Overview of the Directory + Previous: Overview of the Directory +

+

Background

+

+ This chapter is loosely based on the Linux filesystem + standard, FSSTND, version 1.2 (see the bibliography, + [Qui95]), which attempts + to set a standard for how the directory tree in a Linux system + is organized. Such a standard has the advantage that + it will be easier to + write or port software for Linux, and to administer Linux + machines, since everything will be in their usual places. There + is no authority behind the standard that forces anyone to comply + with it, but it has got the support of most, if not all, Linux + distributions. It is not a good idea to break with the FSSTND + without very compelling reasons. The FSSTND attempts to follow + Unix tradition and current trends, making Linux systems familiar + to those with experience with other Unix systems, and vice + versa. +

+ This chapter is not as detailed as the FSSTND. A system + administrator should also read the FSSTND for a complete + understanding. +

+ This chapter does not explain all files in detail. The intention + is not to describe every file, but to give an overview of the + system from a filesystem point of view. Further information on + each file is available elsewhere in this manual or the manual + pages. +

+ The full directory tree is intended to be breakable into smaller + parts, each on its own disk or partition, to accomodate to disk + size limits and to ease backup and other system administration. + The major parts are the root, /usr , /var , and + /home  filesystems (see figure 3.1). + Each part has a different purpose. + The directory tree has been designed so that it works well in a + network of Linux machines which may share some parts of the + filesystems over a read-only device (e.g., a CD-ROM), or + over the network with NFS. +

+

  figure424
+Figure 3.1: Parts of a Unix directory tree. + Dashed lines indicate partition limits.
+

+

+ The roles of the different parts of the directory tree are + described below. +

+ Although the different parts have been called filesystems above, + there is no requirement that they actually be on separate filesystems. + They could easily be kept in a single one if the system is + a small single-user system and the user wants to keep things simple. + The directory tree might also be divided into filesystems differently, + depending on how large the disks are, and how space is allocated + for various purposes. + The important part, though, is that all the standard names + work; even if, say, /var  and /usr  are actually on the + same partition, the names /usr/lib/libc.a  and + /var/adm/messages  must work, for example by moving files + below /var  into /usr/var , and making /var  a symlink + to /usr/var . +

+ The Unix filesystem structure groups files according to purpose, + i.e., all commands are in one place, all data files in another, + documentation in a third, and so on. An alternative would be to + group files files according to the program they belong to, i.e., + all Emacs files would be in one directory, all TeX in another, + and so on. The problem with the latter approach is that it + makes it difficult to share files (the program directory often + contains both static and shareable and changing and + non-shareable files), and sometimes to even find the files + (e.g., manual pages in a huge number of places, and making the + manual page programs find all of them is a maintenance + nightmare). +

+

next up previous contents index
+ Next: The root filesystem +Up: Overview of the Directory + Previous: Overview of the Directory +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node22.html b/sag-0.6.1-www/Invisible/sag-0.6/node22.html new file mode 100644 index 0000000..3c8d1fd --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node22.html @@ -0,0 +1,98 @@ + + + + +The root filesystem + + + + + + + + next up previous contents index
+ Next: The /etc directory +Up: Overview of the Directory + Previous: Background +

+

The root filesystem

+

+ The root filesystem should generally be small, since it contains + very critical files and a small, infrequently modified + filesystem has a better chance of not getting corrupted. A + corrupted root filesystem will generally mean that the system + becomes unbootable except with special measures (e.g., from a + floppy), so you don't want to risk it. +

+ The root directory generally doesn't contain any files, except + perhaps the standard boot image for the system, usually called + /vmlinuz . All other files are in subdirectories in the + root filesystems: +

/bin  +
+ Commands needed during bootup that might be used + by normal users (probably after bootup). +
/sbin  +
+ Like /bin , but the commands are not intended + for normal users, although they may use them if necessary + and allowed. +
/etc  +
+ Configuration files specific to the machine. +
/root  +
+ The home directory for user root. +
/lib  +
+ Shared libraries needed by the programs on the root + filesystem. +
/lib/modules  +
+ Loadable kernel modules, especially those that are needed + to boot the system when recovering from disasters (e.g., + network and filesystem drivers). +
/dev  +
+ Device files. +
/tmp  +
+ Temporary files. Programs running after bootup should + use /var/tmp , not /tmp , since the former + is probably on a disk with more space. +
/boot  +
+ Files used by the bootstrap loader, e.g., LILO. Kernel + images are often kept here instead of in the root + directory. If there are many kernel images, the directory + can easily grow rather big, and it might be better to + keep it in a separate filesystem. Another reason would + be to make sure the kernel images are within the first + 1024 cylinders of an IDE disk. +
/mnt  +
+ Mount point for temporary mounts by the system administrator. + Programs aren't supposed to mount on /mnt  automatically. + /mnt  might be divided into subdirectories (e.g., + /mnt/dosa  might be the floppy drive using an MS-DOS + filesystem, and /mnt/exta  might be the same with an ext2 + filesystem). +
/proc , /usr , /var , /home  +
+ Mount points for the other filesystems. +

+


+ +
next up previous contents index
+ Next: The /etc directory +Up: Overview of the Directory + Previous: Background +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node23.html b/sag-0.6.1-www/Invisible/sag-0.6/node23.html new file mode 100644 index 0000000..609e3c3 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node23.html @@ -0,0 +1,153 @@ + + + + +The /etc directory + + + + + + + + next up previous contents index
+ Next: The /dev directory +Up: The root filesystem + Previous: The root filesystem +

+ 

The /etc directory

+

+ The /etc  directory contains a lot of files. Some of them + are described below. For others, you should determine which + program they belong to and read the manual page for that program. + Many networking configuration files are in /etc  as well, + and are described in the Networking Administrators' Guide. +

/etc/rc  or /etc/rc.d  or /etc/rc?.d  +
+ Scripts or directories of scripts to run at startup or when + changing the run level. + See the chapter on init  for further information. +

+

/etc/passwd  +
+ The user database, with fields giving the username, real name, + home directory, encrypted password, and other information about + each user. The format is documented in the passwd  + manual page. +

+

/etc/fdprm  +
+ Floppy disk parameter table. Describes what different floppy + disk formats look like. Used by setfdprm . See + the setfdprm  manual page for more information. +

+

/etc/fstab  +
+ Lists the filesystems mounted automatically at startup + by the mount -a command (in /etc/rc  or equivalent + startup file). Under Linux, also contains information about swap + areas used automatically by swapon -a. + See section 4.8.5 and the + mount  manual page for more information. +

+

/etc/group  +
+ Similar to /etc/passwd , but describes + groups instead of users. See the group  manual page for + more information. +

+

/etc/inittab  +
+ Configuration file for init . +

+

/etc/issue  +
+ Output by getty  before the login prompt. Usually contains + a short description or welcoming message to the system. The + contents are up to the system administrator. +

+

/etc/magic  +
+ The configuration file for file . Contains + the descriptions of various file formats based on which + file  guesses the type of the file. See the magic  + and file  manual pages for more information. +

+

/etc/motd  +
+ The message of the day, automatically output after + a successful login. Contents are up to the system administrator. + Often used for getting information to every user, such as + warnings about planned downtimes. +

+

/etc/mtab  +
+ List of currently mounted filesystems. Initially set up by + the scripts, and updated automatically by the mount  command. + Used when a list of mounted filesystems is needed, e.g., by + the df  command. +

+

/etc/shadow  +
+ Shadow password file on systems with shadow password software + installed. Shadow passwords move the encrypted password from + /etc/passwd  into /etc/shadow ; the latter is not + readable by anyone except root. This makes it harder + to crack passwords. +

+

/etc/login.defs  +
+ Configuration file for the login  command. +

+

/etc/printcap  +
+ Like /etc/termcap , but intended for printers. Different + syntax. +

+

/etc/profile , /etc/csh.login , /etc/csh.cshrc  +
+ Files executed at login or startup time by the Bourne or + C shells. These allow the system administrator to set global + defaults for all users. + See the manual pages for the respective shells. +

+

/etc/securetty  +
+ Identifies secure terminals, i.e., the terminals from which + root is allowed to log in. + Typically only the virtual + consoles are listed, so that it becomes impossible (or at + least harder) to gain superuser privileges by breaking into a + system over a modem or a network. +

+

/etc/shells  +
+ Lists trusted shells. The chsh  command allows users + to change their login shell only to shells listed in this + file. ftpd , the server process that provides FTP + services for a machine, will check that the user's shell is + listed in /etc/shells  and will not let people log in + unles the shell is listed there. +

+

/etc/termcap  +
+ The terminal capability database. Describes by what ``escape + sequences'' various terminals can be controlled. Programs are + written so that instead of directly outputting an escape + sequence that only works on a particular brand of terminal, + they look up the correct sequence to do whatever it is they + want to do in /etc/termcap . As a result most programs + work with most kinds of terminals. See the + termcap , curs_termcap , and terminfo  + manual pages for more information. +

+

next up previous contents index
+ Next: The /dev directory +Up: The root filesystem + Previous: The root filesystem +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node24.html b/sag-0.6.1-www/Invisible/sag-0.6/node24.html new file mode 100644 index 0000000..8f9f69f --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node24.html @@ -0,0 +1,36 @@ + + + + +The /dev directory + + + + + + + + next up previous contents index
+ Next: The /usr filesystem +Up: The root filesystem + Previous: The /etc directory +

+ 

The /dev directory

+

+ The /dev  directory contains the special device files for + all the devices. The device files are named using special + conventions; these are described in the Device list (see [Anv]). + The device files are created during installation, and later with + the /dev/MAKEDEV  script. The /dev/MAKEDEV.local  is + a script written by the system administrator that creates local-only + device files or links (i.e., those that are not part of the + standard MAKEDEV , such as device files for some non-standard + device driver). +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node25.html b/sag-0.6.1-www/Invisible/sag-0.6/node25.html new file mode 100644 index 0000000..aedc858 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node25.html @@ -0,0 +1,73 @@ + + + + +The /usr filesystem + + + + + + + + next up previous contents index
+ Next: The /var filesystem +Up: Overview of the Directory + Previous: The /dev directory +

+ 

The /usr filesystem

+

+ The /usr  filesystem is often large, since all programs + are installed there. All files in /usr  usually come from + a Linux distribution; locally installed programs and other + stuff goes below /usr/local . This makes it possible to + update the system from a new version of the distribution, or even + a completely new distribution, without having to install all programs + again. + Some of the subdirectories of /usr  are listed below (some of + the less important directories have been dropped; see the FSSTND + for more information). +

/usr/X11R6  +
+ The X Window System, all files. To simplify the development + and installation of X, the X files have not been + integrated into the rest of the system. There is a + directory tree below /usr/X11R6  similar to that below + /usr  itself. +
/usr/X386  +
+ Similar to /usr/X11R6 , but for X11 Release 5. +
/usr/bin  +
+ Almost all user commands. Some commands are in + /bin  or in /usr/local/bin . +
/usr/sbin  +
+ System administration commands that are not needed on + the root filesystem, e.g., most server programs. +
/usr/man , /usr/info , /usr/doc  +
+ Manual pages, GNU Info documents, and miscellaneous + other documentation files, respectively. +
/usr/include  +
+ Header files for the C programming language. This should + actually be below /usr/lib  for consistency, but + the tradition is overwhelmingly in support for this name. +
/usr/lib  +
+ Unchanging data files for programs and subsystems, including + some site-wide configuration files. The name lib + comes from library; originally libraries of programming + subroutines were stored in /usr/lib . +
/usr/local  +
+ The place for locally installed software and other files. +

+


+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node26.html b/sag-0.6.1-www/Invisible/sag-0.6/node26.html new file mode 100644 index 0000000..0a1508c --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node26.html @@ -0,0 +1,88 @@ + + + + +The /var filesystem + + + + + + + + next up previous contents index
+ Next: The /proc filesystem +Up: Overview of the Directory + Previous: The /usr filesystem +

+ 

The /var filesystem

+

+ The /var  contains data that is changed when the system is + running normally. It is specific for each system, i.e., not + shared over the network with other computers. +

/var/catman  +
+ A cache for man pages that are formatted on demand. + The source for manual pages is usually stored in + /usr/man/man* ; some manual pages might come with + a pre-formatted version, which is stored in /usr/man/cat* . + Other manual pages need to be formatted when they are + first viewed; the formatted version is then stored + in /var/man  so that the next person to view the + same page won't have to wait for it to be formatted. + (/var/catman  is often cleaned in the same way + temporary directories are cleaned.) +
/var/lib  +
+ Files that change while the system is running normally. +
/var/local  +
+ Variable data for programs that are installed in + /usr/local  (i.e., programs that have been installed + by the system administrator). Note that even locally + installed programs should use the other /var  directories + if they are appropriate, e.g., /var/lock . +
/var/lock  +
+ Lock files. Many programs follow a convention to + create a lock file in /var/lock  to indicate that + they are using a particular device or file. Other + programs will notice the lock file and won't attempt + to use the device or file. +
/var/log  +
+ Log files from various programs, especially login  + (/var/log/wtmp , which logs all logins and logouts + into the system) and syslog  (/var/log/messages , + where all kernel and system program message are usually + stored). Files in /var/log  can often grow indefinitely, + and may require cleaning at regular intervals. +
/var/run  +
+ Files that contain information about the system that is + valid until the system is next booted. For example, + /var/run/utmp  contains information about people + currently logged in. +
/var/spool  +
+ Directories for mail, news, printer queues, and other + queued work. Each different spool has its own + subdirectory below /var/spool , e.g., the mailboxes + of the users are in /var/spool/mail . +
/var/tmp  +
+ Temporary files that are large or that need to exist + for a longer time than what is allowed for /tmp . + (Although the system administrator might not allow + very old files in /var/tmp  either.) +

+

next up previous contents index
+ Next: The /proc filesystem +Up: Overview of the Directory + Previous: The /usr filesystem +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node27.html b/sag-0.6.1-www/Invisible/sag-0.6/node27.html new file mode 100644 index 0000000..a0c8c03 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node27.html @@ -0,0 +1,118 @@ + + + + +The /proc filesystem + + + + + + + + next up previous contents index
+ Next: Using Disks and Other +Up: Overview of the Directory + Previous: The /var filesystem +

+ 

The /proc filesystem

+

+ The /proc  filesystem contains a illusionary filesystem. + It does not exist on a disk. Instead, the kernel creates it + in memory. It is used to provide information about the + system (originally about processes, hence the name). Some + of the more important files and directories are explained + below. The /proc  filesystem is described in more detail + in the proc  manual page. +

/proc/1  +
+ A directory with information about process number 1. + Each process has a directory below /proc  with + the name being its process identification number. +
/proc/cpuinfo  +
+ Information about the processor, such as its type, make, + model, and perfomance. +
/proc/devices  +
+ List of device drivers configured into the currently + running kernel. +
/proc/dma  +
+ Shows which DMA channels are being used at the moment. +
/proc/filesystems  +
+ Filesystems configured into the kernel. +
/proc/interrupts  +
+ Shows which interrupts are in use, and how many of each + there have been. +
/proc/ioports  +
+ Which I/O ports are in use at the moment. +
/proc/kcore  +
+ An image of the physical memory of the system. This + is exactly the same size as your physical memory, but + does not really take up that much memory; it is generated + on the fly as programs access it. (Remember: unless you + copy it elsewhere, nothing under /proc  takes up + any disk space at all.) +
/proc/kmsg  +
+ Messages output by the kernel. These are also routed + to syslog . +
/proc/ksyms  +
+ Symbol table for the kernel. +
/proc/loadavg  +
+ The `load average' of the system; three meaningless + indicators of how much work the system has to do at + the moment. +
/proc/meminfo  +
+ Information about memory usage, both physical and swap. +
/proc/modules  +
+ Which kernel modules are loaded at the moment. +
/proc/net  +
+ Status information about network protocols. +
/proc/self  +
+ A symbolic link to the process directory of the program + that is looking at /proc . When two processes look + at /proc , they get different links. This is mainly + a convenience to make it easier for programs to get + at their process directory. +
/proc/stat  +
+ Various statistics about the system, such as the number + of page faults since the system was booted. +
/proc/uptime  +
+ The time the system has been up. +
/proc/version  +
+ The kernel version. +

+

+ Note that while the above files tend to be easily readable text + files, they can sometimes be formatted in a way that is not + easily digestable. There are many commands that do little more + than read the above files and format them for easier understanding. + For example, the free  program reads /proc/meminfo  + and converts the amounts given in bytes to kilobytes (and adds + a little more information, as well). +

+

next up previous contents index
+ Next: Using Disks and Other +Up: Overview of the Directory + Previous: The /var filesystem +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node28.html b/sag-0.6.1-www/Invisible/sag-0.6/node28.html new file mode 100644 index 0000000..d9eb402 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node28.html @@ -0,0 +1,117 @@ + + + + +Using Disks and Other Storage Media + + + + + + + + next up previous contents index
+ Next: Two kinds of devices +Up: Linux System Administrators' Guide + Previous: The /proc filesystem +

+

Using Disks and Other Storage Media

+

+

+ + On a clear disk you can seek forever.
+

+

+ When you install or upgrade your system, you need to do a fair + amount of work on your disks. You have to make filesystems on + your disks so that files can be + stored on them and reserve space for the different parts of + your system. +

+ This chapter explains all these initial activities. Usually, + once you get your system set up, you won't have to go through + the work again, except for using floppies. You'll need to come + back to this chapter if you add a new disk or want to fine-tune + your disk usage. +

+ The basic tasks in administering disks are: +

+

+ Chapter 5 contains information about virtual memory + and disk caching, of which you also need to be aware when using + disks. +

+ This chapter explains what you need to know for hard disks, + floppies, CD-ROM's, and tape drives. +

+

+ +
next up previous contents index
+ Next: Two kinds of devices +Up: Linux System Administrators' Guide + Previous: The /proc filesystem +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node29.html b/sag-0.6.1-www/Invisible/sag-0.6/node29.html new file mode 100644 index 0000000..6d65ed2 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node29.html @@ -0,0 +1,83 @@ + + + + +Two kinds of devices + + + + + + + + next up previous contents index
+ Next: Hard disks +Up: Using Disks and Other + Previous: Using Disks and Other +

+

Two kinds of devices

+

+ UNIX, and therefore Linux, recognizes two different + kinds of device: random-access block devices (such as disks), + and character devices (such as tapes and serial lines), + some of which may be serial, and some random-access. Each + supported device is represented in the filesystem as a + device file. When you read or write a device file, the + data comes from or goes to the device it represents. This way + no special programs (and no special application programming + methodology, such as catching interrupts or polling a serial + port) are necessary to access devices; for example, to send a + file to the printer, one could just say +

+$ cat filename > /dev/lp1
+$ +
+ and the contents of the file are printed (the file must, of + course, be in a form that the printer understands). However, + since it is not a good idea to have several people cat their + files to the printer at the same time, one usually uses a special + program to send the files to be printed (usually lpr ). + This program makes sure that only one file is being printed + at a time, and will automatically send files to the printer as + soon as it finishes with the previous file. Something similar + is needed for most devices. In fact, one seldom needs to worry + about device files at all. +

+ Since devices show up as files in the filesystem (in the + /dev  directory), it is easy + to see just what device files exist, using ls  or + another suitable command. In the output of ls -l , the + first column contains the type of the file and its + permissions. For example, inspecting a serial device + gives on my system +

+$ ls -l /dev/cua0
+crw-rw-rw- 1 root uucp 5, 64 Nov 30 1993 /dev/cua0
+$ +
+ The first character in the first column, i.e., `c' in + crw-rw-rw- above, tells an informed user the type of the file, + in this case a character device. For + ordinary files, the first character is `-', for + directories it is `d', and for block devices `b'; + see the ls  man page for further information. +

+ Note that usually all device files exist even though the + device itself might be not be installed. So just because you + have a file /dev/sda , it doesn't mean that you really do + have an SCSI hard disk. + Having all the device files makes the installation programs + simpler, and makes it easier to add new hardware (there is no + need to find out the correct parameters for and create the device + files for the new device). +

+

next up previous contents index
+ Next: Hard disks +Up: Using Disks and Other + Previous: Using Disks and Other +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node3.html b/sag-0.6.1-www/Invisible/sag-0.6/node3.html new file mode 100644 index 0000000..6cf9bd3 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node3.html @@ -0,0 +1,54 @@ + + + + +Typographical conventions + + + + + + + + next up previous contents index
+ Next: The Linux Documentation Project +Up: Introduction + Previous: Introduction +

+

Typographical conventions

+

+

Bold +
Used to mark new concepts, WARNINGS, +and keywords in a language. +

+

italics +
Used for emphasis in text, and +occasionally for quotes or introductions at the beginning of a section. +

+

slanted +
Used to mark meta-variables in the text, +especially in representations of the command line. For example, +
ls -l foo
+where foo would ``stand for'' a filename, such as /bin/cp. +

+

Typewriter +
Used to represent screen interaction, as in +
$ ls -l /bin/cp
+-rwxr-xr-x  1 root    wheel    12104 Sep 25 15:53 /bin/cp
+

+Also used for code examples, whether it is C code, a shell script, or +something else, and to display general files, such as configuration +files. When necessary for clarity's sake, these examples or figures +will be enclosed in thin boxes. +

+

Key +
Represents a key to press. You will often see it +in this form: +
Press Return to continue.
+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node30.html b/sag-0.6.1-www/Invisible/sag-0.6/node30.html new file mode 100644 index 0000000..49dc7ab --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node30.html @@ -0,0 +1,150 @@ + + + + +Hard disks + + + + + + + + next up previous contents index
+ Next: Floppies +Up: Using Disks and Other + Previous: Two kinds of devices +

+

Hard disks

+

+ This subsection introduces terminology related to hard disks. + If you already know the terms and concepts, you can skip this + subsection. +

+ See figure 4.1 for a schematic picture of the + important parts in a hard disk. A hard disk consists of one or + more circular platters,gif of which either or both surfaces are coated with a + magnetic substance used for recording the data. For each + surface, there is a read-write head that examines or + alters the recorded data. The platters rotate on a common axis; + a typical rotation speed is 3600 rotations per minute, + although high-performance hard disks have higher speeds. The + heads move along the radius of the platters; this movement + combined with the rotation of the platters allows the head to + access all parts of the surfaces. +

+ The processor (CPU) and the actual disk communicate through + a disk controller. This relieves the rest of the computer + from knowing how to use the drive, since the controllers for + different types of disks can be made to use the same interface towards + the rest of the computer. Therefore, the computer can say just + ``hey disk, gimme what I want'', instead of a long and complex + series of electric signals to move the head to the proper location + and waiting for the correct position to come under the head + and doing all the + other unpleasant stuff necessary. (In reality, the interface + to the controller is still complex, but much less so than it would + otherwise be.) The controller can also do some other stuff, + such as caching, or automatic bad sector replacement. +

+ The above is usually all one needs to understand about the + hardware. There is also a bunch of other stuff, such as the + motor that rotates the platters and moves the heads, and the + electronics that control the operation of the mechanical + parts, but that is mostly not relevant for understanding the + working principle of a hard disk. +

+ The surfaces are usually divided into concentric rings, called + tracks, and these in turn are divided into sectors. + This division is used to specify locations + on the hard disk and to allocate disk space to files. To find + a given place on the hard disk, one might say ``surface 3, + track 5, sector 7''. Usually the number of sectors is the + same for all tracks, but some hard disks put more sectors in + outer tracks (all sectors are of the same physical size, so + more of them fit in the longer outer tracks). Typically, a + sector will hold 512 bytes of data. The disk itself can't + handle smaller amounts of data than one sector. +

+

  figure1034
+Figure 4.1: A schematic picture of a hard disk.
+

+

+ Each surface is divided into tracks (and sectors) in the same + way. This means that when the head for one surface is on a + track, the heads for the other surfaces are also on the + corresponding tracks. All the corresponding tracks taken + together are called a cylinder. It takes time to move + the heads from one track (cylinder) to another, so by placing + the data that is often accessed together (say, a file) so that + it is within one cylinder, it is not necessary to move the + heads to read all of it. This improves performance. It is + not always possible to place files like this; files that are + stored in several places on the disk are called fragmented. +

+ The number of surfaces (or heads, which is the same thing), + cylinders, and sectors vary a lot; the specification of the + number of each is called the geometry of a hard disk. The + geometry is usually stored in a special, battery-powered memory + location called the CMOS RAM, from where the operating + system can fetch it during bootup or driver initialization. +

+ Unfortunately, the BIOSgif has a design limitation, which makes it + impossible to specify a track number that is larger than 1024 in + the CMOS RAM, + which is too little for a large hard disk. To overcome this, + the hard disk controller lies about the geometry, and + translates the addresses given by the computer into something + that fits reality. For example, a hard disk might have 8 heads, + 2048 tracks, and 35 sectors per trackgif. Its controller could lie to the + computer and claim that it has 16 heads, 1024 tracks, and 35 + sectors per track, thus not exceeding the limit on tracks, and + translates the address that the computer gives it by halving the + head number, and doubling the track number. The math can be + more complicated in reality, because the numbers are not as nice + as here (but again, the details are not relevant for + understanding the principle). This translation distorts the + operating system's view of how the disk is organized, thus making it + impractical to use the all-data-on-one-cylinder trick to boost + performance. +

+ The translation is only a problem for IDE disks. SCSI disks + use a sequential sector number (i.e., the controller translates + a sequential sector number to a head, cylinder, and sector + triplet), and a completely different method for the CPU to talk + with the controller, so they are insulated from the problem. + Note, however, that the computer might not know the real geometry + of an SCSI disk either. +

+ Since Linux often will not know the real geometry of a disk, + its filesystems don't even try to keep files within a single cylinder. + Instead, it tries to assign sequentially numbered sectors to + files, which almost always gives similar performance. The issue + is further complicated by on-controller caches, and automatic + prefetches done by the controller. +

+ Each hard disk is represented by a separate device file. + There can (usually) be only two or four IDE hard disks. + These are known as /dev/hda , /dev/hdb , + /dev/hdc , and /dev/hdd , respectively. SCSI + hard disks are known as /dev/sda , /dev/sdb , and + so on. Similar naming conventions exist for other hard + disk types; see [Anv] for more information. + Note that the device files for the hard disks give access + to the entire disk, with no regard to partitions (which + will be discussed below), and it's easy to mess up the + partitions or the data in them if you aren't careful. + The disks' device files are usually used only to get + access to the master boot record (which will also be + discussed below). +

+

next up previous contents index
+ Next: Floppies +Up: Using Disks and Other + Previous: Two kinds of devices +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node31.html b/sag-0.6.1-www/Invisible/sag-0.6/node31.html new file mode 100644 index 0000000..473e354 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node31.html @@ -0,0 +1,86 @@ + + + + +Floppies + + + + + + + + next up previous contents index
+ Next: CD-ROM's +Up: Using Disks and Other + Previous: Hard disks +

+

Floppies

+

+ A floppy disk consists of a flexible membrane covered on one + or both sides with similar magnetic substance as a hard disk. + The floppy disk itself doesn't have a read-write head, that is + included in the drive. A floppy corresponds to one platter in + a hard disk, but is removable and one drive can be used to + access different floppies, whereas the hard disk is one + indivisible unit. +

+ Like a hard disk, a floppy is divided into tracks and sectors + (and the two corresponding tracks on either side of a floppy + form a cylinder), but there are many fewer of them than on a + hard disk. +

+ A floppy drive can usually use several different types of disks; + for example, a 3.5 inch drive can use both 720 kB and + 1.44 MB disks. Since the drive has to operate a bit differently + and the operating system must know how big the disk is, there + are many device files for floppy drives, one per combination of + drive and disk type. + Therefore, /dev/fd0H1440  is the first floppy drive (fd0), + which must be a 3.5 inch drive, + using a 3.5 inch, high density disk (H) of + size 1440 kB (1440), i.e., a normal 3.5 inch HD floppy. + For more information on the naming conventions for the floppy + devices, see [Anv]. +

+ The names for floppy drives are complex, however, and Linux + therefore has a special floppy device type that automatically + detects the type of the disk in the drive. It works by trying + to read the first sector of a newly inserted floppy using different + floppy types until it finds the correct one. This naturally requires + that the floppy is formatted first. The automatic devices are + called /dev/fd0 , /dev/fd1 , and so on. +

+ The parameters the automatic device uses to access a disk can + also be set using the program setfdprm . This can be + useful if you need to use disks that do not follow any usual + floppy sizes, e.g., if they have an unusual number of sectors, + or if the autodetecting for some reason fails and the proper + device file is missing. +

+ Linux can handle many nonstandard floppy disk formats in + addition to all the standard ones. Some of these require + using special formatting programs. + We'll skip these disk types for now, but in the mean time + you can examine the /etc/fdprm  file. It specifies + the settings that setfdprm  recognizes. +

+ The operating system must know when a disk has been changed in + a floppy drive, for example, in order to avoid using cached + data from the previous disk. Unfortunately, the signal line + that is used for this is sometimes broken, and worse, this won't + always be noticeable when using the drive from within MS-DOS. + If you are experiencing weird problems using floppies, this might + be the reason. The only way to correct it is to repair the + floppy drive. +

+

next up previous contents index
+ Next: CD-ROM's +Up: Using Disks and Other + Previous: Hard disks +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node32.html b/sag-0.6.1-www/Invisible/sag-0.6/node32.html new file mode 100644 index 0000000..906fe80 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node32.html @@ -0,0 +1,81 @@ + + + + +CD-ROM's + + + + + + + + next up previous contents index
+ Next: Tapes +Up: Using Disks and Other + Previous: Floppies +

+

CD-ROM's

+

+ A CD-ROM drive uses an optically read, plastic coated disk. + The information is recorded on the surface of the + diskgif in small `holes' + aligned along a spiral from the center to the edge. The + drive directs a laser beam along the spiral to read the disk. + When the laser hits a hole, the laser is reflected in one way; + when it hits smooth surface, it is reflected in another way. + This makes it easy to code bits, and therefore information. + The rest is easy, mere mechanics. +

+ CD-ROM drives are slow compared to hard disks. Whereas a + typical hard disk will have an average seek time less than + 15 milliseconds, a fast CD-ROM drive can use tenths of a second + for seeks. The actual data transfer rate is fairly high at + hundreds of kilobytes per second. The slowness means that + CD-ROM drives are not as pleasant to use instead of hard disks + (some Linux distributions provide `live' filesystems on CD-ROM's, + making it unnecessary to copy the files to the hard disk, making + installation easier and saving a lot of hard disk space), although + it is still possible. For installing new software, CD-ROM's are + very good, since it maximum speed is not essential during + installation. +

+ There are several ways to arrange data on a CD-ROM. The most + popular one is specified by the international standard ISO 9660. + This standard specifies a very minimal filesystem, which is + even more crude than the one MS-DOS uses. On the other hand, + it is so minimal that every operating system should be able to + map it to its native system. +

+ For normal UNIX use, the ISO 9660 filesystem is not usable, so + an extension to the standard has been developed, called + the Rock Ridge extension. Rock Ridge allows longer filenames, + symbolic links, and a lot of other goodies, making a CD-ROM + look more or less like any contemporary UNIX filesystem. + Even better, a Rock Ridge filesystem is still a valid ISO 9660 + filesystem, making it usable by non-UNIX systems as well. + Linux supports both ISO 9660 and the Rock Ridge extensions; + the extensions are recognized and used automatically. +

+ The filesystem is only half the battle, however. Most CD-ROM's + contain data that requires a special program to access, and + most of these programs do not run under Linux (except, possibly, + under dosemu, the Linux MS-DOS emulator). +

+ A CD-ROM drive is accessed via the corresponding device file. + There are several ways to connect a CD-ROM drive to the computer: + via SCSI, via a sound card, or via EIDE. The hardware hacking + needed to do this is outside the scope of this book, but the + type of connection decides the device file. See [Anv] + for enlightment. +

+

next up previous contents index
+ Next: Tapes +Up: Using Disks and Other + Previous: Floppies +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node33.html b/sag-0.6.1-www/Invisible/sag-0.6/node33.html new file mode 100644 index 0000000..8ada116 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node33.html @@ -0,0 +1,40 @@ + + + + +Tapes + + + + + + + + next up previous contents index
+ Next: Formatting +Up: Using Disks and Other + Previous: CD-ROM's +

+

Tapes

+

+ A tape drive uses a tape, similargif to cassettes used for music. A tape is + serial in nature, which means that in order to get to any given + part of it, you first have to go through all the parts in between. + A disk can be accessed randomly, i.e., you can jump directly + to any place on the disk. The serial access of tapes makes them + slow. +

+ On the other hand, tapes are relatively cheap to make, + since they do not need to be fast. They can also easily be made + quite long, and can therefore contain a large amount of data. + This makes tapes very suitable for things like archiving and + backups, which do not require large speeds, but benefit from + low costs and large storage capacities. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node34.html b/sag-0.6.1-www/Invisible/sag-0.6/node34.html new file mode 100644 index 0000000..881fcbc --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node34.html @@ -0,0 +1,151 @@ + + + + +Formatting + + + + + + + + next up previous contents index
+ Next: Partitions +Up: Using Disks and Other + Previous: Tapes +

+

Formatting

+

+ Formatting is the process of writing marks on the + magnetic media that are used to mark tracks and sectors. + Before a disk is formatted, its magnetic surface is a complete + mess of magnetic signals. When it is formatted, some order is + brought into the chaos by essentially drawing lines where the + tracks go, and where they are divided into sectors. The + actual details are not quite exactly like this, but that is + irrelevant. What is important is that a disk cannot be used + unless it has been formatted. +

+ The terminology is a bit confusing here: in MS-DOS, the word + formatting is used to cover also the process of creating a + filesystem (which will be discussed below). There, the two + processes are often combined, especially for floppies. When + the distinction needs to be made, the real formatting is + called low-level formatting, while making the filesystem + is called high-level formatting. In UNIX circles, + the two are called formatting and making a filesystem, so + that's what is used in this book as well. +

+ For IDE and some SCSI disks the formatting is actually + done at the factory and doesn't need to be repeated; hence + most people rarely need to worry about it. In fact, + formatting a hard disk can cause it to work less well, for + example because a disk might need to be formatted in some very + special way to allow automatic bad sector replacement to work. +

+ Disks that need to be or can be formatted often require a special + program anyway, because the interface to the formatting logic + inside the drive is different from drive to drive. The + formatting program is often either on the controller BIOS, or + is supplied as an MS-DOS program; neither of these can easily be used + from within Linux. +

+ During formatting one might encounter bad spots on the disk, + called bad blocks or bad sectors. These are sometimes + handled by the drive itself, + but even then, if more of them develop, something needs to be + done to avoid using those parts of the disk. The logic to do + this is built into the filesystem; how to add the information + into the filesystem is described below. Alternatively, one + might create a small partition that covers just the bad part + of the disk; this approach might be a good idea if the bad + spot is very large, since filesystems can sometimes have + trouble with very large bad areas. +

+ Floppies are formatted with fdformat . The floppy device + file to use is given as the parameter. For example, the + following command would format a high density, + 3.5 inch floppy in the first floppy drive: +

+$ fdformat /dev/fd0H1440
+Double-sided, 80 tracks, 18 sec/track. Total capacity 1440 kB.
+Formatting ... done
+Verifying ... done
+$ +
+ Note that if you want to use an autodetecting device (e.g., + /dev/fd0 ), you must set the parameters of the device + with setfdprm  first. To achieve the same effect as + above, one would have to do the following: +
+$ setfdprm /dev/fd0 1440/1440
+$ fdformat /dev/fd0
+Double-sided, 80 tracks, 18 sec/track. Total capacity 1440 kB.
+Formatting ... done
+Verifying ... done
+$ +
+ It is usually more convenient to choose the correct device file + that matches the type of the floppy. Note that it is unwise to + format floppies to contain more information than what they are + designed for. +

+ fdformat  will also validate the floppy, i.e., check it + for bad blocks. It will try a bad block several times (you + can usually hear this, the drive noise changes dramatically). + If the floppy is only marginally bad (due to dirt on the + read/write head, some errors are false signals), fdformat  won't + complain, but a real error will abort the validation process. + The kernel will print log messages for each I/O error it + finds; these will go to the console or, if syslog  + is being used, to the file /usr/adm/messages . fdformat  + itself won't tell where the error is (one usually doesn't care, + floppies are cheap enough that a bad one is automatically thrown + away). +

+$ fdformat /dev/fd0H1440
+Double-sided, 80 tracks, 18 sec/track. Total capacity 1440 kB.
+Formatting ... done
+Verifying ... read: Unknown error
+$ +
+

+ The badblocks  command can be used to search any disk or + partition for bad blocks (including a floppy). It does not + format the disk, so it can be used to check even existing + filesystems. The example below checks a 3.5 inch + floppy with two bad blocks. +

+$ badblocks /dev/fd0H1440 1440
+718
+719
+$ +
+ badblocks  outputs the block numbers of the bad blocks it finds. + Most filesystems can avoid such bad blocks. They maintain a list + of known bad blocks, which is initialized when the filesystem is + made, and can be modified later. The initial search for bad + blocks can be done by the mkfs  command (which initializes + the filesystem), but later checks should be done with + badblocks  and the new blocks should be added with + fsck . We'll describe mkfs  and fsck  later. +

+ Many modern disks automatically notice bad blocks, and attempt + to fix them by using a special, reserved good block instead. + This is invisible to the operating system. This feature should + be documented in the disk's manual, if you're curious if it + is happening. Even such disks can fail, if the number of bad + blocks grows too large, although chances are that by then the disk + will be so rotten as to be unusable. +

+

next up previous contents index
+ Next: Partitions +Up: Using Disks and Other + Previous: Tapes +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node35.html b/sag-0.6.1-www/Invisible/sag-0.6/node35.html new file mode 100644 index 0000000..5b24447 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node35.html @@ -0,0 +1,51 @@ + + + + +Partitions + + + + + + + + next up previous contents index
+ Next: The MBRboot sectors +Up: Using Disks and Other + Previous: Formatting +

+

Partitions

+

+ A hard disk can be divided into several partitions. + Each partition functions as if it were a separate hard disk. + The idea is that if you have one hard disk, and want to have, + say, two operating systems on it, you can divide the disk into + two partitions. Each operating system uses its partition as + it wishes and doesn't touch the other one's. This way the two + operating systems can co-exist peacefully on the same hard + disk. Without partitions one would have to buy a hard disk for + each operating system. +

+ Floppies are not partitioned. There is no technical reason + against this, but since they're so small, partitions would be + useful only very rarely. CD-ROM's are usually also not + partitioned, since it's easier to use them as one big + disk, and there is seldom a need to have several operating + systems on one. +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node36.html b/sag-0.6.1-www/Invisible/sag-0.6/node36.html new file mode 100644 index 0000000..788a4f5 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node36.html @@ -0,0 +1,74 @@ + + + + +The MBR, boot sectors and partition table + + + + + + + + next up previous contents index
+ Next: Extended and logical partitions +Up: Partitions + Previous: Partitions +

+

The MBR, boot sectors and partition table

+

+ The information about how a hard disk has been partitioned is + stored in its first sector (that is, the first sector of the + first track on the first disk surface). The first sector is the + master boot record (MBR) of the disk; this is the sector + that the BIOS reads in and starts when the machine is first + booted. The master boot record contains a small program that + reads the partition table, checks which partition is active + (that is, marked bootable), and reads the first sector of that + partition, the partition's boot sector (the MBR is also a + boot sector, but it has a special status and therefore a special + name). This boot sector contains another small program that + reads the first part of the operating system stored on that + partition (assuming it is bootable), and then starts it. +

+ The partitioning scheme is not built into the hardware, or + even into the BIOS. It is only a convention that many + operating systems follow. Not all operating systems do follow + it, but they are the exceptions. Some operating + systems support partitions, but they occupy one partition on + the hard disk, and use their internal partitioning method + within that partition. The latter type exists peacefully + with other operating systems (including Linux), and does not + require any special measures, but an operating system + that doesn't support partitions cannot co-exist on the same + disk with any other operating system. +

+ As a safety precaution, it is a good idea to write down the + partition table on a piece of paper, so that if it ever corrupts + you don't have to lose all your files. (A bad partition table + can be fixed with fdisk ). The relevant information + is given by the fdisk -l  command: +

+$ fdisk -l /dev/hda
+
+Disk /dev/hda: 15 heads, 57 sectors, 790 cylinders
+Units = cylinders of 855 * 512 bytes
+
+ Device Boot Begin Start End Blocks Id System
+/dev/hda1 1 1 24 10231+ 82 Linux swap
+/dev/hda2 25 25 48 10260 83 Linux native
+/dev/hda3 49 49 408 153900 83 Linux native
+/dev/hda4 409 409 790 163305 5 Extended
+/dev/hda5 409 409 744 143611+ 83 Linux native
+/dev/hda6 745 745 790 19636+ 83 Linux native
+$ +
next up previous contents index
+ Next: Extended and logical partitions +Up: Partitions + Previous: Partitions +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node37.html b/sag-0.6.1-www/Invisible/sag-0.6/node37.html new file mode 100644 index 0000000..843dc3e --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node37.html @@ -0,0 +1,53 @@ + + + + +Extended and logical partitions + + + + + + + + next up previous contents index
+ Next: Partition types +Up: Partitions + Previous: The MBRboot sectors +

+

Extended and logical partitions

+

+ The original partitioning scheme for PC hard disks allowed + only four partitions. This quickly turned out to be too little + in real life, partly because some people want more than four + operating systems (Linux, MS-DOS, OS/2, Minix, FreeBSD, NetBSD, or + Windows/NT, to name a few), but primarily because sometimes it + is a good idea to have several partitions for one + operating system. For example, swap space is usually best put + in its own partition for Linux instead of in the main + Linux partition for reasons of speed (see below). +

+ To overcome this design problem, extended partitions were + invented. This trick allows partitioning a primary + partition into sub-partitions. The + primary partition thus subdivided is the extended partition; the + subpartitions are logical partitions. They behave + like primarygif partitions, but are created + differently. There is no speed difference between them. +

+ The partition structure of a hard disk might look like that in + figure 4.2. The disk is divided into + three primary partitions, the second of which is divided into + two logical partitions. Part of the disk is not partitioned at + all. The disk as a whole and each primary partition has a boot + sector. +

+

  figure1122
+Figure 4.2: A sample hard disk partitioning.
+


+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node38.html b/sag-0.6.1-www/Invisible/sag-0.6/node38.html new file mode 100644 index 0000000..ff99643 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node38.html @@ -0,0 +1,45 @@ + + + + +Partition types + + + + + + + + next up previous contents index
+ Next: Partitioning a hard disk +Up: Partitions + Previous: Extended and logical partitions +

+

Partition types

+

+ The partition tables (the one in the MBR, and the ones for + extended partitions) contain one byte per partition that + identifies the type of that partition. This attempts to + identify the operating system that uses the partition, or what + it uses it for. The purpose is to make it possible to avoid + having two operating systems accidentally using the same + partition. However, in reality, operating systems do not + really care about the partition type byte; e.g., Linux + doesn't care at all what it is. Worse, some of them use it + incorrectly; e.g., at least some versions of DR-DOS ignore the + most significant bit of the byte, while others don't. +

+ There is no standardization agency to specify what each byte + value means, but some commonly accepted ones are included in + in table 4.1. The same list is + available in the Linux fdisk  program. +

+

  table1132
+Table 4.1: Partition types (from the Linux fdisk  program).
+


+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node39.html b/sag-0.6.1-www/Invisible/sag-0.6/node39.html new file mode 100644 index 0000000..e7433dd --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node39.html @@ -0,0 +1,84 @@ + + + + +Partitioning a hard disk + + + + + + + + next up previous contents index
+ Next: Device files and partitions +Up: Partitions + Previous: Partition types +

+

Partitioning a hard disk

+

+ There are many programs for creating and removing partitions. + Most operating systems have their own, and it can be a good + idea to use each operating system's own, just in case it does + something unusual that the others can't. Many of the programs + are called fdisk , including the Linux one, or + variations thereof. Details on using the Linux fdisk  + are given on its man page. The cfdisk  command is similar + to fdisk , but has a nicer (full screen) user interface. +

+ When using IDE disks, the boot partition (the partition + with the bootable kernel image files) must be completely + within the first 1024 cylinders. This is because the disk is + used via the BIOS during boot (before the system goes into + protected mode), and BIOS can't handle more than 1024 cylinders. + It is sometimes possible to use a boot partition that is only + partly within the first 1024 cylinders. This works as long + as all the files that are read with the BIOS are within the + first 1024 cylinders. Since this is difficult to arrange, + it is a very bad idea to do it; you never know when + a kernel update or disk defragmentation will result in an + unbootable system. Therefore, make sure your boot partition + is completely within the first 1024 cylinders. +

+ Some newer versions of the BIOS and IDE disks can, in fact, + handle disks with more than 1024 cylinders. If you have such + a system, you can forget about the problem; if you aren't + quite sure of it, put it within the first 1024 cylinders. +

+ Each partition should have an even number of sectors, since + the Linux filesystems use a 1 kB block size, i.e., two + sectors. An odd number of sectors will result in the last + sector being unused. This won't result in any problems, but + it is ugly, and some versions of fdisk  will warn about + it. +

+ Changing a partition's size usually requires first backing up + everything you want to save from that partition (preferably the + whole disk, just in case), deleting the partition, creating + new partition, then restoring everything to the new partition. + If the partition is growing, you may need to adjust the sizes + (and backup and restore) of the adjoining partitions as well. +

+ Since changing partition sizes is painful, it is preferable to + get the partitions right + the first time, or have an effective and easy to use backup + system. If you're installing from a media that does not require + much human intervention (say, from CD-ROM, as opposed to floppies), + it is often easy to play with different configuration at first. + Since you don't already have data to back up, it is not so + painful to modify partition sizes several times. +

+ There is a program for MS-DOS, called fips , which resizes + an MS-DOS partition without requiring the backup and restore, but + for other filesystems it is still necessary. +

+

next up previous contents index
+ Next: Device files and partitions +Up: Partitions + Previous: Partition types +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node4.html b/sag-0.6.1-www/Invisible/sag-0.6/node4.html new file mode 100644 index 0000000..37e434e --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node4.html @@ -0,0 +1,132 @@ + + + + +The Linux Documentation Project + + + + + + + + next up previous contents index
+ Next: Overview of a Linux +Up: Introduction + Previous: Typographical conventions +

+

The Linux Documentation Project

+

+The Linux Documentation Project, or LDP, is a loose team of writers, +proofreaders, and editors who are working together to provide complete +documentation for the Linux operating system. The overall +coordinator of the project is Greg Hankins. +

+This manual is one in a set of several being distributed by the LDP, +including a Linux Users' Guide, System Administrators' Guide, Network +Administrators' Guide, and Kernel Hackers' Guide. These manuals are +all available in LaTeX source format, .dvi format, and postscript +output by anonymous FTP from sunsite.unc.edu, in the directory +/pub/Linux/docs/LDP. +

+We encourage anyone with a penchant for writing or editing to join us in +improving Linux documentation. If you have Internet e-mail access, you can +contact Greg Hankins at gregh@sunsite.unc.edu. +

+ +

+

+The LDP Rhymegif
+

+

+ A wondrous thing,
+ and beautiful,
+ 'tis to write,
+ a book.
+

+

+ I'd like to sing,
+ of the sweat,
+ the blood and tear,
+ which it also took.
+

+

+ It started back in,
+ nineteen-ninety-two,
+ when users whined,
+ "we can nothing do!"
+

+

+ They wanted to know,
+ what their problem was,
+ and how to fix it
+ (by yesterday).
+

+

+ We put the answers in,
+ a Linux f-a-q,
+ hoped to get away,
+ from any more writin'.
+

+

+ "That's too long,
+ it's hard to search,
+ and we don't read it,
+ any-which-way!"
+

+

+ Then a few of us,
+ joined together
+ (virtually, you know),
+ to start the LDP.
+

+ +

+

+ We started to write,
+ or plan, at least,
+ several books,
+ one for every need.
+

+

+ The start was fun,
+ a lot of talk,
+ an outline,
+ then a slew.
+

+

+ Then silence came,
+ the work began,
+ some wrote less,
+ others more.
+

+

+ A blank screen,
+ oh its horrible,
+ it sits there,
+ laughs in the face.
+

+

+ We still await,
+ the final day,
+ when everything,
+ will be done.
+

+

+ Until then,
+ all we have,
+ is a draft,
+ for you to comment on. +

+ +

+

next up previous contents index
+ Next: Overview of a Linux +Up: Introduction + Previous: Typographical conventions +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node40.html b/sag-0.6.1-www/Invisible/sag-0.6/node40.html new file mode 100644 index 0000000..0e74e36 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node40.html @@ -0,0 +1,39 @@ + + + + +Device files and partitions + + + + + + + + next up previous contents index
+ Next: Filesystems +Up: Partitions + Previous: Partitioning a hard disk +

+

Device files and partitions

+

+ Each partition and extended partition has its own device file. + The naming convention for these files is that a partition's + number is appended after the name of the whole disk, with the + convention that 1-4 are primary partitions (regardless of + how many primary partitions there are) and 5-8 + are logical partitions (regardless of within which primary + partition they reside). For example, /dev/hda1  is the + first primary partition on the first IDE hard disk, and + /dev/sdb7  is the third extended partition on the second + SCSI hard disk. + The device list in [Anv] + gives more information. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node41.html b/sag-0.6.1-www/Invisible/sag-0.6/node41.html new file mode 100644 index 0000000..bfaecbf --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node41.html @@ -0,0 +1,41 @@ + + + + +Filesystems + + + + + + + + next up previous contents index
+ Next: What are filesystems? +Up: Using Disks and Other + Previous: Device files and partitions +

+

Filesystems

+

+  +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node42.html b/sag-0.6.1-www/Invisible/sag-0.6/node42.html new file mode 100644 index 0000000..3a78689 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node42.html @@ -0,0 +1,91 @@ + + + + +What are filesystems? + + + + + + + + next up previous contents index
+ Next: Filesystems galore +Up: Filesystems + Previous: Filesystems +

+

What are filesystems?

+

+ A filesystem is the methods and data structures that an + operating system uses to keep track of files on a disk or partition; + that is, the way the + files are organized on the disk. The word is also used to + refer to a partition or disk that is used to store the files + or the type of the filesystem. Thus, one might say ``I have + two filesystems'' meaning one has two partitions on which one + stores files, or that one is using the ``extended + filesystem'', meaning the type of the filesystem. +

+ The difference between a disk or partition and the filesystem + it contains is important. A few programs (including, + reasonably enough, programs that create filesystems) operate + directly on the raw sectors of a disk or partition; if there + is an existing file system there it will be destroyed or + seriously corrupted. Most programs operate on a filesystem, + and therefore won't work on a partition that doesn't contain + one (or that contains one of the wrong type). +

+ Before a partition or disk can be used as a filesystem, it + needs to be initialized, and the bookkeeping data structures need + to be written to the disk. This process is called + making a filesystem. +

+ Most UNIX filesystem types have a similar general structure, + although the exact details vary quite a bit. The central + concepts are superblock, inode, data block, + directory block, and indirection block. The + superblock contains information about the filesystem as a + whole, such as its size (the exact information here depends + on the filesystem). An inode contains all information about + a file, except its name. The name is stored in the directory, + together with the number of the inode. A directory entry consists + of a filename and the number of the inode which represents the + file. The inode contains the numbers of several data blocks, + which are used to store the data in the file. There is space + only for a few data block numbers in the inode, however, and if more + are needed, more space for pointers to the data blocks is allocated + dynamically. These dynamically allocated blocks are indirect + blocks; the name indicates that in order to find the data block, + one has to find its number in the indirect block first. +

+ UNIX filesystems usually allow one to create a hole + in a file (this is done with lseek ; check the manual + page), which means that the filesystem just pretends that at a + particular place in the file there is just zero bytes, but no + actual disk sectors are reserved for that place in the file + (this means that the file will use a bit less disk + space). This happens especially often for small binaries, Linux + shared libraries, some databases, and a few other special cases. + (Holes are + implemented by storing a special value as the address of the + data block in the indirect block or inode. This special address + means that no data block is allocated for that part of the file, + ergo, there is a hole in the file.) +

+ Holes are moderately useful. On the author's system, a simple + measurement showed a potential for about 4 MB of savings through + holes of about 200 MB total used disk space. That system, however, + contains relatively few programs and no database files. The + measurement tool is described in appendix A. +

+

next up previous contents index
+ Next: Filesystems galore +Up: Filesystems + Previous: Filesystems +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node43.html b/sag-0.6.1-www/Invisible/sag-0.6/node43.html new file mode 100644 index 0000000..d699677 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node43.html @@ -0,0 +1,146 @@ + + + + +Filesystems galore + + + + + + + + next up previous contents index
+ Next: Which filesystem should be +Up: Filesystems + Previous: What are filesystems? +

+

Filesystems galore

+

+ Linux supports several types of filesystems. As of this + writing the most important ones are: +

minix +
+ The oldest, presumed to be the most reliable, but quite + limited in features (some time stamps are missing, at + most 30 character filenames) and restricted in + capabilities (at most 64 MB per filesystem). +
xia +
+ A modified version of the minix filesystem that lifts + the limits on the filenames and filesystem sizes, + but does not otherwise introduce new features. It is + not very popular, but is reported to work very well. +
ext2 +
+ The most featureful of the native Linux filesystems, + currently also the most popular one. It is designed to + be easily upwards compatible, so that new versions + of the filesystem code do not require re-making the + existing filesystems. +
ext +
+ An older version of ext2 that wasn't upwards + compatible. It is hardly ever used in new installations + any more, and most people have converted to ext2. +

+

+ In addition, support for several foreign filesystem exists, + to make it easier to exchange files with other operating + systems. These foreign filesystems work just like native + ones, except that they may be lacking in some usual UNIX + features, or have curious limitations, or other oddities. +
msdos +
+ Compatibility with MS-DOS (and OS/2 and Windows NT) + FAT filesystems. +
umsdos +
+ Extends the msdos filesystem driver under + Linux to get long filenames, owners, + permissions, links, and device files. This allows a normal + msdos filesystem to be used as if it were a + Linux one, thus removing the need for a separate + partition for Linux. +
iso9660 +
+ The standard CD-ROM filesystem; the popular Rock Ridge + extension to the CD-ROM standard that allows longer file + names is supported automatically. +
nfs +
+ A networked filesystem that allows sharing a filesystem + between many computers to allow easy access to the + files from all of them. +
hpfs +
+ The OS/2 filesystem. +
sysv +
+ SystemV/386, Coherent, and Xenix filesystems. +

+

+ The choice of filesystem to use depends on the situation. If + compatibility or other reasons make one of the non-native + filesystems necessary, then that one must be used. If one can + choose freely, then it is probably wisest to use ext2, since + it has all the features but does not suffer from lack of + performance. +

+ There is also the proc filesystem, usually accessible as + the /proc  directory, which is not really a + filesystem at all, even though it looks like one. The + proc filesystem makes it easy to access certain kernel + data structures, such as the process list (hence the name). + It makes these + data structures look like a filesystem, and that filesystem + can be manipulated with all the usual file tools. For example, + to get a listing of all processes one might use the + command +

+$ ls -l /proc
+total 0
+dr-xr-xr-x 4 root root 0 Jan 31 20:37 1
+dr-xr-xr-x 4 liw users 0 Jan 31 20:37 63
+dr-xr-xr-x 4 liw users 0 Jan 31 20:37 94
+dr-xr-xr-x 4 liw users 0 Jan 31 20:37 95
+dr-xr-xr-x 4 root users 0 Jan 31 20:37 98
+dr-xr-xr-x 4 liw users 0 Jan 31 20:37 99
+-r--r--r-- 1 root root 0 Jan 31 20:37 devices
+-r--r--r-- 1 root root 0 Jan 31 20:37 dma
+-r--r--r-- 1 root root 0 Jan 31 20:37 filesystems
+-r--r--r-- 1 root root 0 Jan 31 20:37 interrupts
+-r-------- 1 root root 8654848 Jan 31 20:37 kcore
+-r--r--r-- 1 root root 0 Jan 31 11:50 kmsg
+-r--r--r-- 1 root root 0 Jan 31 20:37 ksyms
+-r--r--r-- 1 root root 0 Jan 31 11:51 loadavg
+-r--r--r-- 1 root root 0 Jan 31 20:37 meminfo
+-r--r--r-- 1 root root 0 Jan 31 20:37 modules
+dr-xr-xr-x 2 root root 0 Jan 31 20:37 net
+dr-xr-xr-x 4 root root 0 Jan 31 20:37 self
+-r--r--r-- 1 root root 0 Jan 31 20:37 stat
+-r--r--r-- 1 root root 0 Jan 31 20:37 uptime
+-r--r--r-- 1 root root 0 Jan 31 20:37 version
+$ +
+ (There will be a few extra files that don't correspond to + processes, though. The above example has been shortened.) +

+ Note that even though it is called a filesystem, no part of + the proc filesystem touches any disk. It exists only in the + kernel's imagination. Whenever anyone tries to look at any + part of the proc filesystem, the kernel makes it look as if + the part existed somewhere, even though it doesn't. So, even + though there is a multi-megabyte /proc/kcore  file, + it doesn't take any disk space. +

+

next up previous contents index
+ Next: Which filesystem should be +Up: Filesystems + Previous: What are filesystems? +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node44.html b/sag-0.6.1-www/Invisible/sag-0.6/node44.html new file mode 100644 index 0000000..1de8c1d --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node44.html @@ -0,0 +1,33 @@ + + + + +Which filesystem should be used? + + + + + + + + next up previous contents index
+ Next: Creating a filesystem +Up: Filesystems + Previous: Filesystems galore +

+

Which filesystem should be used?

+

+ There is usually little point in using many different filesystems. + Currently, ext2fs is the most popular one, and it is probably + the wisest choice. Depending on the overhead for bookkeeping + structures, speed, (perceived) reliability, compatibility, + and various other reasons, it may be advisable to use another file + system. This needs to be decided on a case-by-case basis. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node45.html b/sag-0.6.1-www/Invisible/sag-0.6/node45.html new file mode 100644 index 0000000..80a3f00 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node45.html @@ -0,0 +1,106 @@ + + + + +Creating a filesystem + + + + + + + + next up previous contents index
+ Next: Mounting and unmounting +Up: Filesystems + Previous: Which filesystem should be +

+

Creating a filesystem

+  +

+ Filesystems are created, i.e., initialized, with the mkfs  + command. There is actually a separate program for each filesystem + type. mkfs  is just a front end that runs the appropriate + program depending on the desired filesystem type. The type is + selected with the -t fstype option. +

+ The programs called by mkfs  have slightly different + command line interfaces. + The common and most important options are summarized below; see + the manual pages for more. +

-t fstype +
Select the type of the filesystem. +
-c +
Search for bad blocks and initialize the bad + block list accordingly. +
-l filename +
Read the initial bad block list + from the file filename. +

+

+ To create an ext2 filesystem on a floppy, one would give the + following commands: +
+$ fdformat -n /dev/fd0H1440
+Double-sided, 80 tracks, 18 sec/track. Total capacity 1440 kB.
+Formatting ... done
+$ badblocks /dev/fd0H1440 1440 > bad-blocks
+$ mkfs -t ext2 -l bad-blocks /dev/fd0H1440
+mke2fs 0.5a, 5-Apr-94 for EXT2 FS 0.5, 94/03/10
+360 inodes, 1440 blocks
+72 blocks (5.00%) reserved for the super user
+First data block=1
+Block size=1024 (log=0)
+Fragment size=1024 (log=0)
+1 block group
+8192 blocks per group, 8192 fragments per group
+360 inodes per group
+
+Writing inode tables: done
+Writing superblocks and filesystem accounting information: done
+$ +
+ First, the floppy was formatted (the -n option prevents + validation, i.e., bad block checking). Then bad blocks were + searched with badblocks , with the output redirected to + a file, bad-blocks. Finally, the filesystem was created, + with the bad block list initialized by whatever badblocks  + found. +

+ The -c option could have been used with mkfs  + instead of badblocks  and a separate file. The example + below does that. +

+$ mkfs -t ext2 -c /dev/fd0H1440
+mke2fs 0.5a, 5-Apr-94 for EXT2 FS 0.5, 94/03/10
+360 inodes, 1440 blocks
+72 blocks (5.00%) reserved for the super user
+First data block=1
+Block size=1024 (log=0)
+Fragment size=1024 (log=0)
+1 block group
+8192 blocks per group, 8192 fragments per group
+360 inodes per group
+
+Checking for bad blocks (read-only test): done
+Writing inode tables: done
+Writing superblocks and filesystem accounting information: done
+$ +
+ The -c is more convenient than a separate use of + badblocks , but badblocks  is necessary for checking + after the filesystem has been created. +

+ The process to prepare filesystems on hard disks or partitions + is the same as for floppies, except that the formatting isn't needed. +

+

next up previous contents index
+ Next: Mounting and unmounting +Up: Filesystems + Previous: Which filesystem should be +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node46.html b/sag-0.6.1-www/Invisible/sag-0.6/node46.html new file mode 100644 index 0000000..04e96e1 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node46.html @@ -0,0 +1,221 @@ + + + + +Mounting and unmounting + + + + + + + + next up previous contents index
+ Next: Checking filesystem integrity with +Up: Filesystems + Previous: Creating a filesystem +

+

Mounting and unmounting

+  +

+ Before one can use a filesystem, it has to be mounted. + The operating system then does various bookkeeping things to + make sure that everything works. Since all files in UNIX are + in a single directory tree, the mount operation will make it + look like the contents of the new filesystem are the contents of + an existing subdirectory in some already mounted filesystem. +

+ For example, figure 4.3 shows three + separate filesystems, each with their own root directory. + When the last two filesystems are mounted below /home  + and /usr , respectively, on the first filesystem, we + can get a single directory tree, as in + figure 4.4. +

+

  figure1226
+Figure 4.3: Three separate filesystems.
+

+

+

  figure1233
+Figure 4.4: /home  and /usr  have been mounted.
+

+

+ The mounts could be done as in the following example: +

+$ mount /dev/hda2 /home
+$ mount /dev/hda3 /usr
+$ +
+ The mount  command takes two arguments. The first one is + the device file corresponding to the disk or partition containing + the filesystem. The second one is the directory below which it + will be mounted. After these commands the contents of + the two filesystems look just like the contents of the /home  + and /usr  directories, respectively. One would then say that + ``/dev/hda2  is mounted on /home '', and similarly + for /usr . To look at either filesystem, one would look + at the contents of the directory on which it has been mounted, + just as if it were any other directory. Note the + difference between the device file, /dev/hda2 , and the + mounted-on directory, /home . The device file gives access + to the raw contents of the disk, the mounted-on directory + gives access to the files on the disk. The mounted-on directory + is called the mount point. +

+ Linux supports many filesystem types. mount  tries to + guess the type of the filesystem. You can also use the + -t fstype option to specify the type directly; + this is sometimes necessary, since the heuristics mount  + uses do not always work. For example, to mount an MS-DOS + floppy, you could use the following command: +

+$ mount -t msdos /dev/fd0 /floppy
+$ +
+ The mounted-on directory need not be empty, although it must + exist. Any files in it, + however, will be inaccessible by name while the filesystem + is mounted. (Any files that have already been opened will + still be accessible. Files that have hard links from + other directories can be accessed using those names.) + There is no harm done with this, and it can even be useful. + For instance, some people like to have /tmp  and /var/tmp  + synonymous, and make /tmp  be a symbolic link to /var/tmp . + When the system is booted, before the /usr  filesystem is + mounted, a /var/tmp  directory residing on the root filesystem + is used instead. When /usr  is mounted, it will make the + /var/tmp  directory on the root filesystem inaccessible. + If /var/tmp  didn't exist on the root filesystem, it would + be impossible to use temporary files before mounting /var . +

+ If you don't intend to write anything to the filesystem, use + the -r switch for mount  to do a readonly + mount. This will make the kernel stop any attempts at + writing to the filesystem, and will also stop the kernel from + updating file access times in the inodes. Read-only mounts + are necessary for unwritable media, e.g., CD-ROM's. +

+ The alert reader has already noticed a slight + logistical problem. How is the first filesystem (called the root + filesystem, because it contains the root directory) mounted, + since it obviously can't be mounted on another filesystem? + Well, the answer is that it is done by magic.gif The root filesystem is magically mounted at boot time, + and one can rely on it to always be mounted--if the root + filesystem can't be mounted, the system does not boot. The + name of the filesystem that is magically mounted as root is + either compiled into the kernel, or set using LILO or rdev . +

+ The root filesystem is usually first mounted readonly. The + startup scripts will then run fsck  to verify its + validity, and if there are no problems, they will re-mount + it so that writes will also be allowed. fsck  must not + be run on a mounted filesystem, since any changes to the + filesystem while fsck  is running will cause + trouble. Since the root filesystem + is mounted readonly while it is being checked, fsck  + can fix any problems without worry, since the remount operation + will flush any metadata that the filesystem keeps in memory. +

+ On many systems there are other filesystems that should also + be mounted automatically at boot time. These are specified + in the /etc/fstab  file; see the fstab  man page for + details on the + format. The details of exactly when the extra filesystems + are mounted depend on many factors, and can be configured + by each administrator if need be. When the chapter on booting + is finished, you may read all about it there. +

+ When a filesystem no longer needs to be mounted, it can be + unmounted with umount gif. umount  takes one argument: + either the device file or the mount point. + For example, to unmount the directories of + the previous example, one could use the commands +

+$ umount /dev/hda2
+$ umount /usr
+$ +
+ See the man page for further instructions on how to use the + command. It is imperative that you always unmount a mounted + floppy. Don't just pop the floppy out of the drive! + Because of disk caching, the data is not necessarily written + to the floppy until you unmount it, so removing the floppy + from the drive too early might cause the contents to become + garbled. If you only read from the floppy, this is not very + likely, but if you write, even accidentally, the result may be + catastrophic. +

+ Mounting and unmounting requires super user privileges, i.e., + only root  can do it. The reason for this is that if any + user can mount a floppy on any directory, then it is rather easy + to create a floppy with, say, a Trojan horse disguised as + /bin/sh , or any other often used program. However, it is + often necessary to allow users to use floppies, and there are + several ways to do this: +

+ The last alternative can be implemented by adding a line like + the following to the /etc/fstab  file: +
+/dev/fd0 /floppy msdos user,noauto 0 0 +
+ The columns are: device file to mount, directory to mount on, + filesystem type, options, backup frequency (used by dump ), + and fsck  pass number (to specify the order in which + filesystems should be checked upon boot; 0 means no check). +

+ The noauto option stops this mount to be done + automatically when the system is started (i.e., it stops + mount -a  from mounting it). The user option + allows any user to mount the filesystem, and, because of security + reasons, disallows execution of programs (normal or setuid) + and interpretation of device files from the mounted filesystem. + After this, any user can mount a floppy with an msdos + filesystem with the following command: +

+$ mount /floppy
+$ +
+ The floppy can (and needs to, of course) be unmounted with + the corresponding umount  command. +

+ If you want to provide access to several types of floppies, + you need to give several mount points. The settings can be + different for each mount point. For example, to give access + to both MS-DOS and ext2 floppies, you could have the following + to lines in /etc/fstab : +

+ 
/dev/fd0    /dosfloppy    msdos   user,noauto  0  0
+/dev/fd0    /ext2floppy   ext2    user,noauto  0  0
+
+ For MS-DOS filesystems (not just floppies), you probably want to + restrict access to it by using the uid, gid, + and umask  filesystem options, described in detail on the + mount  manual page. If you aren't careful, mounting + an MS-DOS filesystem gives everyone at least read access to the + files in it, which is not a good idea. +

+

next up previous contents index
+ Next: Checking filesystem integrity with +Up: Filesystems + Previous: Creating a filesystem +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node47.html b/sag-0.6.1-www/Invisible/sag-0.6/node47.html new file mode 100644 index 0000000..5fce368 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node47.html @@ -0,0 +1,86 @@ + + + + +Checking filesystem integrity with fsck + + + + + + + + next up previous contents index
+ Next: Checking for disk errors +Up: Filesystems + Previous: Mounting and unmounting +

+ 

Checking filesystem integrity with fsck

+

+ Filesystems are complex creatures, and as such, they tend to be + somewhat error-prone. A filesystem's correctness and validity + can be checked using the fsck  command. It can be + instructed to repair any minor problems it finds, and to + alert the user if there any unrepairable problems. Fortunately, + the code to implement filesystems is debugged quite + effectively, so there are seldom any problems at all, and they + are usually caused by power failures, failing hardware, or + operator errors; for example, by not shutting down the system + properly. +

+ Most systems are setup to run fsck  automatically at + boot time, so that any errors are detected (and hopefully + corrected) before the system is used. Use of a corrupted + filesystem tends to make things worse: if the data structures + are messed up, using the filesystem will probably mess them + up even more, resulting in more data loss. However, + fsck  can take a while to run on big filesystems, and + since errors almost never occur if the system has been shut + down properly, a couple of tricks are used to avoid doing the + checks in such cases. The first is that if the file /etc/fastboot  + exists, no checks are made. The second is that the ext2 filesystem + has a special marker in its superblock that tells whether + the filesystem was unmounted properly after the previous mount. + This allows e2fsck  (the version of fsck  for + the ext2 filesystem) to avoid checking the filesystem if + the flag indicates that the unmount was done (the assumption + being that a proper unmount indicates no problems). Whether + the /etc/fastboot  trick works on your system depends on + your startup scripts, but the ext2 trick works every time + you use e2fsck --it has to be explicitly bypassed with + an option to e2fsck  to be avoided. (See the e2fsck  + man page for details on how.) +

+ The automatic checking only works for the filesystems that are + mounted automatically at boot time. Use fsck  manually + to check other filesystems, e.g., floppies. +

+ If fsck  finds unrepairable problems, you need either + in-depth knowlege of how filesystems work in general, + and the type of the corrupt filesystem in particular, or + good backups. The latter is easy (although sometimes tedious) + to arrange, the former can sometimes be arranged via a friend, + the Linux newsgroups and mailing lists, + or some other source of support, if you don't have the + know-how yourself. I'd like to tell you more + about it, but my lack of education and experience in this regard + hinders me. The debugfs  program by Theodore T'so + should be useful. +

+ fsck  must only be run on unmounted filesystems, never on + mounted filesystems (with the exception of the read-only root + during startup). This is because it accesses the raw + disk, and can therefore modify the filesystem without the + operating system realizing it. There will be trouble, + if the operating system is confused. +

+

next up previous contents index
+ Next: Checking for disk errors +Up: Filesystems + Previous: Mounting and unmounting +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node48.html b/sag-0.6.1-www/Invisible/sag-0.6/node48.html new file mode 100644 index 0000000..bb507ee --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node48.html @@ -0,0 +1,52 @@ + + + + +Checking for disk errors with badblocks + + + + + + + + next up previous contents index
+ Next: Fighting fragmentation +Up: Filesystems + Previous: Checking filesystem integrity with +

+ 

Checking for disk errors with badblocks

+

+ It can be a good idea to periodically check for bad blocks. + This is done with the badblocks  command. It outputs + a list of the numbers of all bad blocks it can find. This list + can be fed to fsck  to be recorded + in the filesystem data structures so that the operating system + won't try to use the bad blocks for storing data. + The following example will show how this could be done. +

+$ badblocks /dev/fd0H1440 1440 > bad-blocks
+$ fsck -t ext2 -l bad-blocks /dev/fd0H1440
+Parallelizing fsck version 0.5a (5-Apr-94)
+e2fsck 0.5a, 5-Apr-94 for EXT2 FS 0.5, 94/03/10
+Pass 1: Checking inodes, blocks, and sizes
+Pass 2: Checking directory structure
+Pass 3: Checking directory connectivity
+Pass 4: Check reference counts.
+Pass 5: Checking group summary information.
+
+/dev/fd0H1440: ***** FILE SYSTEM WAS MODIFIED *****
+/dev/fd0H1440: 11/360 files, 63/1440 blocks
+$ +
+ If badblocks reports a block that was already used, e2fsck  + will try to move the block to another place. If the block was really + bad, not just marginal, the contents of the file may be corrupted. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node49.html b/sag-0.6.1-www/Invisible/sag-0.6/node49.html new file mode 100644 index 0000000..190bc21 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node49.html @@ -0,0 +1,50 @@ + + + + +Fighting fragmentation + + + + + + + + next up previous contents index
+ Next: Other tools for all +Up: Filesystems + Previous: Checking for disk errors +

+

Fighting fragmentation

+

+ When a file is written to disk, it can't always be written + in consecutive blocks. A file that is not stored in + consecutive blocks is fragmented. It takes longer + to read a fragmented file, since the disk's read-write head + will have to move more. It is desireable to avoid fragmentation, + although it is less of a problem in a system with a good buffer + cache with read-ahead. +

+ The ext2 filesystem attempts to keep fragmentation at a minimum, + by keeping all blocks in a file close together, even if they + can't be stored in consecutive sectors. Ext2 effectively always + allocates the free block that is nearest to other blocks in a file. + For ext2, it is therefore seldom necessary to worry about + fragmentation. There is a program for defragmenting an ext2 + filesystem, see [TV] in the bibliography. +

+ There are many MS-DOS defragmentation programs that move blocks + around in the filesystem to remove fragmentation. For other + filesystems, defragmentation must be done by backing up the + filesystem, re-creating it, and restoring the files from backups. + Backing up a filesystem before defragmening is a good idea + for all filesystems, since many things can go wrong during + the defragmentation. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node5.html b/sag-0.6.1-www/Invisible/sag-0.6/node5.html new file mode 100644 index 0000000..c433b5a --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node5.html @@ -0,0 +1,61 @@ + + + + +Overview of a Linux System + + + + + + + + next up previous contents index
+ Next: Various parts of an +Up: Linux System Administrators' Guide + Previous: The Linux Documentation Project +

+

Overview of a Linux System

+

+  +

+

+ + God looked over everything he had made,
+ and saw that it was very good.
+ Genesis 1:31
+

+

+ This chapter gives an overview of a Linux system. First, the major + services provided by the operating system are described. Then, + the programs that implement these services are described with a + considerable lack of detail. The + purpose of this chapter is to give an understanding of the + system as a whole, so that each part is described in detail elsewhere. +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node50.html b/sag-0.6.1-www/Invisible/sag-0.6/node50.html new file mode 100644 index 0000000..2a4b7f6 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node50.html @@ -0,0 +1,40 @@ + + + + +Other tools for all filesystems + + + + + + + + next up previous contents index
+ Next: Other tools for the +Up: Filesystems + Previous: Fighting fragmentation +

+

Other tools for all filesystems

+

+ Some other tools are also useful for managing filesystems. + df  shows the free disk space on one or more filesystems; + du  shows how much disk space a directory and all its + files contain. These can be used to hunt down disk space + wasters. +

+ sync  forces all unwritten blocks in the buffer cache + (see section 5.6) to be written to disk. + It is seldom necessary to do this by hand; the daemon process + update  does this automatically. It can be useful in + catastrophies, for example if update  or its helper process + bdflush  dies, or if you must turn off power now  and + can't wait for update  to run. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node51.html b/sag-0.6.1-www/Invisible/sag-0.6/node51.html new file mode 100644 index 0000000..e09dc53 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node51.html @@ -0,0 +1,80 @@ + + + + +Other tools for the ext2 filesystem + + + + + + + + next up previous contents index
+ Next: Disks without filesystems +Up: Filesystems + Previous: Other tools for all +

+

Other tools for the ext2 filesystem

+

+ In addition to the filesystem creator (mke2fs ) and + checker (e2fsck ) accessible directly or via the + filesystem type independent front ends, the ext2 + filesystem has some additional tools that can be useful. +

+ tune2fs  adjusts filesystem parameters. Some of the + more interesting parameters are: +

+ See the tune2fs  manual page for more information. +

+ dumpe2fs  shows information about an ext2 filesystem, mostly + from the superblock. Figure 4.5 shows + a sample output. Some of the information in the output is + technical and requires understanding of how the filesystem + works (see appendix gif), but much of + it is readily understandable even for layadmins. +

+

  figure1374
+Figure 4.5: Sample output from dumpe2fs 
+

+

+ debugfs  is a filesystem debugger. It allows direct + access to the filesystem data structures stored on disk and + can thus be used to repair a disk that is so broken that + fsck  can't fix it automatically. It has also been known + to be used to recover deleted files. However, debugfs  + very much requires that you understand what you're doing; + a failure to understand can destroy all your data. +

+ dump  and restore  can be used to back up an + ext2 filesystem. They are ext2 specific versions of the + traditional UNIX backup tools. See chapter 10 + for more information on backups. +

+

next up previous contents index
+ Next: Disks without filesystems +Up: Filesystems + Previous: Other tools for all +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node52.html b/sag-0.6.1-www/Invisible/sag-0.6/node52.html new file mode 100644 index 0000000..2938b1b --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node52.html @@ -0,0 +1,61 @@ + + + + +Disks without filesystems + + + + + + + + next up previous contents index
+ Next: Allocating disk space +Up: Using Disks and Other + Previous: Other tools for the +

+

Disks without filesystems

+

+ Not all disks or partitions are used as filesystems. A swap + partition, for example, will not have a filesystem on it. Many + floppies are used in a tape-drive emulating fashion, so that + a tar  or other file is written directly on the raw disk, + without a filesystem. Linux boot floppies don't contain a + filesystem, only the raw kernel. +

+ Avoiding a filesystem has the advantage of making more of the + disk usable, since a filesystem always has some bookkeeping + overhead. It also makes the disks more easily compatible with + other systems: for example, the tar  file format is the same + on all systems, while filesystems are different on most systems. + You will quickly get used to disks without filesystems if you + need them. Bootable Linux floppies also do not necessarily have + a filesystem, although that is also possible. +

+ One reason to use raw disks is to make image copies of them. + For instance, if the disk contains a partially damaged filesystem, + it is a good idea to make an exact copy of it before trying to + fix it, since then you can start again if your fixing breaks things + even more. One way to do this is to use dd : +

+$ dd if=/dev/fd0H1440 of=floppy-image
+2880+0 records in
+2880+0 records out
+$ dd if=floppy-image of=/dev/fd0H1440
+2880+0 records in
+2880+0 records out
+$ +
+ The first dd  makes an exact image of the floppy to the file + floppy-image , the second one writes the image to the floppy. + (The user has presumably switched the floppy before the second + command. Otherwise the command pair is of doubtful usefulness.) +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node53.html b/sag-0.6.1-www/Invisible/sag-0.6/node53.html new file mode 100644 index 0000000..0897794 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node53.html @@ -0,0 +1,34 @@ + + + + +Allocating disk space + + + + + + + + next up previous contents index
+ Next: Partitioning schemes +Up: Using Disks and Other + Previous: Disks without filesystems +

+

Allocating disk space

+

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node54.html b/sag-0.6.1-www/Invisible/sag-0.6/node54.html new file mode 100644 index 0000000..b4fa706 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node54.html @@ -0,0 +1,78 @@ + + + + +Partitioning schemes + + + + + + + + next up previous contents index
+ Next: Space requirements +Up: Allocating disk space + Previous: Allocating disk space +

+

Partitioning schemes

+

+ It is not easy to partition a disk in the best possible way. + Worse, there is no universally correct way to + do it; there are too many factors involved. +

+ The traditional way is to have a (relatively) small root + filesystem, which contains /bin , /etc , /dev , + /lib , /tmp , and other stuff that is needed to get the + system up and running. This way, the root filesystem (in its + own partition or on its own disk) is all that is needed to bring + up the system. The reasoning is that if the root filesystem is + small and is not heavily used, it is less likely to become + corrupt when the system crashes, and you will therefore find it + easier to fix any problems caused by the crash. Then you create + separate partitions or use separate disks for the directory tree + below /usr , the users' home directories (often under + /home ), and the swap space. Separating the home + directories (with the users' files) in their own partition makes + backups easier, since it is usually not necessary to backup + programs (which reside below /usr ). In a networked + environment it is also possible to share /usr  among several + machines (e.g., by using NFS), thereby reducing the total disk + space required by several tens or hundreds of megabytes times + the number of machines. +

+ The problem with having many partitions is that it splits the + total amount of free disk space into many small pieces. + Nowadays, when disks and (hopefully) operating systems are + more reliable, many people prefer to have just one partition + that holds all their files. On the other hand, it can be less + painful to back up (and restore) a small partition. +

+ For a small hard disk (assuming you don't do kernel + development), the best way to go is probably to have just one + partition. For large hard disks, it is probably + better to have a few large partitions, just in case + something does go wrong. (Note that `small' and `large' are + used in a relative sense here; your needs for disk space + decide what the threshold is.) +

+ If you have several disks, you might wish to have the root + filesystem (including /usr ) on one, and the users' home + directories on another. +

+ It is a good idea to be prepared to experiment a bit with + different partitioning schemes (over time, not just while + first installing the system). This is a bit of work, since it + essentially requires you to install the system from scratch + several times, but it is the only way to be sure you do it right. +

+

next up previous contents index
+ Next: Space requirements +Up: Allocating disk space + Previous: Allocating disk space +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node55.html b/sag-0.6.1-www/Invisible/sag-0.6/node55.html new file mode 100644 index 0000000..ed58c1c --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node55.html @@ -0,0 +1,51 @@ + + + + +Space requirements + + + + + + + + next up previous contents index
+ Next: Examples of hard disk +Up: Allocating disk space + Previous: Partitioning schemes +

+

Space requirements

+

+ The Linux distribution you install will give some indication + of how much disk space you need for various configurations. + Programs installed separately may also do the same. This will + help you plan your disk space usage, but you should prepare + for the future and reserve some extra space for things you will + notice later that you need. +

+ The amount you need for user files depends on what your users + wish to do. Most people seem to need as much space for their + files as possible, but the amount they will live happily with + varies a lot. Some people do only light text processing and + will survive nicely with a few megabytes, others do heavy + image processing and will need gigabytes. +

+ By the way, when comparing file sizes given in kilobytes or + megabytes and + disk space given in megabytes, it can be important to know that + the two units can be different. Some disk manufacturers like + to pretend that a kilobyte is 1000 bytes and a megabyte is + 1000 kilobytes, while all the rest of the computing world + uses 1024 for both factors. Therefore, my 345 MB hard disk + is really a 330 MB hard disk.gif +

+ Swap space allocation is discusses in section 5.5. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node56.html b/sag-0.6.1-www/Invisible/sag-0.6/node56.html new file mode 100644 index 0000000..6628aeb --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node56.html @@ -0,0 +1,56 @@ + + + + +Examples of hard disk allocation + + + + + + + + next up previous contents index
+ Next: Adding more disk space +Up: Allocating disk space + Previous: Space requirements +

+

Examples of hard disk allocation

+

+ I used to have a 109 MB hard disk. Now I am using a 330 MB + hard disk. I'll explain how and why I partitioned these + disks. +

+ The 109 MB disk I partitioned in a lot of ways, when my needs + and the operating systems I used changed; I'll explain two + typical scenarios. First, I used to run MS-DOS + together with Linux. For that, I needed about 20 MB of + hard disk, or just enough to have MS-DOS, a C compiler, an + editor, a few other utilities, the program I was working on, + and enough free disk space to not feel claustrophobic. For + Linux, I had a 10 MB swap partition, and the rest, or 79 MB, + was a single partition with all the files I had under + Linux. I experimented with having separate root, + /usr , and /home  partitions, but there was never + enough free disk space in one piece to do much interesting. +

+ When I didn't need MS-DOS anymore, I repartitioned the disk so + that I had a 12 MB swap partition, and again had the rest as a + single filesystem. +

+ The 330 MB disk is partitioned into several partitions, like + this: +


tabular1415
+ The scratch partition is for playing around with things that + require their own partition, e.g., trying different Linux + distributions, or comparing speeds of filesystems. When not + needed for anything else, it is used as swap space (I like to + have a lot of open windows). +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node57.html b/sag-0.6.1-www/Invisible/sag-0.6/node57.html new file mode 100644 index 0000000..5a56c52 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node57.html @@ -0,0 +1,33 @@ + + + + +Adding more disk space for Linux + + + + + + + + next up previous contents index
+ Next: Tips for saving disk +Up: Allocating disk space + Previous: Examples of hard disk +

+

Adding more disk space for Linux

+

+ Adding more disk space for Linux is easy, at least after the + hardware has been properly installed (the hardware installation is + outside the scope of this book). You format it if necessary, + then create the partitions and filesystem as described above, and + add the proper lines to /etc/fstab  so that it is mounted + automatically. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node58.html b/sag-0.6.1-www/Invisible/sag-0.6/node58.html new file mode 100644 index 0000000..79fd470 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node58.html @@ -0,0 +1,48 @@ + + + + +Tips for saving disk space + + + + + + + + next up previous contents index
+ Next: Memory Management +Up: Allocating disk space + Previous: Adding more disk space +

+

Tips for saving disk space

+

+ The best tip for saving disk space is to avoid installing + unnecessary programs. Most Linux distributions have an + option to install only part of the packages they contain, + and by analyzing your needs you might notice that you don't + need most of them. This will help save a lot of disk space, + since many programs are quite large. Even if you do need a + particular package or program, you might not need all of it. + For example, some on-line documentation might be unnecessary, + as might some of the Elisp files for GNU Emacs, some of the + fonts for X11, or some of the libraries for programming. +

+ If you cannot uninstall packages, you might look into + compression. Compression programs such as gzip  or + zip  will compress (and uncompress) individual files + or groups of files. The gzexe  system will compress and + uncompress programs invisibly to the user (unused programs + are compressed, then uncompressed as they are used). + The experimental DouBle  system + will compress all files in a filesystem, invisibly to the + programs that use them. (If you are familiar with products + such as Stacker for MS-DOS, the principle is the same.) +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node59.html b/sag-0.6.1-www/Invisible/sag-0.6/node59.html new file mode 100644 index 0000000..05d956f --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node59.html @@ -0,0 +1,49 @@ + + + + +Memory Management + + + + + + + + next up previous contents index
+ Next: What is virtual memory? +Up: Linux System Administrators' Guide + Previous: Tips for saving disk +

+

Memory Management

+   +

+

+ + Minnet, jag har tappat mitt minne,
+ är jag svensk eller finne
+ kommer inte ihåg...
+ (Bosse Österberg)
+

+

+ This section describes the Linux memory management features, + i.e., virtual memory and the disk buffer cache. The purpose and + workings and the things the system administrator needs to take + into consideration are described. +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node6.html b/sag-0.6.1-www/Invisible/sag-0.6/node6.html new file mode 100644 index 0000000..2255946 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node6.html @@ -0,0 +1,78 @@ + + + + +Various parts of an operating system + + + + + + + + next up previous contents index
+ Next: Important parts of the +Up: Overview of a Linux + Previous: Overview of a Linux +

+

Various parts of an operating system

+

+ A UNIX operating system consists of a kernel and some + system programs. There are also some application + programs for doing work. The kernel is the heart of the operating + systemgif. It keeps track + of files on the disk, starts programs and runs them + concurrently, assigns + memory and other resources to various processes, receives packets + from and sends packets to the network, and so on. The kernel does + very little by itself, but it provides tools with which all + services can be built. It also prevents anyone from accessing + the hardware directly, forcing everyone to use the tools it provides. + This way the kernel provides + some protection for users from each other. The tools provided + by the kernel are used via system calls; see manual page + section 2 for more information on these. +  +  +  +  +  +

+ The system programs use the tools provided by the kernel to + implement the various services required from an operating system. + System programs, and all other programs, run `on top of the kernel', + in what is called the user mode. + The difference between system and application programs is one + of intent: applications are intended for getting useful things + done (or for playing, if it happens to be a game), whereas + system programs are needed to get the system working. A word + processor is an application; telnet  is a system program. + The difference is often somewhat blurry, however, and is important + only to compulsive categorizers. +  +

+ An operating system + can also contain compilers and their corresponding libraries (GCC and + the C library in particular under Linux), although not all + programming languages need be part of the operating system. + Documentation, and sometimes even games, can also be part of it. + Traditionally, the operating system has been defined by the + contents of the installation tape or disks; with Linux it is + not as clear since it is spread all over the + FTP sites of the world. +  +  +  +  +  +

+

next up previous contents index
+ Next: Important parts of the +Up: Overview of a Linux + Previous: Overview of a Linux +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node60.html b/sag-0.6.1-www/Invisible/sag-0.6/node60.html new file mode 100644 index 0000000..39ad118 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node60.html @@ -0,0 +1,69 @@ + + + + +What is virtual memory? + + + + + + + + next up previous contents index
+ Next: Creating a swap space +Up: Memory Management + Previous: Memory Management +

+

What is virtual memory?

+

+ Linux supports virtual memory, that is, using a + disk as an extension of RAM so that the effective size of + usable memory grows correspondingly. The kernel will write + the contents of a currently unused block of memory to the + hard disk so that the memory can be used for another purpose. + When the original contents are needed again, they are read + back into memory. This is + all made completely transparent to the user; programs running under + Linux only see the larger amount of memory available and + don't notice that parts of them reside on the disk from + time to time. Of course, reading and writing the hard disk is + slower (on the order of a thousand times slower) than using + real memory, so the programs don't run as fast. The part of + the hard disk that is used as virtual memory + is called the swap space. +

+ Linux can use either a normal file in the filesystem or a + separate partition for swap space. A swap partition is + faster, but it is easier to change the size of a swap file + (there's no need to repartition the whole hard disk, and + possibly install everything from scratch). When you know how + much swap space you need, you should go for a swap partition, + but if you are uncertain, you can use a swap file first, use + the system for a while so that you can get a feel for how much + swap you need, and then make a swap partition when you're + confident about its size. +

+ You should also know that Linux allows one to use several swap + partitions and/or swap files at the same time. This means + that if you only occasionally need an unusual amount of swap space, + you can set up an extra swap file at such times, instead of + keeping the whole amount allocated all the time. +

+ A note on operating system terminology: computer science usually + distinguishes between swapping (writing the whole process out to + swap space) and paging (writing only fixed size parts, usually + a few kilobytes, at a time). Paging is usually more efficient, + and that's what Linux does, but traditional Linux terminology + talks about swapping anyway.gif +

+

next up previous contents index
+ Next: Creating a swap space +Up: Memory Management + Previous: Memory Management +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node61.html b/sag-0.6.1-www/Invisible/sag-0.6/node61.html new file mode 100644 index 0000000..5385417 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node61.html @@ -0,0 +1,93 @@ + + + + +Creating a swap space + + + + + + + + next up previous contents index
+ Next: Using a swap space +Up: Memory Management + Previous: What is virtual memory? +

+

Creating a swap space

+

+ A swap file is an ordinary file; it is in no way special to + the kernel. The only thing that matters to the kernel is that + it has no holes, and that it is prepared for use with + mkswap . It must reside on a local disk, however; it + can't reside in a filesystem that has been mounted over NFS + due to implementation reasons. +

+ The bit about holes is important. The swap file + reserves the disk space so that the kernel can quickly swap out + a page without having to go through all the things + that are necessary when allocating a disk sector to a file. + The kernel merely uses any sectors that have already been + allocated to the file. Because a hole in a file means that + there are no disk sectors allocated (for that place in the + file), it is not good for the kernel to try to use them. +

+ One good way to create the swap file without holes is through + the following command: +

+$ dd if=/dev/zero of=/extra-swap bs=1024 count=1024
+1024+0 records in
+1024+0 records out
+$ +
+ where /extra-swap  is the name of the swap file and + the size of is given after the count=. It is best for + the size to be a multiple of 4, because the kernel writes out + memory pages, which are 4 kilobytes in size. If the + size is not a multiple of 4, the last couple of kilobytes may + be unused. +

+ A swap partition is also not special in any way. You create it + just like any other partition; the only difference is that it is + used as a raw partition, that is, it will not contain any + filesystem at all. It is a good idea to mark swap partitions as + type 82 (Linux swap); this will the make partition listings + clearer, even though it is not strictly necessary to the kernel. +

+ After you have created a swap file or a swap partition, you + need to write a signature to its beginning; this contains some + administrative information and is used by the kernel. The + command to do this is mkswap , used like this: +

+$ mkswap /extra-swap 1024
+Setting up swapspace, size = 1044480 bytes
+$ +
+ Note that the swap space is still not in use yet: it + exists, but the kernel does not use it to provide virtual + memory. +

+ You should be very careful when using mkswap , since it + does not check that the file or partition isn't used for anything + else. You can easily overwrite important files and + partitions with mkswap ! Fortunately, you should only + need to use mkswap  when you install your system. +

+ The Linux memory manager limits the size of each swap space to + about 127 MB (for various technical reasons, the actual limit + is tex2html_wrap_inline4269 bytes, or + 127.6875 megabytes). You can, however, use up to + 16 swap spaces simultaneously, for a total of almost + 2 GB.gif +

+

next up previous contents index
+ Next: Using a swap space +Up: Memory Management + Previous: What is virtual memory? +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node62.html b/sag-0.6.1-www/Invisible/sag-0.6/node62.html new file mode 100644 index 0000000..3cf8f07 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node62.html @@ -0,0 +1,104 @@ + + + + +Using a swap space + + + + + + + + next up previous contents index
+ Next: Sharing swap spaces with +Up: Memory Management + Previous: Creating a swap space +

+

Using a swap space

+

+ An initialized swap space is taken into use with swapon . + This command tells the kernel that the swap + space can be used. The path to the swap space is given as + the argument, so to start swapping on a temporary swap + file one might use the following command. +

+$ swapon /extra-swap
+$ +
+ Swap spaces can be used automatically by listing them in + the /etc/fstab  file. +
+/dev/hda8 none swap sw 0 0
+/swapfile none swap sw 0 0 +
+ The startup scripts will run + the command swapon -a, which will start swapping on + all the swap spaces listed in /etc/fstab . Therefore, + the swapon  command is usually used only when extra swap + is needed. +

+ You can monitor the use of swap spaces with free . + It will tell the total amount of swap space used. +

+$ free
+ total used free shared buffers
+Mem: 15152 14896 256 12404 2528
+-/+ buffers: 12368 2784
+Swap: 32452 6684 25768
+$ +
+ The first line of output (Mem:) shows the physical memory. + The total column does not show the physical memory used by the + kernel, which is usually about a megabyte. The used column shows + the amount of memory used (the second line does not count buffers). + The free column shows completely unused memory. The shared column shows + the amount of memory shared by several processes; the more, the merrier. + The buffers column shows the current size of the disk buffer cache. +

+ That last line (Swap:) shows similar information for the swap + spaces. If this line is all zeroes, your swap space is not activated. +

+ The same information is available via top , + or using the proc filesystem in file /proc/meminfo . + It is + currently difficult to get information on the use of a specific + swap space. +

+ A swap space can be removed from use with swapoff . + It is usually not necessary to do it, except for temporary + swap spaces. + Any pages in use in the swap space are swapped in first; if + there is not sufficient physical memory to hold them, they will + then be swapped out (to some other swap space). + If there is not enough virtual memory to hold all of the pages + Linux will start to thrash; after a long while it should + recover, but meanwhile the system is unusable. You should + check (e.g., with free ) that there is enough free + memory before removing a swap space from use. +

+ All the swap spaces that are used automatically with + swapon -a can be removed from use with swapoff -a; + it looks at the file /etc/fstab  to find what to remove. + Any manually used swap spaces will remain in use. +

+ Sometimes a lot of swap space can be in use even though there + is a lot of free physical memory. This can happen for instance + if at one point there is need to swap, but later a big process + that occupied much of the physical memory terminates and + frees the memory. The swapped-out data is not + automatically swapped in until it is needed, so the physical + memory may remain free for a long time. There is no need to + worry about this, but it can be comforting to know what is + happening. +

+

next up previous contents index
+ Next: Sharing swap spaces with +Up: Memory Management + Previous: Creating a swap space +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node63.html b/sag-0.6.1-www/Invisible/sag-0.6/node63.html new file mode 100644 index 0000000..d78f823 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node63.html @@ -0,0 +1,33 @@ + + + + +Sharing swap spaces with other operating systems + + + + + + + + next up previous contents index
+ Next: Allocating swap space +Up: Memory Management + Previous: Using a swap space +

+

Sharing swap spaces with other operating systems

+

+ Virtual memory is built into many operating systems. Since they + each need it only when they are running, i.e., never at the same + time, the swap spaces of all but the currently running one are being + wasted. It would be more efficient for them to share a single + swap space. This is possible, but can require a bit of hacking. + The Tips-HOWTO contains some advice on how to implement this. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node64.html b/sag-0.6.1-www/Invisible/sag-0.6/node64.html new file mode 100644 index 0000000..e5bf5af --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node64.html @@ -0,0 +1,111 @@ + + + + +Allocating swap space + + + + + + + + next up previous contents index
+ Next: The buffer cache +Up: Memory Management + Previous: Sharing swap spaces with +

+

Allocating swap space

+   +

+ Some people will tell you that you should allocate twice as much + swap space as you have physical memory, but this is a bogus rule. + Here's how to do it properly: +

+

    +
  1. +

    + Estimate your total memory needs. This is the largest amount of + memory you'll probably need at a time, that is the sum of the + memory requirements of all the programs you want to run at the + same time. This can be done by running at the same time all the + programs you are likely to ever be running at the same time. +

    + For instance, if you want to run X, you should allocate + about 8 MB for it, gcc wants several megabytes (some + files need an unusually large amount, up to tens of + megabytes, but usually about four should do), and so on. + The kernel will use about a megabyte by itself, and the + usual shells and other small utilities perhaps a few + hundred kilobytes (say a megabyte together). There is + no need to try to be exact, rough estimates are fine, + but you might want to be on the pessimistic side. +

    + Remember that if there are going to be several people + using the system at the same time, they are all going + to consume memory. However, if two people run the same + program at the same time, the total memory consumption + is usually not double, since code pages and shared + libraries exist only once. +

    + The free  and ps  commands are useful for + estimating the memory needs. +

  2. +

    + Add some security to the estimate in step 1. This is because + estimates of program sizes will probably be wrong, because + you'll probably forget some programs you want to run, and to + make certain that you have some extra space just in case. A + couple of megabytes should be fine. (It is better to allocate + too much than too little swap space, but there's no need to + over-do it and allocate the whole disk, since unused swap space + is wasted space; see later about adding more swap.) Also, + since it is nicer to deal with even numbers, you can round the + value up to the next full megabyte. +

  3. +

    + Based on the computations above, you know how much memory + you'll be needing in total. So, in order to allocate + swap space, you just need to subtract the size of your + physical memory from the total memory needed, and you + know how much swap space you need. (On some versions + of UNIX, you need to allocate space for an image of the + physical memory as well, so the amount computed in step + 2 is what you need and you shouldn't do the subtraction.) +

  4. +

    + If your calculated swap space is very much larger than your + physical memory (more than a couple times larger), you should + probably invest in more physical memory, otherwise performance + will be too low. +

    +

+

+ It's a good idea to have at least some swap space, even if + your calculations indicate that you need none. Linux uses + swap space somewhat aggressively, so that as much physical + memory as possible can be kept free. Linux will swap out + memory pages that have not been used, even if the memory + is not yet needed for anything. This avoids waiting for + swapping when it is needed--the swapping can be done + earlier, when the disk is otherwise idle. +

+ Swap space can be divided among several disks. This + can sometimes improve performance, depending on the + relative speeds of the disks and the access patterns + of the disks. You might want to experiment with a few + schemes, but be aware that doing the experiments + properly is quite difficult. You should not believe + claims that any one scheme is superior to any other, + since it won't always be true. +

+

next up previous contents index
+ Next: The buffer cache +Up: Memory Management + Previous: Sharing swap spaces with +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node65.html b/sag-0.6.1-www/Invisible/sag-0.6/node65.html new file mode 100644 index 0000000..15f0462 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node65.html @@ -0,0 +1,125 @@ + + + + +The buffer cache + + + + + + + + next up previous contents index
+ Next: Boots And Shutdowns +Up: Memory Management + Previous: Allocating swap space +

+

The buffer cache

+

+  +

+ Reading from a diskgif is very slow compared to accessing (real) memory. + In addition, it is common to read the same part of a disk + several times during relatively short periods of time. For + example, one might first read an e-mail message, then read the + letter into an editor when replying to it, then make the mail + program read it again when copying it to a folder. Or, + consider how often the command ls  might be run on a + system with many users. By reading the information from disk + only once and then keeping it in memory until no longer + needed, one can speed up all but the first read. This is + called disk buffering, and the memory used for the + purpose is called the buffer cache. +

+ Since memory is, unfortunately, a finite, nay, scarce resource, + the buffer + cache usually cannot be big enough (it can't hold all the data one + ever wants to use). When the cache fills up, the data that + has been unused for the longest time is discarded and the + memory thus freed is used for the new data. +

+ Disk buffering works for writes as well. On the one hand, + data that is written is often soon read again (e.g., a source + code file is saved to a file, then read by the compiler), so + putting data that is written in the cache is a good idea. On + the other hand, by only putting the data into the cache, not + writing it to disk at once, the program that writes runs + quicker. The writes can then be done in the background, + without slowing down the other programs. +

+ Most operating systems have buffer caches (although + they might be called something else), but not all + of them work according to the above principles. + Some are write-through: the data is written + to disk at once (it is kept in the cache as well, + of course). The cache is called write-back + if the writes are done at a later time. Write-back is + more efficient than write-through, but also a bit more + prone to errors: if the machine crashes, or the power + is cut at a bad moment, or the floppy is removed from + the disk drive before the data in the cache waiting to + be written gets written, the changes in the cache are + usually lost. This might even mean that the filesystem + (if there is one) is not in full working order, perhaps + because the unwritten data held important changes to + the bookkeeping information. +

+ Because of this, you should never turn off the + power without using a proper shutdown procedure (see chapter + 6), or remove a floppy from the disk + drive until it has been unmounted (if it was mounted) + or after whatever program is using it has signaled + that it is finished and the floppy drive light doesn't + shine anymore. The sync  command flushes + the buffer, i.e., forces all unwritten data to be + written to disk, and can be used when one wants to be + sure that everything is safely written. In traditional + UNIX systems, there is a program called update  + running in the background which does a sync  + every 30 seconds, so it is usually not necessary + to use sync . Linux has an additional daemon, + bdflush , which does a more imperfect sync more + frequently to avoid the sudden freeze due to heavy disk + I/O that sync  sometimes causes. +

+ Under Linux, bdflush  is started by update . There is + usually no reason to worry about it, but if bdflush  happens + to die for some reason, the kernel will warn about this, and you + should start it by hand (/sbin/update ). +

+ The cache does not actually buffer files, but blocks, which are + the smallest units of disk I/O (under Linux, they are usually + 1 kB). This way, also directories, super blocks, other + filesystem bookkeeping data, and non-filesystem disks are + cached. +

+ The effectiveness of a cache is primarily decided by its size. + A small cache is next to useless: it will hold so little data + that all cached data is flushed from the cache before it + is reused. The critical size depends on how much data is read + and written, and how often the same data is accessed. The + only way to know is to experiment. +

+ If the cache is of a fixed size, it is not very good to have + it too big, either, because that might make the free memory + too small and cause swapping (which is also slow). To make + the most efficient use of real memory, Linux automatically + uses all free RAM for buffer cache, but also automatically + makes the cache smaller when programs need more memory. +

+ Under Linux, you do not need to do anything to make use of + the cache, it happens completely automatically. Except for + following the proper procedures for shutdown and removing + floppies, you do not need to worry about it. +

+

next up previous contents index
+ Next: Boots And Shutdowns +Up: Memory Management + Previous: Allocating swap space +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node66.html b/sag-0.6.1-www/Invisible/sag-0.6/node66.html new file mode 100644 index 0000000..9e6a9ff --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node66.html @@ -0,0 +1,56 @@ + + + + +Boots And Shutdowns + + + + + + + + next up previous contents index
+ Next: An overview of boots +Up: Linux System Administrators' Guide + Previous: The buffer cache +

+

Boots And Shutdowns

+

+  +

+

+ +Start me up
+Ah...you've got to...you've got to
+Never, never never stop
+Start it up
+Ah...start it up, never, never, never
+ You make a grown man cry,
+ you make a grown man cry
+(Rolling Stones)
+

+  +  +

+ This section explains what goes on when a Linux system is + brought up and taken down, and how it should be done properly. + If proper procedures are not followed, files might be corrupted + or lost. +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node67.html b/sag-0.6.1-www/Invisible/sag-0.6/node67.html new file mode 100644 index 0000000..6a13703 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node67.html @@ -0,0 +1,72 @@ + + + + +An overview of boots and shutdowns + + + + + + + + next up previous contents index
+ Next: The boot process in +Up: Boots And Shutdowns + Previous: Boots And Shutdowns +

+

An overview of boots and shutdowns

+

+ The act of turning on a computer system and causing its operating + system to be loadedgif is called booting. The name + comes from an image of the computer pulling itself up from its + bootstraps, but the act itself slightly more realistic. +  +  +

+ During bootstrapping, the computer first loads + a small piece of code called the bootstrap loader, + which in turn loads and starts + the operating system. The bootstrap loader is usually + stored in a fixed location on a hard disk or a floppy. The + reason for this two step process is that the operating system + is big and complicated, but the first piece of code that the + computer loads must be very small (a few hundred bytes), to avoid + making the firmware unnecessarily complicated. +  +

+ Different computers do the bootstrapping differently. For PC's, + the computer (its BIOS) reads in the first sector (called + the boot sector) of a floppy or hard disk. + The bootstrap loader + is contained within this sector. It loads the operating + system from elsewhere on the disk (or from some other place). +  +

+ After Linux has been loaded, it initializes the hardware and + device drivers, and then runs init . init  + starts other processes to allow users to log in, and do things. + The details of this part will be discussed below. +

+ In order to shut down a Linux system, first all processes + are told to terminate (this makes them close any files and + do other necessary things to keep things tidy), then filesystems + and swap areas are unmounted, and finally a message is printed + to the console that the power can be turned off. If the proper + procedure is not followed, terrible things can and will happen; + most importantly, the filesystem buffer cache might not be flushed, + which means that all data in it is lost and the filesystem on + disk is inconsistent, and therefore possibly unusable. +  +  +

+

next up previous contents index
+ Next: The boot process in +Up: Boots And Shutdowns + Previous: Boots And Shutdowns +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node68.html b/sag-0.6.1-www/Invisible/sag-0.6/node68.html new file mode 100644 index 0000000..3bd79e3 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node68.html @@ -0,0 +1,224 @@ + + + + +The boot process in closer look + + + + + + + + next up previous contents index
+ Next: More about shutdowns +Up: Boots And Shutdowns + Previous: An overview of boots +

+

The boot process in closer look

+

+  +

+ You can boot Linux either from a floppy or from the hard + disk. The installation section in the Installation and + Getting Started guide ([Wel]) + tells you how to install Linux so you can boot it the way + you want to. +

+ When a PC is booted, the BIOS will do various tests to + check that everything looks all right,gif and + will then start the actual booting. It will choose a disk + drive (typically the first floppy drive, if there is a floppy + inserted, otherwise the first hard disk, if one is installed + in the computer; the order might be configurable, however) + and will then read its very first sector. This is + called the boot sector; for a hard disk, it is also + called the master boot record, since a hard disk can + contain several partitions, each with their own boot sectors. +  +  +  +  +  +  +

+ The boot sector contains a small program (small enough to fit into + one sector) whose responsibility is to read the actual operating + system from the disk and start it. When booting Linux from + a floppy disk, the boot sector contains code that just reads + the first few hundred blocks (depending on the actual + kernel size, of course) to a predetermined place in memory. + On a Linux boot floppy, there is no filesystem, the kernel + is just stored in consecutive sectors, since this simplifies + the boot process. It is possible, however, to boot from a + floppy with a filesystem, by using LILO, the LInux LOader. +  +  +

+ When booting from the hard disk, the code in the master boot + record will examine the partition table (also in the master boot + record), identify the active + partition (the partition that is marked to be bootable), read + the boot sector from that partition, and then start the code + in that boot sector. The code in the partition's boot sector + does what a floppy disk's boot sector does: it will read in + the kernel from the partition and start it. The details vary, + however, since it is generally not useful to have a separate + partition for just the kernel image, so the code in the + partition's boot sector can't just read the disk in sequential + order, it has to find the sectors wherever the filesystem has + put them. There are several ways around this problem, but the + most common way is to use LILO. (The details about how to do + this are irrelevant for this discussion, however; see the LILO + documentation for more information; it is most thorough.) +  +  +  +  +  +

+ When booting with LILO, it will normally go right ahead and + read in and boot the default kernel. It is also possible to + configure LILO to be able to boot one of several kernels, or + even other operating systems than Linux, and it is possible + for the user to choose which kernel or operating system is to + be booted at boot time. LILO can be configured so that if one + holds down the alt, shift, or ctrl key at + boot time (when LILO is loaded), LILO will ask what is to + be booted and not boot the default right away. Alternatively, + LILO can be configured so that it will always ask, with an + optional timeout that will cause the default kernel to be + booted. +

+ With LILO, it is also possible to give a kernel command + line argument, after the name of the kernel or operating + system. +

+ META: The are other boot loaders than LILO. Information about + them will be added in some future version. loadlin. +

+ Booting from floppy and from hard disk have both their + advantages, but generally booting from the hard disk is + nicer, since it avoids the hassle of playing around with + floppies. It is also faster. However, it can be more + troublesome to install the system to boot from the hard + disk, so many people will first boot from floppy, then, when + the system is otherwise installed and working well, will + install LILO and start booting from the hard disk. +

+ After the Linux kernel has been read into the memory, by + whatever means, and is started for real, roughly the following + things happen: +

+

next up previous contents index
+ Next: More about shutdowns +Up: Boots And Shutdowns + Previous: An overview of boots +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node69.html b/sag-0.6.1-www/Invisible/sag-0.6/node69.html new file mode 100644 index 0000000..8ef46b2 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node69.html @@ -0,0 +1,136 @@ + + + + +More about shutdowns + + + + + + + + next up previous contents index
+ Next: Rebooting +Up: Boots And Shutdowns + Previous: The boot process in +

+

More about shutdowns

+

+ It is important to follow the correct procedures when you shut + down a Linux system. If you fail do so, your filesystems probably + will become trashed and the files probably will become scrambled. + This is because Linux has a disk cache that won't write things + to disk at once, but only at intervals. This greatly improves + performance but also means that if you just turn off the power + at a whim the cache may hold a lot of data and that what is on + the disk may not be a fully working filesystem (because only + some things have been written to the disk). +  +  +  +  +

+ Another reason against just flipping the power switch is that + in a multi-tasking system there can be lots of things going on + in the background, and shutting the power can be quite + disastrous. By using the proper shutdown sequence, you ensure + that all background processes can save their data. +  +

+ The command for properly shutting down a Linux system is + shutdown . It is usually used in one of two ways. +  +

+ If you are running a system where you are the only user, the + usual way of using shutdown  is to quit all running programs, + log out on all virtual consoles, log in as root on one + of them (or stay logged in as root if you already are, + but you should change to the root directory, to avoid problems + with unmounting), then give the command + shutdown -h now  + (substitute now with a plus sign and a number in minutes + if you want a delay, though you usually don't on a single user + system). +

+ Alternatively, if your system has many users, use the command + shutdown -h +time message, where time + is the + time in minutes until the system is halted, and message + is a short explanation of why the system is shutting down. +

+# shutdown -h +10 'We will install a new disk. System should
+> be back on-line in three hours.'
+# +
+ This will warn everybody that the system will shut + down in ten minutes, and that they'd better get lost or lose + data. The warning is printed to + every terminal on which someone is logged in, including all + xterm s: +
+Broadcast message from root (ttyp0) Wed Aug 2 01:03:25 1995...
+
+We will install a new disk. System should
+be back on-line in three hours.
+The system is going DOWN for system halt in 10 minutes !! +
+ The warning is automatically repeated a few times before the + boot, with shorter and shorter intervals as the time runs out. +  +

+ When the real shutting down starts after any + delays, all filesystems (except the root one) are unmounted, + user processes (if anybody is still logged in) are killed, + daemons are shut down, all filesystem are unmounted, + and generally everything settles down. + When that is done, init  prints out a message that + you can power down the machine. Then, and only then, + should you move your fingers towards the power switch. +  +

+ Sometimes, although rarely on any good system, it is + impossible to shut down properly. For instance, if the kernel + panics and crashes and burns and generally misbehaves, it + might be completely impossible to give any new commands, hence + shutting down properly is somewhat difficult, and just about + everything you can do is hope that nothing has been too + severely damaged and turn off the power. If the troubles are a + bit less severe (say, somebody hit your keyboard with + an axe), and the kernel and the update  program still run + normally, it is probably a good idea to wait a couple of + minutes to give update  a chance to flush the buffer + cache, and only cut the power after that. +  +  +  +  +  +  +  +

+ Some people like to shut down using the command + sync gif + three times, waiting for the disk I/O to stop, then turn off + the power. If there are no running programs, this is about + equivalent to using shutdown . However, it does not + unmount any filesystems and this can lead to problems with the + ext2fs ``clean filesystem'' flag. The triple-sync method is + not recommended. +  +

+ (In case you're wondering: the reason for three syncs is + that in the early days of UNIX, when the commands were + typed separately, that usually gave sufficient time for most + disk I/O to be finished.) +

+

next up previous contents index
+ Next: Rebooting +Up: Boots And Shutdowns + Previous: The boot process in +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node7.html b/sag-0.6.1-www/Invisible/sag-0.6/node7.html new file mode 100644 index 0000000..20297e9 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node7.html @@ -0,0 +1,82 @@ + + + + +Important parts of the kernel + + + + + + + + next up previous contents index
+ Next: Major services in a +Up: Overview of a Linux + Previous: Various parts of an +

+

Important parts of the kernel

+

+ The Linux kernel consists of several important parts: process + management, memory management, hardware device drivers, filesystem + drivers, network management, and various other bits and pieces. + Figure 2.1 shows some of them. +  +  +  +  +  +

+

  figure147
+Figure 2.1: Some of the more important parts of the Linux kernel.
+

+

+ Probably the most important parts of the kernel (nothing else + works without them) are memory management and + process management. Memory management takes care of assigning + memory areas and swap space areas to processes, parts of the + kernel, and for the buffer cache. Process management creates + processes, and implements multitasking by switching the + active process on the processor. +  +  +  +

+ At the lowest level, the kernel contains a hardware device + driver for each kind of + hardware it supports. Since the world is full of different + kinds of hardware, the number of hardware device drivers is + large. There are often many otherwise similar pieces of + hardware that differ in how they are controlled by software. + The similarities make it possible to have general classes + of drivers that support similar operations; each member of + the class has the same interface to the rest of the kernel + but differs in what it needs to do to implement them. For + example, all disk drivers look alike to the rest of the + kernel, i.e., they all have operations like `initialize the + drive', `read sector N', and `write sector N'. +

+ Some software services provided by the kernel itself have similar + properties, and can therefore be abstracted into classes. + For example, the various network protocols have been + abstracted into one programming interface, the BSD socket library. + Another example is the virtual filesystem (VFS) layer + that abstracts the filesystem operations away from their + implementation. Each filesystem type provides an implementation + of each filesystem operation. When some entity tries to + use a filesystem, the request goes via the VFS, which routes + the request to the proper filesystem driver. +  +  +  +

+

next up previous contents index
+ Next: Major services in a +Up: Overview of a Linux + Previous: Various parts of an +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node70.html b/sag-0.6.1-www/Invisible/sag-0.6/node70.html new file mode 100644 index 0000000..1db7174 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node70.html @@ -0,0 +1,44 @@ + + + + +Rebooting + + + + + + + + next up previous contents index
+ Next: Single user mode +Up: Boots And Shutdowns + Previous: More about shutdowns +

+

Rebooting

+

+ Rebooting means booting the system again. This can be accomplished + by first shutting it down completely, turning power off, and then + turning it back on. A simpler way is to ask shutdown  to + reboot the system, instead of merely halting it. This + is accomplished by using the -r option to shutdown, for + example, by giving the command shutdown -r now. +  +

+ Most Linux systems run shutdown -r now + when ctrl-alt-del is pressed on the keyboard. This reboots the + system. The action on ctrl-alt-del is configurable, however, and + it might be better to allow for some delay before the reboot + on a multiuser machine. Systems that are physically accessible + to anyone might even be configured to do nothing when ctrl-alt-del + is pressed. +  +  +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node71.html b/sag-0.6.1-www/Invisible/sag-0.6/node71.html new file mode 100644 index 0000000..e4b6f9f --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node71.html @@ -0,0 +1,35 @@ + + + + +Single user mode + + + + + + + + next up previous contents index
+ Next: Emergency boot floppies +Up: Boots And Shutdowns + Previous: Rebooting +

+

Single user mode

+

+ The shutdown command can also be used to bring the system + down to single user mode, in which no one can log in, but + root can use the console. This is useful for + system administration tasks that can't be done while the system + is running normally. Single user mode is discussed more + thoroughly in chapter gif. +  +  +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node72.html b/sag-0.6.1-www/Invisible/sag-0.6/node72.html new file mode 100644 index 0000000..b01cecd --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node72.html @@ -0,0 +1,63 @@ + + + + +Emergency boot floppies + + + + + + + + next up previous contents index
+ Next: init +Up: Boots And Shutdowns + Previous: Single user mode +

+

Emergency boot floppies

+

+ It is not always possible to boot a computer from the hard disk. + For example, if you make a mistake in configuring LILO, you might + make your system unbootable. For these situations, you need an + alternative way of booting that will always work (as long as the + hardware works). For typical PC's, this means booting from the + floppy drive. +  +  +

+ Most Linux distributions allow one to create an emergency + boot floppy during installation. It is a good idea to do this. + However, some such boot disks contain only the kernel, and assume + you will be using the programs on the distribution's installation + disks to fix whatever problem you have. Sometimes those programs + aren't enough; for example, you might have to restore some files + from backups made with software not on the installation disks. +  +  +  +

+ Thus, it might be necessary to create a custom root floppy as well. + The Bootdisk HOWTO by Graham Chapman ([Cha]) + contains instructions for doing this. + You must, of course, remember to keep your emergency boot + and root floppies up to date. +  +

+ You can't use the floppy drive you use to mount the root floppy + for anything else. This can be inconvenient if you only have one + floppy drive. However, if you have enough memory, you + can configure your boot floppy to load the root + disk to a ramdisk (the boot floppy's kernel needs to be specially + configured for this). + Once the root floppy has been loaded into the ramdisk, the + floppy drive is free to mount other disks. +  +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node73.html b/sag-0.6.1-www/Invisible/sag-0.6/node73.html new file mode 100644 index 0000000..88b00d4 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node73.html @@ -0,0 +1,53 @@ + + + + +init + + + + + + + + next up previous contents index
+ Next: init comes first +Up: Linux System Administrators' Guide + Previous: Emergency boot floppies +

+ 

init

+

+  +

+

+ +Uuno on numero yksi
+

+

+ This chapter describes the init  process, which is + the first user level process started by the kernel. init  + has many important duties, such as starting getty  (so that + users can log in), implementing run levels, and taking care + of orphaned processes. This chapter explains how init  + is configured and how you can make use of the different run + levels. +

+  +  +  +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node74.html b/sag-0.6.1-www/Invisible/sag-0.6/node74.html new file mode 100644 index 0000000..7ed9108 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node74.html @@ -0,0 +1,74 @@ + + + + +init comes first + + + + + + + + next up previous contents index
+ Next: Configuring init to start +Up: init + Previous: init +

+ 

init comes first

+

+ init  is one of those programs that are absolutely essential + to the operation of a Linux system, but that you still can mostly + ignore. A good Linux distribution will come with a configuration + for init  that will work for most systems, and on these + systems there is nothing you need to do about init . Usually, + you only need to worry about init  if you hook up serial + terminals, dial-in (not dial-out) modems, or if you want to change + the default run level. +

+ When the kernel has started itself (has been loaded into memory, + has started running, and has initialized all device drivers and + data structures and such), it finishes its own part of the boot + process by starting a user level program, init . Thus, + init  is always the first process (its process number is + always 1). +

+ The kernel looks for init  in a few locations that have + been historically used for it, but the proper location for it + (on a Linux system) is /sbin/init . If the kernel can't + find init , it tries to run /bin/sh , and if that + also fails, the startup of the system fails. +

+ When init  starts, it finishes the boot process by doing + a number of administrative tasks, such as checking filesystems, + cleaning up /tmp , starting various services, and starting + a getty  for each terminal and virtual console where users + should be able to log in (see chapter 8). +

+ After the system is properly up, init  restarts + getty  for each terminal after a user has logged out (so + that the next user can log in). init  also adopts orphan + processes: when a process starts a child process and dies before + its child, the child immediately becomes a child of init . + This is important for various technical reasons, but it is good + to know it, since it makes it easier to understand process lists + and process tree graphs.gif +

+ There are a few variants of init  available. Most Linux + distributions use sysvinit  (written by Miquel van + Smoorenburg), which is based on the System V init  design. + The BSD versions of Unix have a different init . The primary + difference is run levels: System V has them, BSD does not + (at least traditionally). This difference is not essential. + We'll look at sysvinit  only. +

+

next up previous contents index
+ Next: Configuring init to start +Up: init + Previous: init +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node75.html b/sag-0.6.1-www/Invisible/sag-0.6/node75.html new file mode 100644 index 0000000..9f8e02b --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node75.html @@ -0,0 +1,96 @@ + + + + +Configuring init to start getty: the /etc/inittab file + + + + + + + + next up previous contents index
+ Next: Run levels +Up: init + Previous: init comes first +

+ 

Configuring init  to start getty : the /etc/inittab file

+

+ When it starts up, init  reads the /etc/inittab  + configuration file. While the system is running, it will + re-read it, if sent the HUP signal;gif this feature makes it + unnecessary to boot the system to make changes to the init  + configuration take effect. +

+ The /etc/inittab  file is a bit complicated. We'll start + with the simple case of configuring getty  lines. Lines in + /etc/inittab  consist of four colon-delimited fields: +

id:runlevels:action:process +
+ The fields are described below. In addition, /etc/inittab  + can contain empty lines, and lines that begin with a number + sign (`#'); these are both ignored. +

+

id +
This identifies the line in the file. For + getty  lines, it specifies the terminal + it runs on (the characters after /dev/tty  + in the device file name). For other lines, + it doesn't matter (except for length restrictions), + but it should be unique. +

+

runlevels +
+ The run levels the line should be considered + for. The run levels are given as single digits, + without delimiters. (Run levels are described + in the next section.) +

+

action +
What action should be taken by the line, e.g., + respawn to run the command in the + next field again, when it exits, or once + to run it just once. +

+

process +
The command to run. +

+

+

+ To start a getty  on the first virtual terminal + (/dev/tty1 ), in all the normal multi-user run levels + (2-5), one would write the following line: +

+1:2345:respawn:/sbin/getty 9600 tty1 +
+ The first field says that this is the line for /dev/tty1 . + The second field says that it applies to run levels 2, 3, 4, + and 5. The third field means that the command should be run + again, after it exits (so that one can log in, log out, and + then log in again). The last field is the command that runs + getty  on the first virtual terminal.gif +

+ If you wanted to add terminals or dial-in modem lines to a system, + you'd add more lines to /etc/inittab , one for each terminal + or dial-in line. For more details, see the manual pages + init (8), inittab (5), and getty (8). +

+ If a command fails when it starts, and init  is configured + to restart it, it will use a lot of system resources: + init  starts it, it fails, init  starts it, it fails, + init  starts it, it fails, and so on, ad infinitum. To + prevent this, init  will keep track of how often it restarts + a command, and if the frequency grows to high, it will delay for + five minutes before restarting again. +

+

next up previous contents index
+ Next: Run levels +Up: init + Previous: init comes first +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node76.html b/sag-0.6.1-www/Invisible/sag-0.6/node76.html new file mode 100644 index 0000000..3fc9d01 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node76.html @@ -0,0 +1,80 @@ + + + + +Run levels + + + + + + + + next up previous contents index
+ Next: Special configuration in /etc/inittab +Up: init + Previous: Configuring init to start +

+

Run levels

+

+ A run level is a state of init  and the whole + system that defines what system services are operating. Run + levels are identified by numbers, see table 7.1. + There is no consensus of how to use the user defined run levels + (2 through 5). Some system administrators use run levels to + define which subsystems are working, e.g., whether X is running, + whether the network is operational, and so on. Others have all + subsystems always running or start and stop them individually, + without changing run levels, since run levels are too coarse + for controlling their systems. You need to decide for yourself, + but it might be easiest to follow the way your Linux distribution + does things. +

+

  table2241
+Table 7.1: Run level numbers
+

+

+ Run levels are configured in /etc/inittab  by lines like + the following: +

+l2:2:wait:/etc/init.d/rc 2 +
+ The first field is an arbitrary label, the second one means + that this applies for run level 2. The third field means that + init  should run the command in the fourth field once, + when the run level is entered, and that init  should wait + for it to complete. The + /etc/init.d/rc  command runs whatever commands are necessary + to start and stop services to enter run level 2. +

+ The command in the fourth field does all the hard work of + setting up a run level. It starts services that aren't already + running, and stops services that shouldn't be running in the + new run level any more. Exactly what the command is, and how + run levels are configured, depends on the Linux distribution. +

+ When init  starts, it looks for a line in /etc/inittab  + that specifies the default run level: +

+id:2:initdefault: +
+ You can ask init  to go to a non-default + run level at startup by giving the kernel a command line + argument of single or emergency.gif This allows you to choose + the single user mode (run level 1), which is described in + section 7.5. +

+ While the system is running, the telinit  command can change + the run level. When the run level is changed, init  runs + the relevant command from /etc/inittab . +

+

next up previous contents index
+ Next: Special configuration in /etc/inittab +Up: init + Previous: Configuring init to start +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node77.html b/sag-0.6.1-www/Invisible/sag-0.6/node77.html new file mode 100644 index 0000000..b3e72ce --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node77.html @@ -0,0 +1,58 @@ + + + + +Special configuration in /etc/inittab + + + + + + + + next up previous contents index
+ Next: Booting in single user +Up: init + Previous: Run levels +

+ 

Special configuration in /etc/inittab

+

+ The /etc/inittab  has some special features that allow + init  to react to special circumstances. These special + features are marked by special keywords in the third field. + Some examples: +

+

powerwait +
+ Allows init  to shut the system down, when the + power fails. This assumes the use of a UPS, and software + that watches the UPS and informs init  that the + power is off. +

+

ctrlaltdel +
+ Allows init  to reboot the system, when the user + presses control-alt-del on the console keyboard. + Note that the system administrator can configure the + reaction to C-A-D to be something else instead, + e.g., to be ignored, if the system is in a public + location.gif +

+

sysinit +
+ Command to be run when the system is booted. This command + usually cleans up /tmp , for example. +

+

+

+ The list above is not exhaustive. See your inittab (5) + manual page for all possibilities, and for details on how to use + the above ones. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node78.html b/sag-0.6.1-www/Invisible/sag-0.6/node78.html new file mode 100644 index 0000000..176d85e --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node78.html @@ -0,0 +1,69 @@ + + + + +Booting in single user mode + + + + + + + + next up previous contents index
+ Next: Logging In And Out +Up: init + Previous: Special configuration in /etc/inittab +

+

Booting in single user mode

+

+  +

+ An important run level is single user mode (run level 1), + in which only the system administrator is using the machine + and as few system services--including logins--as possible are + running. Single user mode is necessary for a few administrative + tasks,gif such as running fsck  on a /usr  + partition--this requires that the partition be unmounted, + and that can't happen, unless just about all system services + are killed. +

+ A running system can be taken to single user mode by using + telinit  to request run level 1. At bootup, it can be + entered by giving the word single or emergency + on the kernel command line: the kernel gives the command line + to init  as well, and init  understands from that + word that it shouldn't use the default run level. (The kernel + command line is entered in a way that depends on how you boot + the system.) +

+ Booting into single user mode is sometimes necessary so that + one can run fsck  by hand, before anything mounts or + otherwise touches a broken /usr  partition (any activity + on a broken filesystem is likely to break it more, so fsck  + should be run as soon as possible). +

+ The bootup scripts init  runs will automatically enter single + user mode, if the automatic fsck  at bootup fails. This is an + attempt to prevent the system from using a filesystem that is so + broken that fsck  can't fix it automatically. Such breakage + is relatively rare, and usually involves a broken hard disk or + an experimental kernel release, but it's good to be prepared. +

+ As a security measure, a properly configured system will ask + for the root password before starting the shell in + single user mode. Otherwise, it would be simple to just enter + a suitable line to LILO to get in as root. (This will + break if /etc/passwd  has been broken by filesystem problems, + of course, and in that case you'd better have a boot floppy handy.) +

+

next up previous contents index
+ Next: Logging In And Out +Up: init + Previous: Special configuration in /etc/inittab +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node79.html b/sag-0.6.1-www/Invisible/sag-0.6/node79.html new file mode 100644 index 0000000..1f58b52 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node79.html @@ -0,0 +1,46 @@ + + + + +Logging In And Out + + + + + + + + next up previous contents index
+ Next: Logins via terminals +Up: Linux System Administrators' Guide + Previous: Booting in single user +

+

Logging In And Out

+

+  +

+

+ + This chapter needs a quote. Suggestions, anyone?
+

+

+ This section describes what happens when a user logs in or out. + The various interactions of background processes, log files, + configuration files, and so on are described in some detail. +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node8.html b/sag-0.6.1-www/Invisible/sag-0.6/node8.html new file mode 100644 index 0000000..7942fd2 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node8.html @@ -0,0 +1,43 @@ + + + + +Major services in a UNIX system + + + + + + + + next up previous contents index
+ Next: init +Up: Overview of a Linux + Previous: Important parts of the +

+

Major services in a UNIX system

+

+ This section describes some of the more important UNIX services, + but without much detail. They are described + more thoroughly in later chapters. +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node80.html b/sag-0.6.1-www/Invisible/sag-0.6/node80.html new file mode 100644 index 0000000..60dae28 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node80.html @@ -0,0 +1,71 @@ + + + + +Logins via terminals + + + + + + + + next up previous contents index
+ Next: Logins via the network +Up: Logging In And Out + Previous: Logging In And Out +

+

Logins via terminals

+

+ Figure 8.1 shows how logins happen + via terminals. First, init  makes sure there is a + getty  program for the terminal connection (or + console). getty  listens at the terminal and waits for + the user to notify that he is ready to login in (this usually + means that the user must type something). When it notices a + user, getty  outputs + a welcome message (stored in /etc/issue ), and prompts for + the username, and finally runs the login  program. + login  gets the username as a parameter, and prompts the + user for the password. If these match, login  + starts the shell configured for the user; else it just exits + and terminates the process (perhaps after giving the user + another chance at entering the username and password). + init  notices that the + process terminated, and starts a new getty  for the + terminal. +

+

  figure2514
+Figure 8.1: Logins via terminals: the interaction of init , getty , + login , and the shell.
+

+

+ Note that the only new process is the one created by init  + (using the fork  system call); + getty  and login  only replace the program running + in the process (using the exec  system call). +

+ A separate program, for noticing the user, is needed for serial + lines, since it can be (and traditionally was) complicated to + notice when a terminal becomes active. getty  also adapts + to the speed and other settings of the connection, which is + important especially for dial-in connections, where these + parameters may change from call to call. +

+ There are several versions of getty  and init  + in use, all with their good and bad points. It is a good idea + to learn about the versions on your system, and also about the + other versions (you could use the Linux Software Map to search + them). If you don't have dial-in's, you probably don't have to + worry about getty , but init  is still important. +

+

next up previous contents index
+ Next: Logins via the network +Up: Logging In And Out + Previous: Logging In And Out +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node81.html b/sag-0.6.1-www/Invisible/sag-0.6/node81.html new file mode 100644 index 0000000..4b7df40 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node81.html @@ -0,0 +1,75 @@ + + + + +Logins via the network + + + + + + + + next up previous contents index
+ Next: What login does +Up: Logging In And Out + Previous: Logins via terminals +

+

Logins via the network

+

+ Two computers in the same network are usually linked via a single + physical cable. When they communicate over the network, the programs + in each computer that take part in the communication are linked + via a virtual connection, a sort of imaginary cable. + As far as the programs at either end of the virtual connection + are concerned, they have a monopoly on their own cable. However, + since the cable is not real, only imaginary, the operating systems + of both computers can have several virtual connections share + the same physical cable. This way, using just a single cable, + several programs can communicate without having to know of or + care about the other communications. It is even possible to + have several computers use the same cable; the virtual + connections exist between two computers, and the other computers + ignore those connections that they don't take part in. +

+ That's a complicated and over-abstracted description of the + reality. It might, however, be good enough to understand + the important reason why network logins are somewhat different + from normal logins. The virtual connections are established + when there are two programs on different computers that + wish to communicate. Since it is in principle possible to + login from any computer in a network to any other computer, + there is a huge number of potential virtual communications. + Because of this, it is not practical to start a getty  + for each potential login. +

+ There is a single process inetd (corresponding + to getty ) that handles all network logins. + When it notices an incoming network login (i.e., it notices + that it gets a new virtual connection to some other computer), + it starts a new process to handle that single login. The + original process remains and continues to listen for new + logins. +

+ To make things a bit more complicated, there is more than + one communication protocol for network logins. The two + most important ones are telnet  and rlogin . In + addition to logins, there are many other virtual connections + that may be made (for FTP, Gopher, HTTP, and other network services). + It would be ineffective to have a separate process listening + for a particular type of connection, so instead there is only + one listener that can recognize the type of the connection and + can start the correct type of program to provide the service. + This single listener is called inetd ; see the + ``Linux Network Administrators' Guide'' for more information. +

+

next up previous contents index
+ Next: What login does +Up: Logging In And Out + Previous: Logins via terminals +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node82.html b/sag-0.6.1-www/Invisible/sag-0.6/node82.html new file mode 100644 index 0000000..54ab87b --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node82.html @@ -0,0 +1,65 @@ + + + + +What login does + + + + + + + + next up previous contents index
+ Next: X and xdm +Up: Logging In And Out + Previous: Logins via the network +

+ 

What login does

+

+ The login  program takes care of authenticating the user + (making sure that the username and password match), and of + setting up an initial environment for the user by setting + permissions for the serial line and starting the shell. +

+ Part of the initial setup is outputting the contents of the + file /etc/motd  (short for message of the day) and checking + for electronic mail. These can be disabled by creating a file + called .hushlogin  in the user's home directory. +

+ If the file /etc/nologin  exists, logins are + disabled. That file is typically created by shutdown  + and relatives. login  checks for this file, and will + refuse to accept a login if it exists. If it does exist, + login  outputs its contents to the terminal before it quits. +

+ login  logs all failed login attempts in a system log file + (via syslog ). It also logs all logins by root. + Both of these can be useful when tracking down intruders. +

+ Currently logged in people are listed in /var/run/utmp . + This file is valid only until the system is next rebooted or shut + down; it is cleared when the system is booted. It lists each + user and the terminal (or network connection) he is using, along + with some other useful information. The who , w , and + other similar commands look in utmp  to see who are logged in. +

+ All successful logins are recorded into /var/log/wtmp . + This file will grow without limit, so it must be cleaned + regularly, for example by having a weekly cron  job + to clear it.gif The last  command browses wtmp . +

+ Both utmp  and wtmp  are in a binary format (see the + utmp  manual page); it is unfortunately not convenient + to examine them without special programs. +

+

next up previous contents index
+ Next: X and xdm +Up: Logging In And Out + Previous: Logins via the network +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node83.html b/sag-0.6.1-www/Invisible/sag-0.6/node83.html new file mode 100644 index 0000000..0a6d6cf --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node83.html @@ -0,0 +1,28 @@ + + + + +X and xdm + + + + + + + + next up previous contents index
+ Next: Access control +Up: Logging In And Out + Previous: What login does +

+

X and xdm

+

+ META: X implements logins via xdm; also: xterm -ls +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node84.html b/sag-0.6.1-www/Invisible/sag-0.6/node84.html new file mode 100644 index 0000000..2165353 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node84.html @@ -0,0 +1,70 @@ + + + + +Access control + + + + + + + + next up previous contents index
+ Next: Shell startup +Up: Logging In And Out + Previous: X and xdm +

+

Access control

+

+ The user database is traditionally contained in the + /etc/passwd  file. Some systems use shadow passwords, + and have moved the passwords to /etc/shadow . + Sites with many computers that share the accounts use + NIS or some other method to store the user database; they might + also automatically copy the database from one central location + to all other computers. +

+ The user database contains not only the passwords, but also + some additional information about the users, such as their + real names, home directories, and login shells. This other + information needs to be public, so that anyone can read it. + Therefore the password is stored encrypted. This does have + the drawback that anyone with access to the encrypted password + can use various cryptographical methods to guess it, without + trying to actually log into the computer. Shadow passwords + try to avoid this by moving the password into another file, + which only root can read (the password is still + stored encrypted). However, installing shadow passwords later + onto a system that did not support them can be difficult. +

+ With or without passwords, it is important to make sure that + all passwords in a system are good, i.e., not easily guessable. + The crack  program can be used to crack passwords; any + password it can find is by definition not a good one. While + crack  can be run by intruders, it can also be run by + the system adminstrator to avoid bad passwords. Good passwords + can also be enforced by the passwd  program; this is + in fact more effective in CPU cycles, since cracking passwords + requires quite a lot of computation. +

+ The user group database is kept in /etc/group ; for systems + with shadow passwords, there can be a /etc/shadow.group . +

+ root usually can't login via most terminals or the + network, only via terminals listed in the /etc/securetty  + file. This makes it necessary to get physical access to + one of these terminals. It is, however, possible to log in + via any terminal as any other user, and use the su  command + to become root. +

+

next up previous contents index
+ Next: Shell startup +Up: Logging In And Out + Previous: X and xdm +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node85.html b/sag-0.6.1-www/Invisible/sag-0.6/node85.html new file mode 100644 index 0000000..8a3d895 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node85.html @@ -0,0 +1,41 @@ + + + + +Shell startup + + + + + + + + next up previous contents index
+ Next: Managing user accounts +Up: Logging In And Out + Previous: Access control +

+

Shell startup

+

+ When an interactive login shell starts, it automatically executes + one or more pre-defined files. Different shells execute different + files; see the documentation of each shell for further information. +

+ Most shells first run some global file, for example, the Bourne + shell (/bin/sh ) and its derivatives execute /etc/profile ; + in addition, they execute .profile  in the user's home directory. + /etc/profile  + allows the system administrator to have set up a common user + environment, especially by setting the PATH to include local + command directories in addition to the normal ones. On the other + hand, .profile  allows the user to customize the environment + to his own tastes by overriding, if necessary, the default + environment. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node86.html b/sag-0.6.1-www/Invisible/sag-0.6/node86.html new file mode 100644 index 0000000..eeb1c60 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node86.html @@ -0,0 +1,54 @@ + + + + +Managing user accounts + + + + + + + + next up previous contents index
+ Next: What's an account? +Up: Linux System Administrators' Guide + Previous: Shell startup +

+

Managing user accounts

+

+  +

+

+ + The similarities of sysadmins and drug dealers:
+ both measure stuff in K's, and both have users.
+ (Old, tired computer joke.)
+

+

+ This chapter explains how to create new user accounts, how to + modify the properties of those accounts, and how to remove the + accounts. Different Linux systems have different tools for + doing this. +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node87.html b/sag-0.6.1-www/Invisible/sag-0.6/node87.html new file mode 100644 index 0000000..84d67db --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node87.html @@ -0,0 +1,45 @@ + + + + +What's an account? + + + + + + + + next up previous contents index
+ Next: Creating a user +Up: Managing user accounts + Previous: Managing user accounts +

+

What's an account?

+

+ When a computer is used by many people it is usually + necessary to differentiate between the users, for + example, so that their private files can be kept + private. This is important even if the computer can + only be used by a single person at a time, as with + most microcomputers.gif Thus, each + user is given a unique username, and that name is used + to log in. +

+ There's more to a user than just a name, however. An + account is all the files, resources, and + information belonging to one user. The term hints at + banks, and in a commercial system each account usually + has some money attached to it, and that money vanishes + at different speeds depending on how much the user + stresses the system. For example, disk space might have + a price per megabyte and day, and processing time might + have a price per second. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node88.html b/sag-0.6.1-www/Invisible/sag-0.6/node88.html new file mode 100644 index 0000000..fe6ec2d --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node88.html @@ -0,0 +1,56 @@ + + + + +Creating a user + + + + + + + + next up previous contents index
+ Next: /etc/passwd and other informative +Up: Managing user accounts + Previous: What's an account? +

+

Creating a user

+

+ The Linux kernel itself treats users are mere numbers. + Each user is identified by a unique integer, the + user id or uid, because numbers are + faster and easier for a computer to process than textual + names. A separate database outside the kernel assigns + a textual name, the username, to each user id. + The database contains additional information as well. +

+ To create a user, you need to add information about the + user to the user database, and create a home directory + for him. It may also be necessary to educate the user, + and set up a suitable initial environment for him. +

+ Most Linux distributions come with a program for creating + accounts. There are several such programs available. + Two command line alternatives are adduser  and + useradd ; there may be a GUI tool as well. Whatever + the program, the result is that there is little if any + manual work to be done. Even if the details are many and + intricate, these programs make everything seem trivial. + However, section 9.2.4 describes how + to do it by hand. +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node89.html b/sag-0.6.1-www/Invisible/sag-0.6/node89.html new file mode 100644 index 0000000..9d32b9e --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node89.html @@ -0,0 +1,63 @@ + + + + +/etc/passwd and other informative files + + + + + + + + next up previous contents index
+ Next: Picking numeric user and +Up: Creating a user + Previous: Creating a user +

+ 

/etc/passwd and other informative files

+

+ The basic user database in a Unix system is the text + file, /etc/passwd  (called the password + file), which lists all valid usernames and their + associated information. The file has one line per + username, and is divided into seven colon-delimited + fields: +

    +
  1. Username. +
  2. Password, in an encrypted form. +
  3. Numeric user id. +
  4. Numeric group id. +
  5. Full name or other description of account. +
  6. Home directory. +
  7. Login shell (program to run at login). +
+ The format is explained in more detail in passwd (5). +

+ Any user on the system may read the password file, so that + they can, for example, learn the name of another user. + This means that the password (the second field) is also + available to everyone. The password file encrypts the + password, so in theory there is no problem. However, the + encryption is breakable, especially if the password is weak + (e.g., it is short or it can be found in a dictionary). + Therefore it is not a good idea to have the password in + the password file. +

+ Many Linux systems have shadow passwords. This is + an alternative way of storing the password: the encrypted + password is stored in a separate file, /etc/shadow , + which only root can read. The /etc/passwd  + file only contains a special marker in the second field. + Any program that needs to verify a user is setuid, and + can therefore access the shadow password file. Normal + programs, which only use the other fields in the password + file, can't get at the password.gif +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node9.html b/sag-0.6.1-www/Invisible/sag-0.6/node9.html new file mode 100644 index 0000000..255e964 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node9.html @@ -0,0 +1,65 @@ + + + + +init + + + + + + + + next up previous contents index
+ Next: Logins from terminals +Up: Major services in a + Previous: Major services in a +

+ 

init

+

+ The single most important service in a UNIX system is provided + by init . init  is started as the first process of + every UNIX system, as the last thing the kernel does when it + boots. When init  starts, it continues the boot process + by doing various startup chores (checking and mounting filesystems, + starting daemons, etc). +  +  +  +

+ The exact list of things that init  + does depends on which flavor it is; there are several to choose + from. init  + usually provides the concept of single user mode, in which + no one can log in and root  uses a shell at the console; the usual + mode is called multiuser mode. + Some flavors generalize this as run levels; single and + multiuser modes are considered to be two run levels, and there + can be additional ones as well, for example, to run X on the + console. +  +  +  +  +

+ In normal operation, init  makes sure getty s are + working (to allow users to log in), and to + adopt orphan processes (processes whose parent has died; in + UNIX all processes must be in a single tree, + so orphans must be adopted). +

+ When the system is shut down, it is init  that is in charge + of killing all + other processes, unmounting all filesystems and stopping the processor, + along with anything else it has been configured to do. +  +  +  +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node90.html b/sag-0.6.1-www/Invisible/sag-0.6/node90.html new file mode 100644 index 0000000..944b858 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node90.html @@ -0,0 +1,43 @@ + + + + +Picking numeric user and group ids + + + + + + + + next up previous contents index
+ Next: Initial environment: /etc/skel +Up: Creating a user + Previous: /etc/passwd and other informative +

+

Picking numeric user and group ids

+

+ On most systems it doesn't matter what the numeric user and + group ids are, but if you use the Network filesystem (NFS), + you need to have the same uid and gid on all systems. This + is because NFS also identifies users with the numeric uids. + If you aren't using NFS, you can let your account creation + tool pick them automatically. +

+ If you are using NFS, you'll have to be invent a mechanism + for synchronizing account information. One alternative is + to the NIS system (see [Kir]). +

+ META: this is wrong place? + However, you should try to avoid re-using numeric uid's + (and textual usernames), because the new owner of the uid + (or username) may get access to the old owner's files + (or mail, or whatever). +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node91.html b/sag-0.6.1-www/Invisible/sag-0.6/node91.html new file mode 100644 index 0000000..012fce5 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node91.html @@ -0,0 +1,47 @@ + + + + +Initial environment: /etc/skel + + + + + + + + next up previous contents index
+ Next: Creating a user by +Up: Creating a user + Previous: Picking numeric user and +

+ 

Initial environment: /etc/skel

+

+ When the home directory for a new user is created, it is + initialized with files from the /etc/skel  directory. + The system administrator can create files in /etc/skel  + that will provide a nice default environment for users. + For example, he might create a /etc/skel/.profile  that + sets the EDITOR environment variable to some editor that + is friendly towards new users. +

+ However, it is usually best to try to keep /etc/skel  + as small as possible, since it will be next to impossible + to update existing users' files. For example, if the name + of the friendly editor changes, all existing users would + have to edit their .profile . The system administrator + could try to do it automatically, with a script, but that + is almost certain going to break someone's file. +

+ Whenever possible, it is better to put + global configuration into global files, such as + /etc/profile . This way it is possible to update + it without breaking users' own setups. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node92.html b/sag-0.6.1-www/Invisible/sag-0.6/node92.html new file mode 100644 index 0000000..1d24df6 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node92.html @@ -0,0 +1,76 @@ + + + + +Creating a user by hand + + + + + + + + next up previous contents index
+ Next: Changing user properties +Up: Creating a user + Previous: Initial environment: /etc/skel +

+

Creating a user by hand

+  +

+ To create a new account manually, follow these steps: +

    +
  1. Edit /etc/passwd  with vipw (8) and add a + new line for the new account. Be careful with + the syntax. Do not edit directly with an + editor! vipw  locks the file, so that + other commands won't try to update it at the + same time. You should make the password field be + `*', so that it is impossible to log in. +
  2. Similarly, edit /etc/group  with vigr , if + you need to create a new group as well. +
  3. Create the home directory of the user with + mkdir . +
  4. Copy the files from /etc/skel  to the new home + directory. +
  5. Fix ownerships and permissions with chown  and + chmod . The -R option is most useful. + The correct permissions vary a little from one site + to another, but usually the following commands do + the right thing: +
    +cd /home/newusername
    +chown -R username.group .
    +chmod -R go=u,go-w .
    +chmod go= . +
    +
  6. Set the password with passwd (1). +
+

+ After you set the password in the last step, the account will + work. You shouldn't set it until everything else has been done, + otherwise the user may inadvertently log in while you're + still copying the files. +

+ It is sometimes necessary to create dummy + accountsgif that are not used by + people. For example, to set up an anonymous FTP server + (so that anyone can download files from it, without + having to get an account first), you need to create an + account called ftp. In such cases, it is usually + not necessary to set the password (last step above). + Indeed, it is better + not to, so that no-one can use the account, unless + they first become root, since root + can become any user. +

+

next up previous contents index
+ Next: Changing user properties +Up: Creating a user + Previous: Initial environment: /etc/skel +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node93.html b/sag-0.6.1-www/Invisible/sag-0.6/node93.html new file mode 100644 index 0000000..993e2c4 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node93.html @@ -0,0 +1,54 @@ + + + + +Changing user properties + + + + + + + + next up previous contents index
+ Next: Removing a user +Up: Managing user accounts + Previous: Creating a user by +

+

Changing user properties

+

+ There are a few commands for changing various + properties of an account (i.e., the relevant field + in /etc/passwd ): +

chfn  +
Change the full name field. +
chsh  +
Change the login shell. +
passwd  +
Change the password. +

+

+ The super-user may use these commands to change the + properties of any account. Normal users can only change + the properties of their own account. It may + sometimes be necessary to disable these commands (with + chmod ) for normal users, for example in an environment + with many novice users. +

+ Other tasks need to be done by hand. For example, to + change the username, you need to edit /etc/passwd  + directly (with vipw , remember). Likewise, to add + or remove the user to more groups, you need to edit + /etc/group  (with vigr ). Such tasks tend to + be rare, however, and should be done with caution: for + example, if + you change the username, e-mail will no longer reach the + user, unless you also create a mail alias.gif +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node94.html b/sag-0.6.1-www/Invisible/sag-0.6/node94.html new file mode 100644 index 0000000..80d22ad --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node94.html @@ -0,0 +1,51 @@ + + + + +Removing a user + + + + + + + + next up previous contents index
+ Next: Disabling a user temporarily +Up: Managing user accounts + Previous: Changing user properties +

+

Removing a user

+

+ To remove a user, you first remove all his files, + mailboxes, mail aliases, print jobs, cron  and + at  jobs, and all other references to the user. + Then you remove the relevant lines from /etc/passwd  + and /etc/group  (remember to remove the username from + all groups it's been added to). It may be a good idea + to first disable the account (see below), before you + start removing stuff, to prevent the user from using the + account while it is being removed. +

+ Remember that users may have files outside their home + directory. The find  command can find them: +

+find / -user username +
+ However, note that the above command will take a long + time, if you have large disks. If you mount network disks + (see section 2.3.8), you need to be careful so + that you won't trash the network or the server. +

+ Some Linux distributions come with special commands + to do this; look for deluser  or userdel . + However, it is easy to do it by hand as well, and the + commands might not do everything. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node95.html b/sag-0.6.1-www/Invisible/sag-0.6/node95.html new file mode 100644 index 0000000..09f8934 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node95.html @@ -0,0 +1,70 @@ + + + + +Disabling a user temporarily + + + + + + + + next up previous contents index
+ Next: Backups +Up: Managing user accounts + Previous: Removing a user +

+

Disabling a user temporarily

+

+ It is sometimes necessary to temporarily disable an account, + without removing it. For example, the user might not have paid + his fees, or the system administrator may suspect that a cracker + has got the password of that account. +

+ The best way to disable an account is to change its shell + into a special program that just prints a message. This + way, whoever tries to log into the account, will fail, + and will know why. The message can tell the user to + contact the system administrator so that any problems + may be dealt with. +

+ It would also be possible to change the username + or password to something else, but then the user + won't know what is going on. Confused users mean more + work.gif +

+ A simple way to create the special programs is to write + `tail scripts': +

#!/usr/bin/tail +2
+This account has been closed due to a security breach.
+Please call 555-1234 and wait for the men in black to arrive.
+ The first two characters (`#!') tell the kernel that + the rest of the line is a command that needs to be run to + interpret this file. The tail  command in this case + outputs everything except the first line to the standard + output. +

+ If billg is suspected of a security breach, + the system administrator would do something like this: +

+# chsh -s /usr/local/lib/no-login/security billg
+# su - tester
+This account has been closed due to a security breach.
+Please call 555-1234 and wait for the men in black to arrive.
+# +
+ The purpose of the su  is to test that the change worked, + of course. +

+ Tail scripts should be kept in a separate directory, + so that their names don't interfere with normal user + commands. +

+

+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node96.html b/sag-0.6.1-www/Invisible/sag-0.6/node96.html new file mode 100644 index 0000000..71c42c9 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node96.html @@ -0,0 +1,52 @@ + + + + +Backups + + + + + + + + next up previous contents index
+ Next: On the importance of +Up: Linux System Administrators' Guide + Previous: Disabling a user temporarily +

+

Backups

+   +

+

+ + Hardware is indeterministically reliable.
+ Software is deterministically unreliable.
+ People are indeterministically unreliable.
+ Nature is deterministically reliable.
+

+

+ This chapter explains about why, how, and when to make + backups, and how to restore things from backups. +

+

+ +
+

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node97.html b/sag-0.6.1-www/Invisible/sag-0.6/node97.html new file mode 100644 index 0000000..2f1ca72 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node97.html @@ -0,0 +1,71 @@ + + + + +On the importance of being backed up + + + + + + + + next up previous contents index
+ Next: Selecting the backup medium +Up: Backups + Previous: Backups +

+

On the importance of being backed up

+

+ Your data is valuable. It will cost you time and effort re-create + it, and that costs money or at least personal grief and tears; + sometimes it can't even be re-created, e.g., if it is the + results of some experiments. Since it is an investment, you + should protect it and take steps to avoid losing it. +

+ There are basically four reasons why you might lose data: hardware + failures, software bugs, human action, or natural + disasters.gif + Although modern hardware tends to be quite reliable, it can + still break seemingly spontaneously. The most critical piece + of hardware for storing data is the hard disk, which relies on + tiny magnetic fields remaining intact in a world filled with + electromagnetic noise. Modern software doesn't even tend to + be reliable; a rock solid program is an exception, not a rule. + Humans are quite unreliable, they will either make a mistake, + or they will be malicious and destroy data on purpose. Nature + might not be evil, but it can wreak havoc even when being good. + All in all, it is a small miracle that anything works at all. +

+ Backups are a way to protect the investment in data. By having + several copies of the data, it does not matter as much if one + is destroyed (the cost is only that of the restoration of the + lost data from the backup). +

+ It is important to do backups properly. Like everything + else that is related to the physical world, backups will fail + sooner or later. Part of doing backups well is to make sure + they work; you don't want to notice that your backups didn't + work.gif + Adding insult to injury, you might have a bad crash just as + you're making the backup; if you have only one backup medium, + it might destroyed as well, leaving you with the smoking ashes + of hard work.gif Or you + might notice, when trying to restore, that you forgot to back + up something important, like the user database on a 15 000 user + site. Best of all, all your backups might be working perfectly, + but the last known tape drive reading the kind of tapes you + used was the one that now has a bucketful of water in it. +

+ When it comes to backups, paranoia is in the job description. +

+

next up previous contents index
+ Next: Selecting the backup medium +Up: Backups + Previous: Backups +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node98.html b/sag-0.6.1-www/Invisible/sag-0.6/node98.html new file mode 100644 index 0000000..0fa02fb --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node98.html @@ -0,0 +1,76 @@ + + + + +Selecting the backup medium + + + + + + + + next up previous contents index
+ Next: Selecting the backup tool +Up: Backups + Previous: On the importance of +

+

Selecting the backup medium

+

+ The most important decision regarding backups is the choice of + backup medium. You need to consider cost, reliability, speed, + availability, and usability. +

+ Cost is important, since you should preferably have several + times more backup storage than what you need for the data. + A cheap medium is usually a must. +

+ Reliability is extremely + important, since a broken backup can make a grown man cry. + A backup medium must be able to hold data without corruption for + years. + The way you use the medium affects it reliability as a backup + medium. A hard disk is typically very reliable, but as a backup + medium it is not very reliable, if it is in the same computer as + the disk you are backing up. +

+ Speed is usually not very important, if backups can be done + without interaction. It doesn't matter if a backup takes two + hours, as long as it needs no supervision. On the other hand, + if the backup can't be done when the computer would otherwise + be idle, then speed is an issue. +

+ Availability is obviously necessary, since you can't use a backup + medium if it doesn't exist. Less obvious is the need for the + medium to be available even in the future, and on computers other + than your own. Otherwise you may not be able to restore your + backups after a disaster. +

+ Usability is a large factor in how often backups are made. + The easier it is to make backups, the better. A backup medium + mustn't be hard or boring to use. +

+ The typical alternatives are floppies and tapes. Floppies + are very cheap, fairly reliable, not very fast, very available, + but not very usable for large amounts of data. Tapes are + cheap to somewhat expensive, fairly reliable, fairly fast, + quite available, and--depending on the size of the tape--quite + comfortable. +

+ There are other alternatives. They are usually not very good + on availability, but if that is not a problem, they can be + better in other ways. For example, magneto-optical disks can have + good sides of both floppies (they're random access, making + restoration of a single file quick) and tapes (contain a lot + of data). +

+

next up previous contents index
+ Next: Selecting the backup tool +Up: Backups + Previous: On the importance of +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node99.html b/sag-0.6.1-www/Invisible/sag-0.6/node99.html new file mode 100644 index 0000000..03c11d6 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node99.html @@ -0,0 +1,71 @@ + + + + +Selecting the backup tool + + + + + + + + next up previous contents index
+ Next: Simple backups +Up: Backups + Previous: Selecting the backup medium +

+

Selecting the backup tool

+

+ There are many tools that can be used to make backups. The + traditional UNIX tools used for backups are tar , + cpio , and dump . In addition, there are + large number of third party packages (both freeware and + commercial) that can be used. The choice of backup medium + can affect the choice of tool. +

+ tar  and cpio  are similar, and mostly equivalent + from a backup point of view. Both are capable of storing + files on tapes, and retrieving files from them. Both are + capable of using almost any media, since the kernel device + drivers take care of the low level device handling and the + devices all tend to look alike to user level programs. + Some UNIX versions of tar  and cpio  may have + problems with unusual files (symbolic links, device files, + files with very long pathnames, and so on), but the Linux + versions should handle all files correctly. +

+ dump  is different in that it reads the filesystem + directly and not via the filesystem. It is also written + specifically for backups; tar  and cpio  are + really for archiving files, although they work for backups + as well. +

+ Reading the filesystem directly has some advantages. It makes + it possible to back files up without affecting their time + stamps; for tar  and cpio , you would have to mount + the filesystem read-only first. Directly reading the filesystem + is also more effective, if everything needs to be backed up, + since it can be done with much less disk head movement. The + major disadvantage is that it makes the backup program specific + to one filesystem type; the Linux dump  program understands + the ext2 filesystem only. +

+ dump  also directly supports backup levels (which we'll + be discussing below); with tar  and cpio  this has + to be implemented with other tools. +

+ A comparison of the third party backup tools is beyond the + scope of this book. The Linux Software Map lists many of the + freeware ones. +

+

next up previous contents index
+ Next: Simple backups +Up: Backups + Previous: Selecting the backup medium +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/orangeball.gif b/sag-0.6.1-www/Invisible/sag-0.6/orangeball.gif new file mode 100644 index 0000000..e757cd0 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/orangeball.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/pinkball.gif b/sag-0.6.1-www/Invisible/sag-0.6/pinkball.gif new file mode 100644 index 0000000..43e843b Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/pinkball.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/previous_group_motif.gif b/sag-0.6.1-www/Invisible/sag-0.6/previous_group_motif.gif new file mode 100644 index 0000000..03ea0dc Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/previous_group_motif.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/previous_group_motif_gr.gif b/sag-0.6.1-www/Invisible/sag-0.6/previous_group_motif_gr.gif new file mode 100644 index 0000000..c7a1e2b Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/previous_group_motif_gr.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/previous_motif.gif b/sag-0.6.1-www/Invisible/sag-0.6/previous_motif.gif new file mode 100644 index 0000000..aef90f1 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/previous_motif.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/previous_motif_gr.gif b/sag-0.6.1-www/Invisible/sag-0.6/previous_motif_gr.gif new file mode 100644 index 0000000..c6acaab Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/previous_motif_gr.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/purpleball.gif b/sag-0.6.1-www/Invisible/sag-0.6/purpleball.gif new file mode 100644 index 0000000..4836265 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/purpleball.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/redball.gif b/sag-0.6.1-www/Invisible/sag-0.6/redball.gif new file mode 100644 index 0000000..b1a9580 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/redball.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/sag.css b/sag-0.6.1-www/Invisible/sag-0.6/sag.css new file mode 100644 index 0000000..3970428 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/sag.css @@ -0,0 +1,10 @@ + +SMALL.TINY { font-size : xx-small } +SMALL.SCRIPTSIZE { font-size : xx-small } +SMALL.FOOTNOTESIZE { font-size : x-small } +SMALL.SMALL { font-size : small } +BIG.LARGE { font-size : large } +BIG.XLARGE { font-size : x-large } +BIG.XXLARGE { font-size : xx-large } +BIG.HUGE { font-size : xx-large } +BIG.XHUGE { font-size : xx-large } diff --git a/sag-0.6.1-www/Invisible/sag-0.6/sag.html b/sag-0.6.1-www/Invisible/sag-0.6/sag.html new file mode 100644 index 0000000..d39d103 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/sag.html @@ -0,0 +1,76 @@ + + + + + +Linux System Administrators' Guide 0.6 + + + + + + + + + +

Linux System Administrators' Guide 0.6

+ +

Lars Wirzenius + +

[Linux logo] +The Linux Documentation Project + +

This is version 0.6 of the Linux System Administrators' Guide.
+Published November 15, 1997. + +

+ +Contents + +
+ +

The LaTeX source code and other machine readable formats +can be found on the Internet via anonymous ftp on +sunsite.unc.edu, +in the directory /pub/Linux/docs/LDP. +Also available are at least Postscript and TeX .DVI formats. +The official home page for the book is +\texttt{http://www.iki.fi/liw/linux/sag/}. The current version can always +be found at that location. + +

Copyright © 1993-1997 Lars Wirzenius. + +

Trademarks are owned by their owners. + +

Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +

Permission is granted to process the document source code +through TeX or other formatters and print the +results, and distribute the printed document, +provided the printed document carries copying permission +notice identical to this one, including the references to where +the source code can be found and the official home page. + +

Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided that the entire +resulting derived work is distributed under the terms of a permission +notice identical to this one. + +

Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions. + +

The author would appreciate a notification of modifications, translations, +and printed versions. Thank you. + +

+

+ +

This page is dedicated to a future dedication. + +

In the mean time...I'd like someone who knows him let Terry +Pratchett know that his way of using footnotes is rather inspiring. + + + diff --git a/sag-0.6.1-www/Invisible/sag-0.6/up_motif.gif b/sag-0.6.1-www/Invisible/sag-0.6/up_motif.gif new file mode 100644 index 0000000..3d1aebf Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/up_motif.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/up_motif_gr.gif b/sag-0.6.1-www/Invisible/sag-0.6/up_motif_gr.gif new file mode 100644 index 0000000..a8b463a Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/up_motif_gr.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/whiteball.gif b/sag-0.6.1-www/Invisible/sag-0.6/whiteball.gif new file mode 100644 index 0000000..4a90ea1 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/whiteball.gif differ diff --git a/sag-0.6.1-www/Invisible/sag-0.6/yellowball.gif b/sag-0.6.1-www/Invisible/sag-0.6/yellowball.gif new file mode 100644 index 0000000..c6ba6b1 Binary files /dev/null and b/sag-0.6.1-www/Invisible/sag-0.6/yellowball.gif differ diff --git a/sag-0.6.1-www/index.html b/sag-0.6.1-www/index.html new file mode 100644 index 0000000..8a72a1b --- /dev/null +++ b/sag-0.6.1-www/index.html @@ -0,0 +1,49 @@ + + +The Linux System Administrators' Guide + + + +

Note: the LDP home page +is probably much faster, if you are from the US (or otherwise far from +Finland). + +

The Linux System Administrators' Guide

+ +

The Linux System Administrators' Guide (SAG) is targeted at novice +Linux system administrators. It is written by Lars Wirzenius, and +may be copied freely, even commercially. See the book for more +information about copying. + +

The current version is 0.6.1. It was released on 8 February 1999. +(Some of the formats below were released later.) + +

+ +

There is no official plain text version. Yet. + +

Please note that I will not send copies of the SAG via e-mail, or +via any other method. + + + +

Translations

+ +

There are several translations of the SAG available, but I haven't +been keeping track of them. I will do better in the future, and this +page will have a list of the translations I know about. Thus: If you +have a translation of the SAG, please send me the URL. Thanks. + +

(24 March 1999, +Lars Wirzenius) + + + diff --git a/sag-0.6.1-www/sag-0.6.1.html/backup-timeline.gif b/sag-0.6.1-www/sag-0.6.1.html/backup-timeline.gif new file mode 100644 index 0000000..ba477dc Binary files /dev/null and b/sag-0.6.1-www/sag-0.6.1.html/backup-timeline.gif differ diff --git a/sag-0.6.1-www/sag-0.6.1.html/book1.html b/sag-0.6.1-www/sag-0.6.1.html/book1.html new file mode 100644 index 0000000..1b3b4d6 --- /dev/null +++ b/sag-0.6.1-www/sag-0.6.1.html/book1.html @@ -0,0 +1,833 @@ + +The Linux System Administrators' Guide

The Linux System Administrators' Guide

Version 0.6.1

Lars Wirzenius

<liw@iki.fi>
+

An introduction to system administration of a Linux + system for novices.

Copyright 1993--1998 Lars Wirzenius.

Trademarks are owned by their owners.

Permission is granted to make and distribute verbatim + copies of this manual provided the copyright notice and this + permission notice are preserved on all copies.

Permission is granted to process the document source + code through TeX or other formatters and print the results, + and distribute the printed document, provided the printed + document carries copying permission notice identical to this one, + including the references to where the source code can be found + and the official home page.

Permission is granted to copy and distribute modified + versions of this manual under the conditions for verbatim + copying, provided that the entire resulting derived work is + distributed under the terms of a permission notice identical to + this one.

Permission is granted to copy and distribute translations + of this manual into another language, under the above conditions + for modified versions.

The author would appreciate a notification of modifications, + translations, and printed versions. Thank you.

Table of Contents
Dedication
Source and pre-formatted versions available
1. Introduction
The Linux Documentation Project
2. Overview of a Linux System
Various parts of an operating system
Important parts of the kernel
Major services in a UNIX system
init
Logins from terminals
Syslog
Periodic command execution: cron and +at
Graphical user interface
Networking
Network logins
Network file systems
Mail
Printing
The filesystem layout
3. Overview of the Directory Tree
Background
The root filesystem
The /etc directory
The /dev directory
The /usr filesystem
The /var filesystem
The /proc filesystem
4. Using Disks and Other Storage Media
Two kinds of devices
Hard disks
Floppies
CD-ROM's
Tapes
Formatting
Partitions
The MBR, boot sectors and partition table
Extended and logical partitions
Partition types
Partitioning a hard disk
Device files and partitions
Filesystems
What are filesystems?
Filesystems galore
Which filesystem should be used?
Creating a filesystem
Mounting and unmounting
Checking filesystem integrity with fsck
Checking for disk errors with badblocks
Fighting fragmentation
Other tools for all filesystems
Other tools for the ext2 filesystem
Disks without filesystems
Allocating disk space
Partitioning schemes
Space requirements
Examples of hard disk allocation
Adding more disk space for Linux
Tips for saving disk space
5. Memory Management
What is virtual memory?
Creating a swap space
Using a swap space
Sharing swap spaces with other operating systems
Allocating swap space
The buffer cache
6. Boots And Shutdowns
An overview of boots and shutdowns
The boot process in closer look
More about shutdowns
Rebooting
Single user mode
Emergency boot floppies
7. init
init comes first
Configuring init to start getty: the /etc/inittab file
Run levels
Special configuration in /etc/inittab
Booting in single user mode
8. Logging In And Out
Logins via terminals
Logins via the network
What login does
X and xdm
Access control
Shell startup
9. Managing user accounts
What's an account?
Creating a user
/etc/passwd and other informative files
Picking numeric user and group ids
Initial environment: /etc/skel
Creating a user by hand
Changing user properties
Removing a user
Disabling a user temporarily
10. Backups
On the importance of being backed up
Selecting the backup medium
Selecting the backup tool
Simple backups
Making backups with tar
Restoring files with tar
Multilevel backups
What to back up
Compressed backups
11. Keeping Time
Time zones
The hardware and software clocks
Showing and setting time
When the clock is wrong
Glossary (DRAFT)
  Next
  Dedication
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The Linux System Administrators' Guide
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Chapter 5. Memory Management

Table of Contents
What is virtual memory?
Creating a swap space
Using a swap space
Sharing swap spaces with other operating systems
Allocating swap space
The buffer cache

“Minnet, jag har tappat mitt minne, + är jag svensk eller finne, kommer inte ihåg...” + (Bosse Österberg) +

This section describes the Linux memory management + features, i.e., virtual memory and the disk buffer cache. + The purpose and workings and the things the system administrator + needs to take into consideration are described.

What is virtual memory?

Linux supports virtual memory, that + is, using a disk as an extension of RAM so that the effective + size of usable memory grows correspondingly. The kernel will + write the contents of a currently unused block of memory to the + hard disk so that the memory can be used for another purpose. + When the original contents are needed again, they are read back + into memory. This is all made completely transparent to the + user; programs running under Linux only see the larger amount of + memory available and don't notice that parts of them reside on + the disk from time to time. Of course, reading and writing the + hard disk is slower (on the order of a thousand times slower) + than using real memory, so the programs don't run as fast. + The part of the hard disk that is used as virtual memory is + called the swap space.

Linux can use either a normal file in the filesystem or a + separate partition for swap space. A swap partition is + faster, but it is easier to change the size of a swap file + (there's no need to repartition the whole hard disk, and + possibly install everything from scratch). When you know how + much swap space you need, you should go for a swap partition, + but if you are uncertain, you can use a swap file first, use + the system for a while so that you can get a feel for how much + swap you need, and then make a swap partition when you're + confident about its size.

You should also know that Linux allows one to use several swap + partitions and/or swap files at the same time. This means + that if you only occasionally need an unusual amount of swap space, + you can set up an extra swap file at such times, instead of + keeping the whole amount allocated all the time.

A note on operating system terminology: computer science usually + distinguishes between swapping (writing the whole process out to + swap space) and paging (writing only fixed size parts, usually + a few kilobytes, at a time). Paging is usually more efficient, + and that's what Linux does, but traditional Linux terminology + talks about swapping anyway. + + [1] +

Notes

[1]

Thus quite needlessly annoying a + number of computer scientists something horrible. +

PrevHomeNext
Allocating disk space Creating a swap space
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The Linux System Administrators' Guide
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Chapter 6. Boots And Shutdowns

Table of Contents
An overview of boots and shutdowns
The boot process in closer look
More about shutdowns
Rebooting
Single user mode
Emergency boot floppies

Start me up
+Ah... you've got to... you've got to
+Never, never never stop
+Start it up
+Ah... start it up, never, never, never
+ You make a grown man cry,
+  you make a grown man cry
+(Rolling Stones)

This section explains what goes on when a Linux system is + brought up and taken down, and how it should be done properly. + If proper procedures are not followed, files might be corrupted + or lost.

An overview of boots and shutdowns

The act of turning on a computer system and causing its + operating system to be loaded + + [1] + + is called booting. The name comes from + an image of the computer pulling itself up from its bootstraps, + but the act itself slightly more realistic.

During bootstrapping, the computer first loads a small piece + of code called the bootstrap loader, which + in turn loads and starts the operating system. The bootstrap + loader is usually stored in a fixed location on a hard disk + or a floppy. The reason for this two step process is that + the operating system is big and complicated, but the first + piece of code that the computer loads must be very small (a + few hundred bytes), to avoid making the firmware unnecessarily + complicated.

Different computers do the bootstrapping differently. + For PC's, the computer (its BIOS) reads in the first sector + (called the boot sector) of a floppy or + hard disk. The bootstrap loader is contained within this sector. + It loads the operating system from elsewhere on the disk (or + from some other place).

After Linux has been loaded, it initializes the hardware and + device drivers, and then runs init. init + starts other processes to allow users to log in, and do things. + The details of this part will be discussed below.

In order to shut down a Linux system, first all processes + are told to terminate (this makes them close any files and + do other necessary things to keep things tidy), then filesystems + and swap areas are unmounted, and finally a message is printed + to the console that the power can be turned off. If the proper + procedure is not followed, terrible things can and will happen; + most importantly, the filesystem buffer cache might not be flushed, + which means that all data in it is lost and the filesystem on + disk is inconsistent, and therefore possibly unusable. +

Notes

[1]

On early computers, it wasn't enough + to merely turn on the computer, you had to manually load the + operating system as well. These new-fangled thing-a-ma-jigs do + it all by themselves.

PrevHomeNext
The buffer cache The boot process in closer look
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The Linux System Administrators' Guide
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Chapter 7. init

Table of Contents
init comes first
Configuring init to start getty: the /etc/inittab file
Run levels
Special configuration in /etc/inittab
Booting in single user mode

“Uuno on numero yksi” + (Slogan for a series of Finnish movies.)

+ +

This chapter describes the init process, + which is the first user level process started by the kernel. + init has many important duties, such as + starting getty (so that users can log in), + implementing run levels, and taking care of orphaned processes. + This chapter explains how init is configured + and how you can make use of the different run levels.

init comes first

init is one of those programs that + are absolutely essential to the operation of a Linux system, + but that you still can mostly ignore. A good Linux distribution + will come with a configuration for init + that will work for most systems, and on these systems there is + nothing you need to do about init. Usually, + you only need to worry about init if you hook + up serial terminals, dial-in (not dial-out) modems, or if you + want to change the default run level.

When the kernel has started itself (has been loaded + into memory, has started running, and has initialized all + device drivers and data structures and such), it finishes its + own part of the boot process by starting a user level program, + init. Thus, init is always + the first process (its process number is always 1).

The kernel looks for init + in a few locations that have been historically used + for it, but the proper location for it (on a Linux + system) is /sbin/init. If the + kernel can't find init, it tries to run + /bin/sh, and if that also fails, the startup + of the system fails.

When init starts, it finishes the + boot process by doing a number of administrative tasks, such + as checking filesystems, cleaning up /tmp, + starting various services, and starting a getty + for each terminal and virtual console where users should be able + to log in (see Chapter 8).

After the system is properly up, init + restarts getty for each terminal + after a user has logged out (so that the next user can log + in). init also adopts orphan processes: when + a process starts a child process and dies before its child, the + child immediately becomes a child of init. + This is important for various technical reasons, but it is good + to know it, since it makes it easier to understand process lists + and process tree graphs. + + [1] + + There are a few variants of init + available. Most Linux distributions + use sysvinit (written by Miquel + van Smoorenburg), which is based on the System V + init design. The BSD versions of Unix have + a different init. The primary difference + is run levels: System V has them, BSD does not (at least + traditionally). This difference is not essential. We'll look + at sysvinit only.

Notes

[1]

init itself is not + allowed to die. You can't kill init + even with SIGKILL.

PrevHomeNext
Emergency boot floppies Configuring init to start getty: the /etc/inittab file
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The Linux System Administrators' Guide
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Chapter 8. Logging In And Out

Table of Contents
Logins via terminals
Logins via the network
What login does
X and xdm
Access control
Shell startup

“I don't care to belong to a club + that accepts people like me as a member.” + (Groucho Marx)

This section describes what happens when a user logs + in or out. The various interactions of background processes, + log files, configuration files, and so on are described in + some detail. +

Logins via terminals

Figure 8-1 shows how logins happen via + terminals. First, init makes sure there is + a getty program for the terminal connection + (or console). getty listens at the terminal + and waits for the user to notify that he is ready to login in + (this usually means that the user must type something). When it + notices a user, getty outputs a welcome message + (stored in /etc/issue), and prompts for + the username, and finally runs the login + program. login gets the username as a + parameter, and prompts the user for the password. If these + match, login starts the shell configured + for the user; else it just exits and terminates the process + (perhaps after giving the user another chance at entering the + username and password). init notices that + the process terminated, and starts a new getty + for the terminal. +

Figure 8-1. Logins via terminals: the interaction of init, getty, login, and the shell.

Note that the only new process is the + one created by init (using the + fork system call); getty + and login only replace the program running in + the process (using the exec system call). +

A separate program, for noticing the user, is needed + for serial lines, since it can be (and traditionally was) + complicated to notice when a terminal becomes active. + getty also adapts to the speed and other + settings of the connection, which is important especially for + dial-in connections, where these parameters may change from call + to call.

There are several versions of getty + and init in use, all with their good and + bad points. It is a good idea to learn about the versions on + your system, and also about the other versions (you could use the + Linux Software Map to search them). If you don't have dial-in's, + you probably don't have to worry about getty, + but init is still important.

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Booting in single user mode Logins via the network
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The Linux System Administrators' Guide
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Chapter 9. Managing user accounts

Table of Contents
What's an account?
Creating a user
Changing user properties
Removing a user
Disabling a user temporarily

“The similarities of sysadmins and drug + dealers: both measure stuff in K's, and both have users.” + (Old, tired computer joke.)

This chapter explains how to create new user accounts, + how to modify the properties of those accounts, and how to remove + the accounts. Different Linux systems have different tools for + doing this.

What's an account?

When a computer is used by many people it is usually + necessary to differentiate between the users, for example, so that + their private files can be kept private. This is important even + if the computer can only be used by a single person at a time, + as with most microcomputers. + + [1] + + Thus, each user is given a unique username, and that name is + used to log in.

There's more to a user than just a name, however. An + account is all the files, resources, + and information belonging to one user. The term hints at banks, + and in a commercial system each account usually has some money + attached to it, and that money vanishes at different speeds + depending on how much the user stresses the system. For example, + disk space might have a price per megabyte and day, and processing + time might have a price per second.

Notes

[1]

It might be quite embarrassing if my + sister could read my love letters.

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Shell startup Creating a user
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Chapter 3. Overview of the Directory Tree

Table of Contents
Background
The root filesystem
The /etc directory
The /dev directory
The /usr filesystem
The /var filesystem
The /proc filesystem

“ Two days later, there was Pooh, sitting + on his branch, dangling his legs, and there, beside him, were + four pots of honey...” (A.A.\ Milne)

This chapter describes the important parts of a standard + Linux directory tree, based on the FSSTND filesystem + standard. It outlines the normal way of breaking the directory + tree into separate filesystems with different purposes and gives + the motivation behind this particular split. Some alternative + ways of splitting are also described.

Background

This chapter is loosely based on the Linux + filesystem standard, FSSTND, version 1.2 (see + the bibliography), which attempts to set a standard for how + the directory tree in a Linux system is organized. Such a + standard has the advantage that it will be easier to write or + port software for Linux, and to administer Linux machines, since + everything will be in their usual places. There is no authority + behind the standard that forces anyone to comply with it, but it + has got the support of most, if not all, Linux distributions. + It is not a good idea to break with the FSSTND without very + compelling reasons. The FSSTND attempts to follow Unix tradition + and current trends, making Linux systems familiar to those with + experience with other Unix systems, and vice versa.

This chapter is not as detailed as the FSSTND. A system + administrator should also read the FSSTND for a complete + understanding.

This chapter does not explain all files in detail. + The intention is not to describe every file, but to give + an overview of the system from a filesystem point of view. + Further information on each file is available elsewhere in this + manual or the manual pages.

The full directory tree is intended to be breakable + into smaller parts, each on its own disk or partition, + to accomodate to disk size limits and to ease backup + and other system administration. The major parts are the + root, /usr, /var, and + /home filesystems (see + Figure 3-1). Each part has a different purpose. + The directory tree has been designed so that it works well in + a network of Linux machines which may share some parts of the + filesystems over a read-only device (e.g., a CD-ROM), or over + the network with NFS.

Figure 3-1. Parts of a Unix directory tree. Dashed lines indicate partition limits.

The roles of the different parts of the directory tree are + described below. + +

  • The root filesystem is specific for + each machine (it is generally stored on a local disk, + although it could be a ramdisk or network drive as well) + and contains the files that are necessary for booting + the system up, and to bring it up to such a state that + the other filesystems may be mounted. The contents of + the root filesystem will therefore be sufficient for + the single user state. It will also contain tools for + fixing a broken system, and for recovering lost files + from backups.

  • The /usr filesystem + contains all commands, libraries, manual pages, and + other unchanging files needed during normal operation. + No files in /usr should be specific + for any given machine, nor should they be modified during + normal use. This allows the files to be shared over + the network, which can be cost-effective since it saves + disk space (there can easily be hundreds of megabytes in + /usr), and can make administration + easier (only the master /usr needs to + be changed when updating an application, not each machine + separately). Even if the filesystem is on a local disk, + it could be mounted read-only, to lessen the chance of + filesystem corruption during a crash.

  • The /var + filesystem contains files that change, such as spool + directories (for mail, news, printers, etc), log + files, formatted manual pages, and temporary files. + Traditionally everything in /var + has been somewhere below /usr, but + that made it impossible to mount /usr + read-only.

  • The /home + filesystem contains the users' home directories, i.e., all + the real data on the system. Separating home directories + to their own directory tree or filesystem makes backups + easier; the other parts often do not have to be backed + up, or at least not as often (they seldom change). + A big /home might have to be + broken on several filesystems, which requires adding an + extra naming level below /home, + e.g., /home/students and + /home/staff.

Although the different parts have been called filesystems + above, there is no requirement that they actually be on separate + filesystems. They could easily be kept in a single one if the + system is a small single-user system and the user wants to keep + things simple. The directory tree might also be divided into + filesystems differently, depending on how large the disks are, and + how space is allocated for various purposes. The important part, + though, is that all the standard names + work; even if, say, /var and + /usr are actually on the same + partition, the names /usr/lib/libc.a + and /var/log/messages must work, for + example by moving files below /var + into /usr/var, and + making /var a symlink to + /usr/var.

The Unix filesystem structure groups files according to purpose, + i.e., all commands are in one place, all data files in another, + documentation in a third, and so on. An alternative would be to + group files files according to the program they belong to, i.e., + all Emacs files would be in one directory, all TeX in another, + and so on. The problem with the latter approach is that it + makes it difficult to share files (the program directory often + contains both static and shareable and changing and + non-shareable files), and sometimes to even find the files + (e.g., manual pages in a huge number of places, and making the + manual page programs find all of them is a maintenance + nightmare).

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Major services in a UNIX system The root filesystem
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Chapter 10. Backups

Table of Contents
On the importance of being backed up
Selecting the backup medium
Selecting the backup tool
Simple backups
Multilevel backups
What to back up
Compressed backups

Hardware is indeterministically reliable. 
+Software is deterministically unreliable.
+People are indeterministically unreliable.
+Nature is deterministically reliable.

This chapter explains about why, how, and when to make + backups, and how to restore things from backups.

On the importance of being backed up

Your data is valuable. It will cost you time and effort + re-create it, and that costs money or at least personal grief + and tears; sometimes it can't even be re-created, e.g., if it + is the results of some experiments. Since it is an investment, + you should protect it and take steps to avoid losing it.

There are basically four reasons why you might lose data: + hardware failures, software bugs, human action, or natural + disasters. + + [1] + + Although modern hardware tends to be quite reliable, it can + still break seemingly spontaneously. The most critical piece + of hardware for storing data is the hard disk, which relies on + tiny magnetic fields remaining intact in a world filled with + electromagnetic noise. Modern software doesn't even tend to + be reliable; a rock solid program is an exception, not a rule. + Humans are quite unreliable, they will either make a mistake, or + they will be malicious and destroy data on purpose. Nature might + not be evil, but it can wreak havoc even when being good. All in + all, it is a small miracle that anything works at all.

Backups are a way to protect the investment in data. + By having several copies of the data, it does not matter as much + if one is destroyed (the cost is only that of the restoration + of the lost data from the backup).

It is important to do backups properly. Like everything + else that is related to the physical world, backups will fail + sooner or later. Part of doing backups well is to make sure + they work; you don't want to notice that your backups didn't work. + + [2] + + Adding insult to injury, you might have a bad crash just as + you're making the backup; if you have only one backup medium, + it might destroyed as well, leaving you with the smoking ashes + of hard work. + + [3] + + Or you might notice, when trying to restore, that you forgot to + back up something important, like the user database on a 15000 + user site. Best of all, all your backups might be working + perfectly, but the last known tape drive reading the kind of + tapes you used was the one that now has a bucketful of water + in it.

When it comes to backups, paranoia is in the job + description.

Notes

[1]

The fifth reason is ``something + else''.

[2]

Don't laugh. This has happened to + several people.

[3]

Been there, done that...

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Disabling a user temporarily Selecting the backup medium
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Chapter 11. Keeping Time

Table of Contents
Time zones
The hardware and software clocks
Showing and setting time
When the clock is wrong

“Time is an illusion. Lunchtime double + so.” (Douglas Adams.)

This chapter explains how a Linux system keeps time, + and what you need to do to avoid causing trouble. Usually, + you don't need to do anything about time, but it is good to + understand it.

Time zones

Time measurement is based on mostly regular natural + phenomena, such as alternating light and dark periods caused + by the rotation of the planet. The total time taken by two + successive periods is constant, but the lengths of the light + and dark period vary. One simple constant is noon.

Noon is the time of the day when the Sun is at its + highest position. Since the Earth is round, + + [1] + + noon happens at different times in different places. This leads + to the concept of local time. Humans + measure time in many units, most of which are tied to natural + phenomena like noon. As long as you stay in the same place, + it doesn't matter that local times differ.

As soon as you need to communicate with distant places, + you'll notice the need for a common time. In modern times, + most of the places in the world communicate with most other + places in the world, so a global standard for measuring time + has been defined. This time is called universal + time (UT or UTC, formerly known as Greenwich Mean Time + or GMT, since it used to be local time in Greenwich, England). + When people with different local times need to communicate, + they can express times in universal time, so that there is no + confusion about when things should happen.

Each local time is called a time zone. While geography + would allow all places that have noon at the same time have the + same time zone, politics makes it difficult. For various reasons, + many countries use daylight savings time, + that is, they move their clocks to have more natural light + while they work, and then move the clocks back during winter. + Other countries do not do this. Those that do, do not agree when + the clocks should be moved, and they change the rules from year + to year. This makes time zone conversions definitely non-trivial. +

Time zones are best named by the location or by telling + the difference between local and universal time. In the US + and some other countries, the local time zones have a name and + a three letter abbreviation. The abbreviations are not unique, + however, and should not be used unless the country is also named. + It is better to talk about the local time in, say, Helsinki, + than about East European time, since not all countries in Eastern + Europe follow the same rules.

Linux has a time zone package that knows about all + existing time zones, and that can easily be updated when the + rules change. All the system administrator needs to do is to + select the appropriate time zone. Also, each user can set his + own time zone; this is important since many people work with + computers in different countries over the Internet. When the + rules for daylight savings time change in your local time zone, + make sure you'll upgrade at least that part of your Linux system. + Other than setting the system time zone and upgrading the time + zone data files, there is little need to bother about time. +

Notes

[1]

According to + recent research.

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Compressed backups The hardware and software clocks
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Chapter 1. Introduction

“In the beginning, the file was without + form, and void; and emptiness was upon the face of the bits. + And the Fingers of the Author moved upon the face of the + keyboard. And the Author said, Let there be words, and there + were words.”

This manual, the Linux System Administrators' Guide, + describes the system administration aspects of using Linux. + It is intended for people who know next to nothing about system + administration (as in ``what is it?''), but who have already + mastered at least the basics of normal usage. This manual also + doesn't tell you how to install Linux; that is described in the + Installation and Getting Started document. See below for more + information about Linux manuals.

System administration is all the things that one has to + do to keep a computer system in a useable shape. It includes + things like backing up files (and restoring them if necessary), + installing new programs, creating accounts for users (and deleting + them when no longer needed), making certain that the filesystem + is not corrupted, and so on. If a computer were, say, a house, + system administration would be called maintenance, and would + include cleaning, fixing broken windows, and other such things. + System administration is not called maintenance, because that + would be too simple. + + [1] + +

The structure of this manual is such that many of the + chapters should be usable independently, so that if you need + information about, say, backups, you can read just that chapter. + This hopefully makes the book easier to use as a reference manual, + and makes it possible to read just a small part when needed, + instead of having to read everything. However, this manual is + first and foremost a tutorial, and a reference manual only as + a lucky coincidence.

This manual is not intended to be used completely by itself. + Plenty of the rest of the Linux documentation is also important + for system administrators. After all, a system administrator is + just a user with special privileges and duties. A very important + resource are the manual pages, which should always be consulted + when a command is not familiar.

While this manual is targeted at Linux, a general principle + has been that it should be useful with other UNIX based operating + systems as well. Unfortunately, since there is so much variance + between different versions of UNIX in general, and in system + administration in particular, there is little hope to cover + all variants. Even covering all possibilities for Linux is + difficult, due to the nature of its development.

There is no one official Linux distribution, so different + people have different setups, and many people have a setup they + have built up themselves. This book is not targeted at any + one distribution, even though I use the Debian GNU/Linux system + almost exclusively. When possible, I have tried to point out + differences, and explain several alternatives.

I have tried to describe how things work, rather than just + listing ``five easy steps'' for each task. This means that there + is much information here that is not necessary for everyone, + but those parts are marked as such and can be skipped if you + use a preconfigured system. Reading everything will, naturally, + increase your understanding of the system and should make using + and administering it more pleasant.

Like all other Linux related development, the work was + done on a volunteer basis: I did it because I thought it might + be fun and because I felt it should be done. However, like all + volunteer work, there is a limit to how much effort I have been + able to spend, and also on how much knowledge and experience + I have. This means that the manual is not necessarily as good + as it would be if a wizard had been paid handsomely to write it + and had spent a few years to perfect it. I think, of course, + that it is pretty nice, but be warned.

One particular point where I have cut corners is that I + have not covered very thoroughly many things that are already + well documented in other freely available manuals. This applies + especially to program specific documentation, such as all the + details of using mkfs}. I only describe the + purpose of the program, and as much of its usage as is necessary + for the purposes of this manual. For further information, + I refer the gentle reader to these other manuals. Usually, + all of the referred to documentation is part of the full Linux + documentation set.

While I have tried to make this manual as good as possible, + I would really like to hear from you if you have any ideas on + how to make it better. Bad language, factual errors, ideas for + new areas to cover, rewritten sections, information about how + various UNIX versions do things, I am interested in all of it. My + contact information is available via the World Wide Web at http://www.iki.fi/liw/mail-to-lasu.html. +

Many people have helped me with this book, directly or + indirectly. I would like to especially thank Matt Welsh for + inspiration and LDP leadership, Andy Oram for getting me to work + again with much-valued feedback, Olaf Kirch for showing me that it + can be done, and Adam Richter at Yggdrasil and others for showing + me that other people can find it interesting as well.

Stephen Tweedie, H.~Peter Anvin, R\'emy Card, Theodore + Ts'o, and Stephen Tweedie have let me borrow their work (and + thus make the book look thicker and much more impressive): + a comparison between the xia and ext2 filesystems, the device + list and a description of the ext2 filesystem. These aren't + part of the book any more. I am most grateful for this, and + very apologetic for the earlier versions that sometimes lacked + proper attribution.

In addition, I would like to thank Mark Komarinski for + sending his material in 1993 and the many system administration + columns in Linux Journal. They are quite informative and + inspirational.

Many useful comments have been sent by a large number + of people. My miniature black hole of an archive doesn't let + me find all their names, but some of them are, in alphabetical + order: Paul Caprioli, Ales Cepek, Marie-France Declerfayt, + Dave Dobson, Olaf Flebbe, Helmut Geyer, Larry Greenfield and + his father, Stephen Harris, Jyrki Havia, Jim Haynes, York Lam, + Timothy Andrew Lister, Jim Lynch, Michael J. Micek, Jacob Navia, + Dan Poirier, Daniel Quinlan, Jouni K Seppänen, Philippe Steindl, + G.B.\ Stotte. My apologies to anyone I have forgotten.

META need to add typographical conventsions and LDP blurb + here.

The Linux Documentation Project

The Linux Documentation Project, or LDP, is a loose team + of writers, proofreaders, and editors who are working together + to provide complete documentation for the Linux operating system. + The overall coordinator of the project is Greg Hankins.

This manual is one in a set of several being + distributed by the LDP, including a Linux Users' Guide, + System Administrators' Guide, Network Administrators' Guide, + and Kernel Hackers' Guide. These manuals are all available + in source format, .dvi format, and postscript output + by anonymous FTP from sunsite.unc.edu, in the directory + /pub/Linux/docs/LDP.

We encourage anyone with a penchant for writing or editing + to join us in improving Linux documentation. If you have + Internet e-mail access, you can contact Greg Hankins at + <gregh@sunsite.unc.edu>.

Notes

[1]

There are some people who + do call it that, but that's + just because they have never read this manual, poor + things.

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Source and pre-formatted versions available Overview of a Linux System
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Chapter 2. Overview of a Linux System

Table of Contents
Various parts of an operating system
Important parts of the kernel
Major services in a UNIX system

“God looked over everything he + had made, and saw that it was very good. ” (Genesis + 1:31)

This chapter gives an overview of a Linux system. First, + the major services provided by the operating system are described. + Then, the programs that implement these services are described + with a considerable lack of detail. The purpose of this chapter + is to give an understanding of the system as a whole, so that + each part is described in detail elsewhere.

Various parts of an operating system

A UNIX operating system consists + of a kernel and some + system programs. There are also some + application programs} for doing work. + The kernel is the heart of the operating system. + + [1] + + It keeps track of files on the disk, starts programs and runs + them concurrently, assigns memory and other resources to various + processes, receives packets from and sends packets to the network, + and so on. The kernel does very little by itself, but it provides + tools with which all services can be built. It also prevents + anyone from accessing the hardware directly, forcing everyone + to use the tools it provides. This way the kernel provides + some protection for users from each other. The tools provided + by the kernel are used via system calls; + see manual page section 2 for more information on these.

The system programs use the tools provided by the kernel to + implement the various services required from an operating system. + System programs, and all other programs, run `on top of the + kernel', in what is called the user mode. + The difference between system and application programs is + one of intent: applications are intended for getting useful + things done (or for playing, if it happens to be a game), + whereas system programs are needed to get the system working. + A word processor is an application; telnet + is a system program. The difference is often somewhat blurry, + however, and is important only to compulsive categorizers.

An operating system can also contain compilers and their + corresponding libraries (GCC and the C library in particular under + Linux), although not all programming languages need be part of + the operating system. Documentation, and sometimes even games, + can also be part of it. Traditionally, the operating system has + been defined by the contents of the installation tape or disks; + with Linux it is not as clear since it is spread all over the + FTP sites of the world.

Notes

[1]

In fact, it is often mistakenly considered + to be the operating system itself, but it is not. + An operating system provides many more services than a + plain kernel.

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Introduction Important parts of the kernel
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Chapter 4. Using Disks and Other Storage Media

Table of Contents
Two kinds of devices
Hard disks
Floppies
CD-ROM's
Tapes
Formatting
Partitions
Filesystems
Disks without filesystems
Allocating disk space

“On a clear disk you can seek forever. + ”

When you install or upgrade your system, you need to do a + fair amount of work on your disks. You have to make filesystems + on your disks so that files can be stored on them and reserve + space for the different parts of your system.

This chapter explains all these initial activities. Usually, + once you get your system set up, you won't have to go through + the work again, except for using floppies. You'll need to come + back to this chapter if you add a new disk or want to fine-tune + your disk usage.

The basic tasks in administering disks are: + +

  • Format your disk. This does various things to prepare it for + use, such as checking for bad sectors. (Formatting is nowadays + not necessary for most hard disks.)

  • Partition a hard disk, if you want to use it for several + activities that aren't supposed to interfere with one another. + One reason for partitioning is to store different operating + systems on the same disk. Another reason is to keep user + files separate from system files, which simplifies back-ups + and helps protect the system files from corruption. +

  • Make a filesystem (of a suitable type) on each disk or partition. + The disk means + nothing to Linux until you make a filesystem; then files can + be created and accessed on it. +

  • Mount different filesystems to form a single tree structure, either + automatically, or manually as needed. (Manually mounted filesystems + usually need to be unmounted manually as well.) +

+ +

Chapter 5 contains information + about virtual memory and disk caching, of which you also need + to be aware when using disks.

Two kinds of devices

UNIX, and therefore Linux, recognizes two different + kinds of device: random-access block devices (such as disks), + and character devices (such as tapes and serial lines), + some of which may be serial, and some random-access. Each + supported device is represented in the filesystem as a + device file. + When you read or write a device file, the + data comes from or goes to the device it represents. This way + no special programs (and no special application programming + methodology, such as catching interrupts or polling a serial + port) are necessary to access devices; for example, to send a + file to the printer, one could just say + +

$ cat filename > /dev/lp1
+$
+ + and the contents of the file are printed (the file must, of + course, be in a form that the printer understands). However, + since it is not a good idea to have several people cat their + files to the printer at the same time, one usually uses a special + program to send the files to be printed (usually lpr). + This program makes sure that only one file is being printed + at a time, and will automatically send files to the printer as + soon as it finishes with the previous file. Something similar + is needed for most devices. In fact, one seldom needs to worry + about device files at all.

Since devices show up as files in the filesystem (in the + /dev directory), it is easy + to see just what device files exist, using ls or + another suitable command. In the output of ls -l, the + first column contains the type of the file and its + permissions. For example, inspecting a serial device + gives on my system + +

$ ls -l /dev/cua0
+crw-rw-rw-   1 root     uucp       5,  64 Nov 30  1993 /dev/cua0
+$
+ + The first character in the first column, i.e., + `c' in crw-rw-rw- + above, tells an informed user the type of the file, in this + case a character device. For ordinary files, the first + character is `-', for directories + it is `d', and for block devices + `b'; see the ls man page + for further information.

Note that usually all device files exist even though the + device itself might be not be installed. So just because you + have a file /dev/sda, it doesn't mean that you really do + have an SCSI hard disk. Having all the device files makes the + installation programs simpler, and makes it easier to add new + hardware (there is no need to find out the correct parameters + for and create the device files for the new device).

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The /proc filesystem Hard disks
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Dedication

This place is dedicated to a future dedication.

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The Linux System Administrators' Guide Source and pre-formatted versions available
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Source and pre-formatted versions available

The source code and and other machine readable formats + of this book can be found on the Internet via anonymous + FTP at the Linux Documentation Project home page http://sunsite.unc.edu/LDP/, + or at the home page of this book at http://www.iki.fi/liw/linux/sag/. + Available are at least PostScript and TeX .DVI formats.

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Dedication Introduction
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The Linux System Administrators' Guide
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Glossary (DRAFT)

“The Librarian of the Unseen University + had unilaterally decided to aid comprehension + by producing an Orang-utan/Human Dictionary. + He'd been working on it for three months. + It wasn't easy. He'd got as far as `Oook.'” + (Terry Pratchett, ``Men At Arms'')

This is a short list of word definitions for concepts + relating to Linux and system administration.

ambition

The act of writing funny sentences in the hope of getting them + into the Linux cookie file. +

application program

Software that does something useful. The results of using an + application program is what the computer was bought for. + See also system program, operating system. +

daemon

A process lurking in the background, usually unnoticed, until + something triggers it into action. For example, the \cmd{update} + daemon wakes up every thirty seconds or so to flush the buffer + cache, and the \cmd{sendmail} daemon awakes whenever someone sends + mail. +

file system

The methods and data structures that an operating + system uses to keep track of files on a disk or partition; + the way the files are organized on the disk. Also used about + a partition or disk that is used to store the files + or the type of the filesystem. +

glossary

A list of words and explanations of what they do. Not + to be confused with a dictionary, which is also a list of + words and explanations. +

kernel

Part of an operating system that implements the interaction with + hardware and the sharing of resources. See also system program. +

operating system

Software that shares a computer system's resources (processor, + memory, disk space, network bandwidth, and so on) between + users and the application programs they run. Controls access + to the system to provide security. See also kernel, system program, + application program. +

system call

The services provided by the kernel to application programs, + and the way in which they are invoked. See section 2 of the + manual pages. +

system program

Programs that implement high level functionality of an operating + system, i.e., things that aren't directly dependent on the + hardware. May sometimes require special privileges to run + (e.g., for delivering electronic mail), but often just commonly + thought of as part of the system (e.g., a compiler). See also + application program, kernel, operating system. +

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When the clock is wrong  
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The Linux System Administrators' Guide

Version 0.6.1

Lars Wirzenius

<liw@iki.fi>
+

An introduction to system administration of a Linux + system for novices.

Copyright 1993--1998 Lars Wirzenius.

Trademarks are owned by their owners.

Permission is granted to make and distribute verbatim + copies of this manual provided the copyright notice and this + permission notice are preserved on all copies.

Permission is granted to process the document source + code through TeX or other formatters and print the results, + and distribute the printed document, provided the printed + document carries copying permission notice identical to this one, + including the references to where the source code can be found + and the official home page.

Permission is granted to copy and distribute modified + versions of this manual under the conditions for verbatim + copying, provided that the entire resulting derived work is + distributed under the terms of a permission notice identical to + this one.

Permission is granted to copy and distribute translations + of this manual into another language, under the above conditions + for modified versions.

The author would appreciate a notification of modifications, + translations, and printed versions. Thank you.

Table of Contents
Dedication
Source and pre-formatted versions available
1. Introduction
The Linux Documentation Project
2. Overview of a Linux System
Various parts of an operating system
Important parts of the kernel
Major services in a UNIX system
init
Logins from terminals
Syslog
Periodic command execution: cron and +at
Graphical user interface
Networking
Network logins
Network file systems
Mail
Printing
The filesystem layout
3. Overview of the Directory Tree
Background
The root filesystem
The /etc directory
The /dev directory
The /usr filesystem
The /var filesystem
The /proc filesystem
4. Using Disks and Other Storage Media
Two kinds of devices
Hard disks
Floppies
CD-ROM's
Tapes
Formatting
Partitions
The MBR, boot sectors and partition table
Extended and logical partitions
Partition types
Partitioning a hard disk
Device files and partitions
Filesystems
What are filesystems?
Filesystems galore
Which filesystem should be used?
Creating a filesystem
Mounting and unmounting
Checking filesystem integrity with fsck
Checking for disk errors with badblocks
Fighting fragmentation
Other tools for all filesystems
Other tools for the ext2 filesystem
Disks without filesystems
Allocating disk space
Partitioning schemes
Space requirements
Examples of hard disk allocation
Adding more disk space for Linux
Tips for saving disk space
5. Memory Management
What is virtual memory?
Creating a swap space
Using a swap space
Sharing swap spaces with other operating systems
Allocating swap space
The buffer cache
6. Boots And Shutdowns
An overview of boots and shutdowns
The boot process in closer look
More about shutdowns
Rebooting
Single user mode
Emergency boot floppies
7. init
init comes first
Configuring init to start getty: the /etc/inittab file
Run levels
Special configuration in /etc/inittab
Booting in single user mode
8. Logging In And Out
Logins via terminals
Logins via the network
What login does
X and xdm
Access control
Shell startup
9. Managing user accounts
What's an account?
Creating a user
/etc/passwd and other informative files
Picking numeric user and group ids
Initial environment: /etc/skel
Creating a user by hand
Changing user properties
Removing a user
Disabling a user temporarily
10. Backups
On the importance of being backed up
Selecting the backup medium
Selecting the backup tool
Simple backups
Making backups with tar
Restoring files with tar
Multilevel backups
What to back up
Compressed backups
11. Keeping Time
Time zones
The hardware and software clocks
Showing and setting time
When the clock is wrong
Glossary (DRAFT)
  Next
  Dedication
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The Linux System Administrators' Guide
PrevChapter 4. Using Disks and Other Storage MediaNext

Filesystems

What are filesystems?

A filesystem is the methods and + data structures that an operating system uses to keep track + of files on a disk or partition; that is, the way the files + are organized on the disk. The word is also used to refer to a + partition or disk that is used to store the files or the type of + the filesystem. Thus, one might say ``I have two filesystems'' + meaning one has two partitions on which one stores files, or + that one is using the ``extended filesystem'', meaning the type + of the filesystem.

The difference between a disk or partition and the filesystem + it contains is important. A few programs (including, + reasonably enough, programs that create filesystems) operate + directly on the raw sectors of a disk or partition; if there + is an existing file system there it will be destroyed or + seriously corrupted. Most programs operate on a filesystem, + and therefore won't work on a partition that doesn't contain + one (or that contains one of the wrong type).

Before a partition or disk can be used as a filesystem, it + needs to be initialized, and the bookkeeping data structures need + to be written to the disk. This process is called + making a filesystem.

Most UNIX filesystem types have a similar general + structure, although the exact details vary quite a bit. + The central concepts are superblock, + inode, data block, + directory block, and indirection + block. The superblock contains information + about the filesystem as a whole, such as its size (the exact + information here depends on the filesystem). An inode contains + all information about a file, except its name. The name is + stored in the directory, together with the number of the inode. + A directory entry consists of a filename and the number of + the inode which represents the file. The inode contains the + numbers of several data blocks, which are used to store the + data in the file. There is space only for a few data block + numbers in the inode, however, and if more are needed, more + space for pointers to the data blocks is allocated dynamically. + These dynamically allocated blocks are indirect blocks; the name + indicates that in order to find the data block, one has to find + its number in the indirect block first.

UNIX filesystems usually allow one to create a + hole in a file (this is done with + lseek; check the manual page), which means + that the filesystem just pretends that at a particular place in + the file there is just zero bytes, but no actual disk sectors are + reserved for that place in the file (this means that the file + will use a bit less disk space). This happens especially often + for small binaries, Linux shared libraries, some databases, and + a few other special cases. (Holes are implemented by storing a + special value as the address of the data block in the indirect + block or inode. This special address means that no data block + is allocated for that part of the file, ergo, there is a hole + in the file.)

Holes are moderately useful. On the author's system, + a simple measurement showed a potential for about 4 MB of + savings through holes of about 200 MB total used disk space. + That system, however, contains relatively few programs and no + database files.

Filesystems galore

Linux supports several types of filesystems. As of this + writing the most important ones are: + +

minix

The oldest, presumed to be the most reliable, but quite + limited in features (some time stamps are missing, at + most 30 character filenames) and restricted in + capabilities (at most 64 MB per filesystem). +

xia

A modified version of the minix filesystem that lifts + the limits on the filenames and filesystem sizes, + but does not otherwise introduce new features. It is + not very popular, but is reported to work very well. +

ext2

The most featureful of the native Linux filesystems, + currently also the most popular one. It is designed to + be easily upwards compatible, so that new versions + of the filesystem code do not require re-making the + existing filesystems. +

ext

An older version of ext2 that wasn't upwards + compatible. It is hardly ever used in new installations + any more, and most people have converted to ext2. +

+

In addition, support for several foreign filesystem exists, + to make it easier to exchange files with other operating + systems. These foreign filesystems work just like native + ones, except that they may be lacking in some usual UNIX + features, or have curious limitations, or other oddities. + +

msdos

Compatibility with MS-DOS (and OS/2 and Windows NT) + FAT filesystems. +

usmdos

Extends the msdos filesystem driver under + Linux to get long filenames, owners, + permissions, links, and device files. This allows a normal + msdos filesystem to be used as if it were a + Linux one, thus removing the need for a separate + partition for Linux. +

iso9660

The standard CD-ROM filesystem; the popular Rock Ridge + extension to the CD-ROM standard that allows longer file + names is supported automatically. +

nfs

A networked filesystem that allows sharing a filesystem + between many computers to allow easy access to the + files from all of them. +

hpfs

The OS/2 filesystem. +

sysv

SystemV/386, Coherent, and Xenix filesystems. +

+

The choice of filesystem to use depends on the situation. If + compatibility or other reasons make one of the non-native + filesystems necessary, then that one must be used. If one can + choose freely, then it is probably wisest to use ext2, since + it has all the features but does not suffer from lack of + performance.

There is also the proc filesystem, usually accessible as + the /proc directory, which is not really a + filesystem at all, even though it looks like one. The + proc filesystem makes it easy to access certain kernel + data structures, such as the process list (hence the name). + It makes these + data structures look like a filesystem, and that filesystem + can be manipulated with all the usual file tools. For example, + to get a listing of all processes one might use the + command + +

$ ls -l /proc
+total 0
+dr-xr-xr-x   4 root     root            0 Jan 31 20:37 1
+dr-xr-xr-x   4 liw      users           0 Jan 31 20:37 63
+dr-xr-xr-x   4 liw      users           0 Jan 31 20:37 94
+dr-xr-xr-x   4 liw      users           0 Jan 31 20:37 95
+dr-xr-xr-x   4 root     users           0 Jan 31 20:37 98
+dr-xr-xr-x   4 liw      users           0 Jan 31 20:37 99
+-r--r--r--   1 root     root            0 Jan 31 20:37 devices
+-r--r--r--   1 root     root            0 Jan 31 20:37 dma
+-r--r--r--   1 root     root            0 Jan 31 20:37 filesystems
+-r--r--r--   1 root     root            0 Jan 31 20:37 interrupts
+-r--------   1 root     root      8654848 Jan 31 20:37 kcore
+-r--r--r--   1 root     root            0 Jan 31 11:50 kmsg
+-r--r--r--   1 root     root            0 Jan 31 20:37 ksyms
+-r--r--r--   1 root     root            0 Jan 31 11:51 loadavg
+-r--r--r--   1 root     root            0 Jan 31 20:37 meminfo
+-r--r--r--   1 root     root            0 Jan 31 20:37 modules
+dr-xr-xr-x   2 root     root            0 Jan 31 20:37 net
+dr-xr-xr-x   4 root     root            0 Jan 31 20:37 self
+-r--r--r--   1 root     root            0 Jan 31 20:37 stat
+-r--r--r--   1 root     root            0 Jan 31 20:37 uptime
+-r--r--r--   1 root     root            0 Jan 31 20:37 version
+$
+ + (There will be a few extra files that don't correspond to + processes, though. The above example has been shortened.)

Note that even though it is called a filesystem, no part of + the proc filesystem touches any disk. It exists only in the + kernel's imagination. Whenever anyone tries to look at any + part of the proc filesystem, the kernel makes it look as if + the part existed somewhere, even though it doesn't. So, even + though there is a multi-megabyte /proc/kcore file, + it doesn't take any disk space.

Which filesystem should be used?

There is usually little point in using many different + filesystems. Currently, ext2fs is the most popular one, and + it is probably the wisest choice. Depending on the overhead + for bookkeeping structures, speed, (perceived) reliability, + compatibility, and various other reasons, it may be advisable + to use another file system. This needs to be decided on a + case-by-case basis.

Creating a filesystem

Filesystems are created, i.e., initialized, with the mkfs + command. There is actually a separate program for each filesystem + type. mkfs is just a front end that runs the appropriate + program depending on the desired filesystem type. The type is + selected with the -t fstype option.

The programs called by mkfs have slightly + different command line interfaces. The common and most important + options are summarized below; see the manual pages for more. + +

-t fstype

Select the type of the filesystem. +

-c

Search for bad blocks and initialize the bad + block list accordingly. +

-l filename

Read the initial bad block list from the name file. +

+

To create an ext2 filesystem on a floppy, one would give the + following commands: + +

$ fdformat -n /dev/fd0H1440
+Double-sided, 80 tracks, 18 sec/track. Total capacity 1440 kB.
+Formatting ... done
+$ badblocks /dev/fd0H1440 1440 $>$ bad-blocks
+$ mkfs -t ext2 -l bad-blocks /dev/fd0H1440
+mke2fs 0.5a, 5-Apr-94 for EXT2 FS 0.5, 94/03/10
+360 inodes, 1440 blocks
+72 blocks (5.00%) reserved for the super user
+First data block=1
+Block size=1024 (log=0)
+Fragment size=1024 (log=0)
+1 block group
+8192 blocks per group, 8192 fragments per group
+360 inodes per group
+
+Writing inode tables: done
+Writing superblocks and filesystem accounting information: done
+$
+ + First, the floppy was formatted (the -n option + prevents validation, i.e., bad block checking). Then bad blocks + were searched with badblocks, with the output + redirected to a file, bad-blocks. Finally, + the filesystem was created, with the bad block list initialized + by whatever badblocks found.

The -c option could have been used with + mkfs instead of badblocks + and a separate file. The example below does that. + +

$ mkfs -t ext2 -c /dev/fd0H1440
+mke2fs 0.5a, 5-Apr-94 for EXT2 FS 0.5, 94/03/10
+360 inodes, 1440 blocks
+72 blocks (5.00%) reserved for the super user
+First data block=1
+Block size=1024 (log=0)
+Fragment size=1024 (log=0)
+1 block group
+8192 blocks per group, 8192 fragments per group
+360 inodes per group
+
+Checking for bad blocks (read-only test): done
+Writing inode tables: done
+Writing superblocks and filesystem accounting information: done
+$
+ + The -c option is more convenient than a separate use of + badblocks, but badblocks is necessary for checking + after the filesystem has been created.

The process to prepare filesystems on hard disks or + partitions is the same as for floppies, except that the formatting + isn't needed.

Mounting and unmounting

Before one can use a filesystem, it has to be mounted. + The operating system then does various bookkeeping things to + make sure that everything works. Since all files in UNIX are + in a single directory tree, the mount operation will make it + look like the contents of the new filesystem are the contents of + an existing subdirectory in some already mounted filesystem.

For example, Figure 4-3 shows three + separate filesystems, each with their own root directory. + When the last two filesystems are mounted below /home + and /usr, respectively, on the first filesystem, we + can get a single directory tree, as in + Figure 4-4.

Figure 4-3. Three separate filesystems.

Figure 4-4. /home and /usr have been mounted.

The mounts could be done as in the following example: + +

$ mount /dev/hda2 /home
+$ mount /dev/hda3 /usr
+$
+ + The mount command takes two arguments. + The first one is the device file corresponding to the disk + or partition containing the filesystem. The second one is + the directory below which it will be mounted. After these + commands the contents of the two filesystems look just + like the contents of the /home and + /usr directories, respectively. One would + then say that ``/dev/hda2 is + mounted on /home'', and + similarly for /usr. To look at either + filesystem, one would look at the contents of the directory + on which it has been mounted, just as if it were any other + directory. Note the difference between the device file, + /dev/hda2, and the mounted-on directory, + /home. The device file gives access to the + raw contents of the disk, the mounted-on directory gives access + to the files on the disk. The mounted-on directory is called + the mount point.

Linux supports many filesystem types. mount tries to + guess the type of the filesystem. You can also use the + -t fstype option to specify the type directly; + this is sometimes necessary, since the heuristics mount + uses do not always work. For example, to mount an MS-DOS + floppy, you could use the following command: + +

$ mount -t msdos /dev/fd0 /floppy
+$
+

The mounted-on directory need not be empty, although it + must exist. Any files in it, however, will be inaccessible by + name while the filesystem is mounted. (Any files that have + already been opened will still be accessible. Files that + have hard links from other directories can be accessed using + those names.) There is no harm done with this, and it can even + be useful. For instance, some people like to have /tmp + and /var/tmp synonymous, and make /tmp be a symbolic + link to /var/tmp. When the system is booted, before + the /var filesystem is mounted, a /var/tmp directory + residing on the root filesystem is used instead. When /var + is mounted, it will make the /var/tmp directory on the root + filesystem inaccessible. If /var/tmp didn't exist on the + root filesystem, it would be impossible to use temporary files + before mounting /var.

If you don't intend to write anything to the filesystem, use + the -r switch for mount to do a readonly + mount. This will make the kernel stop any attempts at + writing to the filesystem, and will also stop the kernel from + updating file access times in the inodes. Read-only mounts + are necessary for unwritable media, e.g., CD-ROM's.

The alert reader has already noticed a slight + logistical problem. How is the first filesystem (called the root + filesystem, because it contains the root directory) mounted, + since it obviously can't be mounted on another filesystem? + Well, the answer is that it is done by magic. + + [1] + + The root filesystem is magically mounted at boot time, + and one can rely on it to always be mounted. If the + root filesystem can't be mounted, the system does not boot. + The name of the filesystem that is magically mounted as root + is either compiled into the kernel, or set using LILO or + rdev.

The root filesystem is usually first mounted readonly. + The startup scripts will then run fsck + to verify its validity, and if there are no problems, they + will re-mount it so that writes will + also be allowed. fsck must not be run on a + mounted filesystem, since any changes to the filesystem while + fsck is running will + cause trouble. Since the root filesystem is mounted readonly + while it is being checked, fsck can fix any + problems without worry, since the remount operation will flush + any metadata that the filesystem keeps in memory.

On many systems there are other filesystems that should + also be mounted automatically at boot time. These are specified + in the /etc/fstab file; see the fstab man + page for details on the format. The details of exactly when the + extra filesystems are mounted depend on many factors, and can be + configured by each administrator if need be; see + Chapter 6.

When a filesystem no longer needs to be mounted, it can be + unmounted with umount. + + [2] + + umount takes one argument: + either the device file or the mount point. + For example, to unmount the directories of + the previous example, one could use the commands + +

$ umount /dev/hda2
+$ umount /usr
+$
+

See the man page for further instructions on how to + use the command. It is imperative that you always unmount a + mounted floppy. Don't just pop the floppy out of + the drive! Because of disk caching, the data is + not necessarily written to the floppy until you unmount it, + so removing the floppy from the drive too early might cause the + contents to become garbled. If you only read from the floppy, + this is not very likely, but if you write, even accidentally, + the result may be catastrophic.

Mounting and unmounting requires super user privileges, i.e., + only root can do it. The reason for this is that if any + user can mount a floppy on any directory, then it is rather easy + to create a floppy with, say, a Trojan horse disguised as + /bin/sh, or any other often used program. However, it is + often necessary to allow users to use floppies, and there are + several ways to do this: + +

  • Give the users the root password. This is + obviously bad security, but is the easiest solution. It works + well if there is no need for security anyway, which is the case + on many non-networked, personal systems.

  • Use a program such as sudo to allow users to + use mount. This is still bad security, but doesn't + directly give super user privileges to + everyone. + [3] +

  • Make the users use mtools, a package for manipulating + MS-DOS filesystems, without mounting them. This works + well if MS-DOS floppies are all that is needed, + but is rather awkward otherwise. +

  • List the floppy devices and their allowable mount points + together with the suitable options in /etc/fstab. + +

+ + The last alternative can be implemented by adding a line like + the following to the \fn{/etc/fstab} file: + +
/dev/fd0            /floppy      msdos   user,noauto      0     0
+ + The columns are: device file to mount, directory to mount + on, filesystem type, options, backup frequency (used by + dump), and fsck pass number + (to specify the order in which filesystems should be checked + upon boot; 0 means no check).

The noauto option stops this mount to be done + automatically when the system is started (i.e., it stops + mount -a from mounting it). The user option + allows any user to mount the filesystem, and, because of security + reasons, disallows execution of programs (normal or setuid) + and interpretation of device files from the mounted filesystem. + After this, any user can mount a floppy with an msdos + filesystem with the following command: + +

$ mount /floppy
+$
+ + The floppy can (and needs to, of course) be unmounted with + the corresponding \cmd{umount} command.

If you want to provide access to several types of floppies, + you need to give several mount points. The settings can be + different for each mount point. For example, to give access + to both MS-DOS and ext2 floppies, you could have the following + to lines in /etc/fstab: + +

/dev/fd0    /dosfloppy    msdos   user,noauto  0  0
+/dev/fd0    /ext2floppy   ext2    user,noauto  0  0
+ + For MS-DOS filesystems (not just floppies), you probably want + to restrict access to it by using the uid, + gid, and umask filesystem + options, described in detail on the mount + manual page. If you aren't careful, mounting an MS-DOS filesystem + gives everyone at least read access to the files in it, which + is not a good idea.

Checking filesystem integrity with fsck

Filesystems are complex creatures, and as such, they + tend to be somewhat error-prone. A filesystem's correctness and + validity can be checked using the fsck command. + It can be instructed to repair any minor problems it finds, and to + alert the user if there any unrepairable problems. Fortunately, + the code to implement filesystems is debugged quite effectively, + so there are seldom any problems at all, and they are usually + caused by power failures, failing hardware, or operator errors; + for example, by not shutting down the system properly.

Most systems are setup to run fsck + automatically at boot time, so that any errors are detected + (and hopefully corrected) before the system is used. Use of + a corrupted filesystem tends to make things worse: if the + data structures are messed up, using the filesystem will + probably mess them up even more, resulting in more data loss. + However, fsck can take a while to run on big + filesystems, and since errors almost never occur if the system + has been shut down properly, a couple of tricks are used to + avoid doing the checks in such cases. The first is that if + the file /etc/fastboot exists, no checks + are made. The second is that the ext2 filesystem has a special + marker in its superblock that tells whether the filesystem + was unmounted properly after the previous mount. This allows + e2fsck (the version of fsck + for the ext2 filesystem) to avoid checking the filesystem if + the flag indicates that the unmount was done (the assumption + being that a proper unmount indicates no problems). Whether the + /etc/fastboot trick works on your system + depends on your startup scripts, but the ext2 trick works + every time you use e2fsck. It has to be + explicitly bypassed with an option to e2fsck + to be avoided. (See the e2fsck man page for + details on how.)

The automatic checking only works for the + filesystems that are mounted automatically at boot time. + Use fsck manually to check other filesystems, + e.g., floppies.

If fsck finds unrepairable problems, + you need either in-depth knowlege of how filesystems work in + general, and the type of the corrupt filesystem in particular, + or good backups. The latter is easy (although sometimes tedious) + to arrange, the former can sometimes be arranged via a friend, + the Linux newsgroups and mailing lists, or some other source of + support, if you don't have the know-how yourself. I'd like to + tell you more about it, but my lack of education and experience + in this regard hinders me. The debugfs + program by Theodore T'so should be useful.

fsck must only be run on unmounted + filesystems, never on mounted filesystems (with the exception of + the read-only root during startup). This is because it accesses + the raw disk, and can therefore modify the filesystem without the + operating system realizing it. There will + be trouble, if the operating system is confused.

Checking for disk errors with badblocks

It can be a good idea to periodically check for bad blocks. + This is done with the badblocks command. It outputs + a list of the numbers of all bad blocks it can find. This list + can be fed to fsck to be recorded + in the filesystem data structures so that the operating system + won't try to use the bad blocks for storing data. + The following example will show how this could be done. + +

$ badblocks /dev/fd0H1440 1440 > bad-blocks
+$ fsck -t ext2 -l bad-blocks /dev/fd0H1440
+Parallelizing fsck version 0.5a (5-Apr-94)
+e2fsck 0.5a, 5-Apr-94 for EXT2 FS 0.5, 94/03/10
+Pass 1: Checking inodes, blocks, and sizes
+Pass 2: Checking directory structure
+Pass 3: Checking directory connectivity
+Pass 4: Check reference counts.
+Pass 5: Checking group summary information.
+
+/dev/fd0H1440: ***** FILE SYSTEM WAS MODIFIED *****
+/dev/fd0H1440: 11/360 files, 63/1440 blocks
+$
+ + If badblocks reports a block that was already used, + e2fsck will try to move the block to another + place. If the block was really bad, not just marginal, the + contents of the file may be corrupted.

Fighting fragmentation

When a file is written to disk, it can't always be written + in consecutive blocks. A file that is not stored in + consecutive blocks is fragmented. It takes longer + to read a fragmented file, since the disk's read-write head + will have to move more. It is desireable to avoid fragmentation, + although it is less of a problem in a system with a good buffer + cache with read-ahead.

The ext2 filesystem attempts to keep fragmentation at a + minimum, by keeping all blocks in a file close together, even if + they can't be stored in consecutive sectors. Ext2 effectively + always allocates the free block that is nearest to other blocks + in a file. For ext2, it is therefore seldom necessary to worry + about fragmentation. There is a program for defragmenting an + ext2 filesystem, see XXX (ext2-defrag) in the bibliography.

There are many MS-DOS defragmentation programs that + move blocks around in the filesystem to remove fragmentation. + For other filesystems, defragmentation must be done by backing + up the filesystem, re-creating it, and restoring the files + from backups. Backing up a filesystem before defragmening is + a good idea for all filesystems, since many things can go wrong + during the defragmentation.

Other tools for all filesystems

Some other tools are also useful for managing filesystems. + df shows the free disk space on one or more + filesystems; du shows how much disk space a + directory and all its files contain. These can be used to hunt + down disk space wasters.

sync forces all unwritten blocks + in the buffer cache (see the section called The buffer cache in Chapter 5) to + be written to disk. It is seldom necessary to do this by + hand; the daemon process update does + this automatically. It can be useful in catastrophies, + for example if update or its helper + process bdflush dies, or if you must + turn off power now and can't wait for + update to run.

Other tools for the ext2 filesystem

In addition to the filesystem creator (mke2fs) and + checker (e2fsck) accessible directly or via the + filesystem type independent front ends, the ext2 + filesystem has some additional tools that can be useful.

tune2fs adjusts filesystem parameters. Some of the + more interesting parameters are: + +

  • A maximal mount count. e2fsck enforces a check when + filesystem has been mounted too many times, even if + the clean flag is set. For a system that is used for + developing or testing the system, it might be a good + idea to reduce this limit. +

  • A maximal time between checks. e2fsck can also enforce + a maximal time between two checks, even if the clean + flag is set, and the filesystem hasn't been mounted very + often. This can be disabled, however. +

  • Number of blocks reserved for root. Ext2 + reserves some blocks for root so that if the + filesystem fills up, it is still possible to do system + administration without having to delete anything. The + reserved amount is by default 5 percent, which on most disks + isn't enough to be wasteful. However, for floppies there + is no point in reserving any blocks. +

+ + See the tune2fs manual page for more + information.

dumpe2fs shows information about an ext2 filesystem, mostly + from the superblock. Figure 4-5 shows + a sample output. Some of the information in the output is + technical and requires understanding of how the filesystem + works (see appendix XXX ext2fspaper), but much of + it is readily understandable even for layadmins.

Figure 4-5. Sample output from dumpe2fs

dumpe2fs 0.5b, 11-Mar-95 for EXT2 FS 0.5a, 94/10/23
+Filesystem magic number:  0xEF53
+Filesystem state:         clean
+Errors behavior:          Continue
+Inode count:              360
+Block count:              1440
+Reserved block count:     72
+Free blocks:              1133
+Free inodes:              326
+First block:              1
+Block size:               1024
+Fragment size:            1024
+Blocks per group:         8192
+Fragments per group:      8192
+Inodes per group:         360
+Last mount time:          Tue Aug  8 01:52:52 1995
+Last write time:          Tue Aug  8 01:53:28 1995
+Mount count:              3
+Maximum mount count:      20
+Last checked:             Tue Aug  8 01:06:31 1995
+Check interval:           0
+Reserved blocks uid:      0 (user root)
+Reserved blocks gid:      0 (group root)
+
+Group 0:
+  Block bitmap at 3, Inode bitmap at 4, Inode table at 5
+  1133 free blocks, 326 free inodes, 2 directories
+  Free blocks: 307-1439
+  Free inodes: 35-360

debugfs is a filesystem debugger. + It allows direct access to the filesystem data structures + stored on disk and can thus be used to repair a disk that is so + broken that fsck can't fix it automatically. + It has also been known to be used to recover deleted files. + However, debugfs very much requires that + you understand what you're doing; a failure to understand can + destroy all your data.

dump and restore can be used to back up an + ext2 filesystem. They are ext2 specific versions of the + traditional UNIX backup tools. See Chapter 10 + for more information on backups.

Notes

[1]

For more + information, see the kernel source or the Kernel Hackers' + Guide.

[2]

It should of course be + unmount, but the n mysteriously disappeared in + the 70's, and hasn't been seen since. Please return it to Bell + Labs, NJ, if you find it.

[3]

It requires several seconds of hard + thinking on the users' behalf.

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Disks without filesystems

Not all disks or partitions are used as filesystems. + A swap partition, for example, will not have a filesystem on it. + Many floppies are used in a tape-drive emulating fashion, so that + a tar or other file is written directly on + the raw disk, without a filesystem. Linux boot floppies don't + contain a filesystem, only the raw kernel.

Avoiding a filesystem has the advantage of making more of + the disk usable, since a filesystem always has some bookkeeping + overhead. It also makes the disks more easily compatible + with other systems: for example, the tar + file format is the same on all systems, while filesystems are + different on most systems. You will quickly get used to disks + without filesystems if you need them. Bootable Linux floppies + also do not necessarily have a filesystem, although that is + also possible.

One reason to use raw disks is to make image copies of them. + For instance, if the disk contains a partially damaged filesystem, + it is a good idea to make an exact copy of it before trying to + fix it, since then you can start again if your fixing breaks things + even more. One way to do this is to use dd: + +

$ dd if=/dev/fd0H1440 of=floppy-image
+2880+0 records in
+2880+0 records out
+$ dd if=floppy-image of=/dev/fd0H1440
+2880+0 records in
+2880+0 records out
+$
+ + The first dd makes an exact image of the + floppy to the file floppy-image, the second + one writes the image to the floppy. (The user has presumably + switched the floppy before the second command. Otherwise the + command pair is of doubtful usefulness.)

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Allocating disk space

Partitioning schemes

It is not easy to partition a disk in the best possible way. + Worse, there is no universally correct way to do it; there are + too many factors involved.

The traditional way is to have a (relatively) small + root filesystem, which contains /bin, + /etc, /dev, + /lib, /tmp, and other + stuff that is needed to get the system up and running. This way, + the root filesystem (in its own partition or on its own disk) + is all that is needed to bring up the system. The reasoning is + that if the root filesystem is small and is not heavily used, + it is less likely to become corrupt when the system crashes, and + you will therefore find it easier to fix any problems caused by + the crash. Then you create separate partitions or use separate + disks for the directory tree below /usr, the + users' home directories (often under /home), + and the swap space. Separating the home directories (with the + users' files) in their own partition makes backups easier, since + it is usually not necessary to backup programs (which reside + below /usr). In a networked environment it + is also possible to share /usr among several + machines (e.g., by using NFS), thereby reducing the total disk + space required by several tens or hundreds of megabytes times + the number of machines.

The problem with having many partitions is that it splits + the total amount of free disk space into many small pieces. + Nowadays, when disks and (hopefully) operating systems are + more reliable, many people prefer to have just one partition + that holds all their files. On the other hand, it can be less + painful to back up (and restore) a small partition.

For a small hard disk (assuming you don't do kernel + development), the best way to go is probably to have just one + partition. For large hard disks, it is probably + better to have a few large partitions, just in case + something does go wrong. (Note that `small' and `large' are + used in a relative sense here; your needs for disk space + decide what the threshold is.)

If you have several disks, you might wish to have the + root filesystem (including /usr) on one, + and the users' home directories on another.

It is a good idea to be prepared to experiment a bit + with different partitioning schemes (over time, not just + while first installing the system). This is a bit of work, + since it essentially requires you to install the system from + scratch several times, but it is the only way to be sure you do + it right.

Space requirements

The Linux distribution you install will give some indication + of how much disk space you need for various configurations. + Programs installed separately may also do the same. This will + help you plan your disk space usage, but you should prepare + for the future and reserve some extra space for things you will + notice later that you need.

The amount you need for user files depends on what your + users wish to do. Most people seem to need as much space for + their files as possible, but the amount they will live happily + with varies a lot. Some people do only light text processing + and will survive nicely with a few megabytes, others do heavy + image processing and will need gigabytes.

By the way, when comparing file sizes given in + kilobytes or megabytes and disk space given in megabytes, it + can be important to know that the two units can be different. + Some disk manufacturers like to pretend that a kilobyte is 1000 + bytes and a megabyte is 1000 kilobytes, while all the rest of + the computing world uses 1024 for both factors. Therefore, + my 345 MB hard disk was really a 330 MB hard disk. + + [1] +

Swap space allocation is discussed in the section called Allocating swap space in Chapter 5.

Examples of hard disk allocation

I used to have a 109 MB hard disk. Now I am using a 330 MB + hard disk. I'll explain how and why I partitioned these + disks.

The 109 MB disk I partitioned in a lot of ways, when my + needs and the operating systems I used changed; I'll explain + two typical scenarios. First, I used to run MS-DOS together + with Linux. For that, I needed about 20 MB of hard disk, or + just enough to have MS-DOS, a C compiler, an editor, a few other + utilities, the program I was working on, and enough free disk + space to not feel claustrophobic. For Linux, I had a 10 MB swap + partition, and the rest, or 79 MB, was a single partition with all + the files I had under Linux. I experimented with having separate + root, /usr, and /home + partitions, but there was never enough free disk space in one + piece to do much interesting.

When I didn't need MS-DOS anymore, I repartitioned the + disk so that I had a 12 MB swap partition, and again had the + rest as a single filesystem.

The 330 MB disk is partitioned into several partitions, like + this: + +

5 MBroot filesystem
10 MBswap partition
180 MB\fn{/usr} filesystem
120 MB\fn{/home} filesystem
15 MBscratch partition

+ + The scratch partition is for playing around with things that + require their own partition, e.g., trying different Linux + distributions, or comparing speeds of filesystems. When not + needed for anything else, it is used as swap space (I like to + have a lot of open windows).

Adding more disk space for Linux

Adding more disk space for Linux is easy, at least after the + hardware has been properly installed (the hardware installation + is outside the scope of this book). You format it if necessary, + then create the partitions and filesystem as described above, + and add the proper lines to /etc/fstab + so that it is mounted automatically.

Tips for saving disk space

The best tip for saving disk space is to avoid installing + unnecessary programs. Most Linux distributions have an + option to install only part of the packages they contain, + and by analyzing your needs you might notice that you don't + need most of them. This will help save a lot of disk space, + since many programs are quite large. Even if you do need a + particular package or program, you might not need all of it. + For example, some on-line documentation might be unnecessary, + as might some of the Elisp files for GNU Emacs, some of the + fonts for X11, or some of the libraries for programming.

If you cannot uninstall packages, you might look into + compression. Compression programs such as gzip + or zip will compress (and uncompress) + individual files or groups of files. The gzexe + system will compress and uncompress programs invisibly to the + user (unused programs are compressed, then uncompressed as they + are used). The experimental DouBle system will compress all + files in a filesystem, invisibly to the programs that use them. + (If you are familiar with products such as Stacker for MS-DOS, + the principle is the same.)

Notes

[1]

Sic transit discus mundi.

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Creating a swap space

A swap file is an ordinary file; it is in no way special + to the kernel. The only thing that matters to the kernel is + that it has no holes, and that it is prepared for use with + mkswap. It must reside on a local disk, + however; it can't reside in a filesystem that has been mounted + over NFS due to implementation reasons.

The bit about holes is important. The swap file reserves + the disk space so that the kernel can quickly swap out a page + without having to go through all the things that are necessary + when allocating a disk sector to a file. The kernel merely + uses any sectors that have already been allocated to the file. + Because a hole in a file means that there are no disk sectors + allocated (for that place in the file), it is not good for the + kernel to try to use them.

One good way to create the swap file without holes is through + the following command: + +

$ dd if=/dev/zero of=/extra-swap bs=1024 count=1024
+1024+0 records in
+1024+0 records out
+$
+ + where /extra-swap is the name of the swap + file and the size of is given after the count=. + It is best for the size to be a multiple of 4, because the + kernel writes out memory pages, which + are 4 kilobytes in size. If the size is not a multiple of 4, + the last couple of kilobytes may be unused.

A swap partition is also not special in any way. You create + it just like any other partition; the only difference is that + it is used as a raw partition, that is, it will not contain any + filesystem at all. It is a good idea to mark swap partitions + as type 82 (Linux swap); this will the make partition listings + clearer, even though it is not strictly necessary to the + kernel.

After you have created a swap file or a swap partition, you + need to write a signature to its beginning; this contains some + administrative information and is used by the kernel. The + command to do this is \cmd{mkswap}, used like this: + +

$ mkswap /extra-swap 1024
+Setting up swapspace, size = 1044480 bytes
+$
+ + Note that the swap space is still not in use yet: it exists, + but the kernel does not use it to provide virtual memory.

You should be very careful when using + mkswap, since it does not check that the + file or partition isn't used for anything else. You + can easily overwrite important files and partitions with + mkswap! Fortunately, you should + only need to use mkswap when you install + your system.

The Linux memory manager limits the size of each swap space to + about 127 MB (for various technical reasons, the actual limit + is (4096-10) * 8 * 4096 = 133890048$ bytes, or + 127.6875 megabytes). You can, however, use up to + 16 swap spaces simultaneously, for a total of almost + 2 GB. + + [1] + +

Notes

[1]

A gigabyte here, a gigabyte there, pretty + soon we start talking about real memory.

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Using a swap space

An initialized swap space is taken into use with + swapon. This command tells the kernel that + the swap space can be used. The path to the swap space is given + as the argument, so to start swapping on a temporary swap file + one might use the following command. + +

$ swapon /extra-swap
+$
+ + Swap spaces can be used automatically by listing them in + the /etc/fstab file. + +
/dev/hda8        none        swap        sw     0     0
+/swapfile        none        swap        sw     0     0
+ + The startup scripts will run the command swapon + -a, which will start swapping on all the swap + spaces listed in /etc/fstab. Therefore, + the swapon command is usually used only when + extra swap is needed.

You can monitor the use of swap spaces with + free. It will tell the total amount of swap + space used. + +

$ free
+             total       used       free     shared    buffers
+Mem:         15152      14896        256      12404       2528
+-/+ buffers:            12368       2784
+Swap:        32452       6684      25768
+$
+ + The first line of output (Mem:) shows the + physical memory. The total column does not show the physical + memory used by the kernel, which is usually about a megabyte. + The used column shows the amount of memory used (the second + line does not count buffers). The free column shows completely + unused memory. The shared column shows the amount of memory + shared by several processes; the more, the merrier. The buffers + column shows the current size of the disk buffer cache.

That last line (Swap:) shows similar + information for the swap spaces. If this line is all zeroes, + your swap space is not activated.

The same information is available via + top, or using the proc filesystem in file + /proc/meminfo. It is currently difficult + to get information on the use of a specific swap space.

A swap space can be removed from use with + swapoff. It is usually not necessary to do it, + except for temporary swap spaces. Any pages in use in the swap + space are swapped in first; if there is not sufficient physical + memory to hold them, they will then be swapped out (to some other + swap space). If there is not enough virtual memory to hold all + of the pages Linux will start to thrash; after a long while it + should recover, but meanwhile the system is unusable. You should + check (e.g., with free) that there is enough + free memory before removing a swap space from use.

All the swap spaces that are used automatically + with swapon -a can be removed from use + with swapoff -a; it looks at the file + /etc/fstab to find what to remove. + Any manually used swap spaces will remain in use.

Sometimes a lot of swap space can be in use even though + there is a lot of free physical memory. This can happen for + instance if at one point there is need to swap, but later a big + process that occupied much of the physical memory terminates + and frees the memory. The swapped-out data is not automatically + swapped in until it is needed, so the physical memory may remain + free for a long time. There is no need to worry about this, + but it can be comforting to know what is happening.

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Sharing swap spaces with other operating systems

Virtual memory is built into many operating systems. + Since they each need it only when they are running, i.e., never at + the same time, the swap spaces of all but the currently running + one are being wasted. It would be more efficient for them to + share a single swap space. This is possible, but can require a + bit of hacking. The Tips-HOWTO contains some advice on how to + implement this.

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Allocating swap space

Some people will tell you that you should allocate twice as much + swap space as you have physical memory, but this is a bogus rule. + Here's how to do it properly: + +

  • Estimate your total memory needs. This is the largest + amount of memory you'll probably need at a time, that is the + sum of the memory requirements of all the programs you want to + run at the same time. This can be done by running at the same + time all the programs you are likely to ever be running at the + same time.

    For instance, if you want to run X, you should allocate + about 8 MB for it, gcc wants several megabytes (some + files need an unusually large amount, up to tens of + megabytes, but usually about four should do), and so on. + The kernel will use about a megabyte by itself, and the + usual shells and other small utilities perhaps a few + hundred kilobytes (say a megabyte together). There is + no need to try to be exact, rough estimates are fine, + but you might want to be on the pessimistic side.

    Remember that if there are going to be several people + using the system at the same time, they are all going + to consume memory. However, if two people run the same + program at the same time, the total memory consumption + is usually not double, since code pages and shared + libraries exist only once.

    The free and ps + commands are useful for estimating the memory needs. + +

  • Add some security to the estimate in step 1. This is because + estimates of program sizes will probably be wrong, because + you'll probably forget some programs you want to run, and to + make certain that you have some extra space just in case. A + couple of megabytes should be fine. (It is better to allocate + too much than too little swap space, but there's no need to + over-do it and allocate the whole disk, since unused swap space + is wasted space; see later about adding more swap.) Also, + since it is nicer to deal with even numbers, you can round the + value up to the next full megabyte.

  • Based on the computations above, you know how much memory + you'll be needing in total. So, in order to allocate swap + space, you just need to subtract the size of your physical + memory from the total memory needed, and you know how much + swap space you need. (On some versions of UNIX, you need to + allocate space for an image of the physical memory as well, so + the amount computed in step 2 is what you need and you shouldn't + do the subtraction.)

  • If your calculated swap space is very much larger than your + physical memory (more than a couple times larger), you should + probably invest in more physical memory, otherwise performance + will be too low.

+ +

It's a good idea to have at least some swap space, even if + your calculations indicate that you need none. Linux uses + swap space somewhat aggressively, so that as much physical + memory as possible can be kept free. Linux will swap out + memory pages that have not been used, even if the memory + is not yet needed for anything. This avoids waiting for + swapping when it is needed: the swapping can be done + earlier, when the disk is otherwise idle.

Swap space can be divided among several disks. This + can sometimes improve performance, depending on the + relative speeds of the disks and the access patterns + of the disks. You might want to experiment with a few + schemes, but be aware that doing the experiments + properly is quite difficult. You should not believe + claims that any one scheme is superior to any other, + since it won't always be true. +

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The buffer cache

Reading from a disk + + [1] + + is very slow compared to accessing (real) memory. In addition, + it is common to read the same part of a disk several times + during relatively short periods of time. For example, one + might first read an e-mail message, then read the letter into + an editor when replying to it, then make the mail program read + it again when copying it to a folder. Or, consider how often + the command ls might be run on a system with + many users. By reading the information from disk only once + and then keeping it in memory until no longer needed, one can + speed up all but the first read. This is called disk + buffering, and the memory used for the purpose is + called the buffer cache.

Since memory is, unfortunately, a finite, nay, scarce + resource, the buffer cache usually cannot be big enough (it + can't hold all the data one ever wants to use). When the cache + fills up, the data that has been unused for the longest time + is discarded and the memory thus freed is used for the new + data.

Disk buffering works for writes as well. On the one hand, + data that is written is often soon read again (e.g., a source + code file is saved to a file, then read by the compiler), + so putting data that is written in the cache is a good idea. + On the other hand, by only putting the data into the cache, not + writing it to disk at once, the program that writes runs quicker. + The writes can then be done in the background, without slowing + down the other programs.

Most operating systems have buffer caches (although + they might be called something else), but not all of + them work according to the above principles. Some are + write-through: the data is written to disk + at once (it is kept in the cache as well, of course). The cache + is called write-back if the writes are done + at a later time. Write-back is more efficient than write-through, + but also a bit more prone to errors: if the machine crashes, + or the power is cut at a bad moment, or the floppy is removed + from the disk drive before the data in the cache waiting to be + written gets written, the changes in the cache are usually lost. + This might even mean that the filesystem (if there is one) is + not in full working order, perhaps because the unwritten data + held important changes to the bookkeeping information.

Because of this, you should never turn off the + power without using a proper shutdown procedure (see Chapter 6), or remove a floppy from the + disk drive until it has been unmounted (if it was mounted) + or after whatever program is using it has signaled that it + is finished and the floppy drive light doesn't shine anymore. + The sync command flushes + the buffer, i.e., forces all unwritten data to be written to disk, + and can be used when one wants to be sure that everything is + safely written. In traditional UNIX systems, there is a program + called update running in the background + which does a sync every 30 seconds, so + it is usually not necessary to use sync. + Linux has an additional daemon, bdflush, + which does a more imperfect sync more frequently to avoid the + sudden freeze due to heavy disk I/O that sync + sometimes causes.

Under Linux, bdflush is started by + update. There is usually no reason to worry + about it, but if bdflush happens to die for + some reason, the kernel will warn about this, and you should + start it by hand (/sbin/update).

The cache does not actually buffer files, but blocks, which + are the smallest units of disk I/O (under Linux, they are usually + 1 kB). This way, also directories, super blocks, other filesystem + bookkeeping data, and non-filesystem disks are cached.

The effectiveness of a cache is primarily decided by its + size. A small cache is next to useless: it will hold so little + data that all cached data is flushed from the cache before it + is reused. The critical size depends on how much data is read + and written, and how often the same data is accessed. The only + way to know is to experiment.

If the cache is of a fixed size, it is not very good to have + it too big, either, because that might make the free memory too + small and cause swapping (which is also slow). To make the most + efficient use of real memory, Linux automatically uses all free + RAM for buffer cache, but also automatically makes the cache + smaller when programs need more memory.

Under Linux, you do not need to do anything to make use + of the cache, it happens completely automatically. Except for + following the proper procedures for shutdown and removing + floppies, you do not need to worry about it.

Notes

[1]

Except a RAM disk, for obvious + reasons.

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Allocating swap spaceUpBoots And Shutdowns
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The boot process in closer look

You can boot Linux either from a floppy or from the hard + disk. The installation section in the Installation and + Getting Started guide (XXX citation) + tells you how to install Linux so you can boot it the way + you want to.

When a PC is booted, the BIOS will do various tests to + check that everything looks all right, + + [1] + + and will then start the actual booting. It will choose a disk + drive (typically the first floppy drive, if there is a floppy + inserted, otherwise the first hard disk, if one is installed + in the computer; the order might be configurable, however) + and will then read its very first sector. This is called the + boot sector; for a hard disk, it is also + called the master boot record, since a + hard disk can contain several partitions, each with their own + boot sectors.

The boot sector contains a small program (small enough to + fit into one sector) whose responsibility is to read the actual + operating system from the disk and start it. When booting Linux + from a floppy disk, the boot sector contains code that just reads + the first few hundred blocks (depending on the actual kernel + size, of course) to a predetermined place in memory. On a Linux + boot floppy, there is no filesystem, the kernel is just stored + in consecutive sectors, since this simplifies the boot process. + It is possible, however, to boot from a floppy with a filesystem, + by using LILO, the LInux LOader.

When booting from the hard disk, the code in the master + boot record will examine the partition table (also in the master + boot record), identify the active partition (the partition that is + marked to be bootable), read the boot sector from that partition, + and then start the code in that boot sector. The code in the + partition's boot sector does what a floppy disk's boot sector + does: it will read in the kernel from the partition and start it. + The details vary, however, since it is generally not useful to + have a separate partition for just the kernel image, so the + code in the partition's boot sector can't just read the disk + in sequential order, it has to find the sectors wherever the + filesystem has put them. There are several ways around this + problem, but the most common way is to use LILO. (The details + about how to do this are irrelevant for this discussion, however; + see the LILO documentation for more information; it is most + thorough.)

When booting with LILO, it will normally go right ahead + and read in and boot the default kernel. It is also possible + to configure LILO to be able to boot one of several kernels, + or even other operating systems than Linux, and it is possible + for the user to choose which kernel or operating system is to + be booted at boot time. LILO can be configured so that if one + holds down the alt, shift, or + ctrl key at boot time (when LILO is loaded), + LILO will ask what is to be booted and not boot the default + right away. Alternatively, LILO can be configured so that it + will always ask, with an optional timeout that will cause the + default kernel to be booted.

With LILO, it is also possible to give a kernel + command line argument, after the name of the kernel + or operating system.

Booting from floppy and from hard disk have both their + advantages, but generally booting from the hard disk is nicer, + since it avoids the hassle of playing around with floppies. + It is also faster. However, it can be more troublesome to install + the system to boot from the hard disk, so many people will first + boot from floppy, then, when the system is otherwise installed + and working well, will install LILO and start booting from the + hard disk.

After the Linux kernel has been read into the memory, by + whatever means, and is started for real, roughly the following + things happen: + +

  • The Linux kernel is installed compressed, so it will first + uncompress itself. The beginning of the kernel image + contains a small program that does this. +

  • If you have a super-VGA card that Linux + recognizes and that has some special text modes (such as 100 + columns by 40 rows), Linux asks you which mode + you want to use. During the kernel compilation, it is + possible to preset a video mode, so that this is never asked. + This can also be done with LILO or rdev. +

  • After this, the kernel checks what other hardware there is + (hard disks, floppies, network adapters, etc), and configures + some of its device drivers appropriately; while it does this, + it outputs messages about its findings. For example, when I + boot, I it looks like this: + +

    LILO boot:
+Loading linux.
+Console: colour EGA+ 80x25, 8 virtual consoles
+Serial driver version 3.94 with no serial options enabled
+tty00 at 0x03f8 (irq = 4) is a 16450
+tty01 at 0x02f8 (irq = 3) is a 16450
+lp_init: lp1 exists (0), using polling driver
+Memory: 7332k/8192k available (300k kernel code, 384k reserved, 176k data)
+Floppy drive(s): fd0 is 1.44M, fd1 is 1.2M
+Loopback device init
+Warning WD8013 board not found at i/o = 280.
+Math coprocessor using irq13 error reporting.
+Partition check:
+  hda: hda1 hda2 hda3
+VFS: Mounted root (ext filesystem).
+Linux version 0.99.pl9-1 (root@haven) 05/01/93 14:12:20
    + + The exact texts are different on different systems, depending + on the hardware, the version of Linux being used, and how + it has been configured. +

  • Then the kernel will try to mount the root + filesystem. The place is configurable at compilation time, or + any time with rdev or LILO. The filesystem + type is detected automatically. If the mounting of the root + filesystem fails, for example because you didn't remember to + include the corresponding filesystem driver in the kernel, the + kernel panics and halts the system (there isn't much it can do, + anyway).

    The root filesystem is usually mounted read-only (this can + be set in the same way as the place). This makes it possible + to check the filesystem while it is mounted; it is not a good + idea to check a filesystem that is mounted read-write. +

  • After this, the kernel starts + the program init (located in + /sbin/init) in the background (this will + always become process number 1). init does + various startup chores. The exact things it does depends on how + it is configured; see Chapter 7 for more information + (not yet written). It will at least start some essential + background daemons.

  • init then switches to + multi-user mode, and starts a getty for virtual + consoles and serial lines. getty is the + program which lets people log in via virtual consoles and serial + terminals. init may also start some other + programs, depending on how it is configured.

  • After this, the boot is complete, and the system + is up and running normally.

+

Notes

[1]

This is called + the power on self test, or + POST for short.

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Boots And ShutdownsUpMore about shutdowns
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More about shutdowns

It is important to follow the correct procedures when you shut + down a Linux system. If you fail do so, your filesystems probably + will become trashed and the files probably will become scrambled. + This is because Linux has a disk cache that won't write things + to disk at once, but only at intervals. This greatly improves + performance but also means that if you just turn off the power + at a whim the cache may hold a lot of data and that what is on + the disk may not be a fully working filesystem (because only + some things have been written to the disk).

Another reason against just flipping the power switch is that + in a multi-tasking system there can be lots of things going on + in the background, and shutting the power can be quite + disastrous. By using the proper shutdown sequence, you ensure + that all background processes can save their data.

The command for properly shutting down a Linux system + is shutdown. It is usually used in one of + two ways.

If you are running a system where you are the only user, + the usual way of using shutdown is to quit + all running programs, log out on all virtual consoles, log + in as root on one of them (or stay logged in as root if you + already are, but you should change to root's home directory or + the root directory, to avoid problems with unmounting), then + give the command shutdown -h now (substitute + now with a plus sign and a number in minutes + if you want a delay, though you usually don't on a single user + system).

Alternatively, if your system has many users, use the command + shutdown -h +time message, where time + is the + time in minutes until the system is halted, and message + is a short explanation of why the system is shutting down. + +

# shutdown -h +10 'We will install a new disk.  System should
+> be back on-line in three hours.'
+#
+ + This will warn everybody that the system will shut down in + ten minutes, and that they'd better get lost or lose data. + The warning is printed to every terminal on which someone is + logged in, including all xterms: + +
Broadcast message from root (ttyp0) Wed Aug  2 01:03:25 1995...
+
+We will install a new disk.  System should
+be back on-line in three hours.
+The system is going DOWN for system halt in 10 minutes !!
+ + The warning is automatically repeated a few times before the boot, + with shorter and shorter intervals as the time runs out.

When the real shutting down starts after any delays, all + filesystems (except the root one) are unmounted, user processes + (if anybody is still logged in) are killed, daemons are shut down, + all filesystem are unmounted, and generally everything settles + down. When that is done, init prints out a + message that you can power down the machine. Then, and only then, + should you move your fingers towards the power switch.

Sometimes, although rarely on any good system, it is + impossible to shut down properly. For instance, if the kernel + panics and crashes and burns and generally misbehaves, it might + be completely impossible to give any new commands, hence shutting + down properly is somewhat difficult, and just about everything + you can do is hope that nothing has been too severely damaged + and turn off the power. If the troubles are a bit less severe + (say, somebody hit your keyboard with an axe), and the kernel + and the update program still run normally, + it is probably a good idea to wait a couple of minutes to give + update a chance to flush the buffer cache, + and only cut the power after that.

Some people like to shut down using the command + sync + + [1] + + three times, waiting for the disk I/O to stop, then turn off + the power. If there are no running programs, this is about + equivalent to using shutdown. However, it + does not unmount any filesystems and this can lead to problems + with the ext2fs ``clean filesystem'' flag. The triple-sync + method is not recommended.

(In case you're wondering: the reason for three syncs is + that in the early days of UNIX, when the commands were + typed separately, that usually gave sufficient time for most + disk I/O to be finished.) +

Notes

[1]

sync flushes the + buffer cache.

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The boot process in closer lookUpRebooting
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Rebooting

Rebooting means booting the system again. This can be + accomplished by first shutting it down completely, turning + power off, and then turning it back on. A simpler way is to + ask shutdown to reboot the system, instead + of merely halting it. This is accomplished by using the + -r option to shutdown, + for example, by giving the command shutdown -r + now.

Most Linux systems run shutdown -r now + when ctrl-alt-del is pressed on the keyboard. This reboots the + system. The action on ctrl-alt-del is configurable, however, and + it might be better to allow for some delay before the reboot on + a multiuser machine. Systems that are physically accessible to + anyone might even be configured to do nothing when ctrl-alt-del + is pressed.

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More about shutdownsUpSingle user mode
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Single user mode

The shutdown command can also be used + to bring the system down to single user mode, in which no one + can log in, but root can use the console. This is useful for + system administration tasks that can't be done while the system is + running normally.

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RebootingUpEmergency boot floppies
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Emergency boot floppies

It is not always possible to boot a computer from the hard disk. + For example, if you make a mistake in configuring LILO, you might + make your system unbootable. For these situations, you need an + alternative way of booting that will always work (as long as the + hardware works). For typical PC's, this means booting from the + floppy drive.

Most Linux distributions allow one to create an + emergency boot floppy during installation. + It is a good idea to do this. However, some such boot disks + contain only the kernel, and assume you will be using the programs + on the distribution's installation disks to fix whatever problem + you have. Sometimes those programs aren't enough; for example, + you might have to restore some files from backups made with + software not on the installation disks.

Thus, it might be necessary to create a custom root floppy + as well. The Bootdisk HOWTO by Graham + Chapman (XXX citation) contains instructions for doing this. + You must, of course, remember to keep your emergency boot and + root floppies up to date.

You can't use the floppy drive you use to mount the root + floppy for anything else. This can be inconvenient if you only + have one floppy drive. However, if you have enough memory, you + can configure your boot floppy to load the root disk to a ramdisk + (the boot floppy's kernel needs to be specially configured for + this). Once the root floppy has been loaded into the ramdisk, + the floppy drive is free to mount other disks.

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Single user modeUpinit
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Configuring init to start getty: the /etc/inittab file

When it starts up, init reads the /etc/inittab + configuration file. While the system is running, it will + re-read it, if sent the HUP signal; + + [1] + + this feature makes it unnecessary to boot the system to make + changes to the init configuration take + effect.

The /etc/inittab file is + a bit complicated. We'll start with the simple case + of configuring getty lines. Lines in + /etc/inittab consist of four colon-delimited + fields: + +

id:runlevels:action:process
+ + The fields are described below. In addition, + /etc/inittab can contain empty lines, and + lines that begin with a number sign (`#'); + these are both ignored. + +
id

This identifies the line in the file. For + getty lines, it specifies the terminal + it runs on (the characters after /dev/tty + in the device file name). For other lines, + it doesn't matter (except for length restrictions), + but it should be unique. +

runlevels

The run levels the line should be considered + for. The run levels are given as single digits, + without delimiters. (Run levels are described + in the next section.) +

action

What action should be taken by the line, e.g., + respawn to run the command in the + next field again, when it exits, or once + to run it just once. +

process

The command to run. +

+ + To start a getty on the first virtual terminal + (/dev/tty1}), in all the normal multi-user + run levels (2-5), one would write the following line: + +
1:2345:respawn:/sbin/getty 9600 tty1
+ + The first field says that this is the line for /dev/tty1. + The second field says that it applies to run levels 2, 3, 4, + and 5. The third field means that the command should be run + again, after it exits (so that one can log in, log out, and + then log in again). The last field is the command that runs + getty on the first virtual terminal. + + [2] +

If you wanted to add terminals or dial-in modem lines to a + system, you'd add more lines to /etc/inittab, + one for each terminal or dial-in line. For more details, see the + manual pages init, inittab, + and getty.

If a command fails when it starts, + and init is configured to + restart it, it will use a lot of + system resources: init starts it, + it fails, init starts it, it fails, + init starts it, it fails, and so on, ad + infinitum. To prevent this, init will keep + track of how often it restarts a command, and if the frequency + grows to high, it will delay for five minutes before restarting + again.

Notes

[1]

Using the command kill -HUP + 1 as root, for example

[2]

Different versions of + getty are run differently. Consult + your manual page, and make sure it is the correct + manual page.

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initUpRun levels
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Run levels

A run level is a state of + init and the whole system that defines what + system services are operating. Run levels are identified by + numbers, see Table 7-1. There is no consensus of how to use the + user defined run levels (2 through 5). Some system administrators + use run levels to define which subsystems are working, e.g., + whether X is running, whether the network is operational, and + so on. Others have all subsystems always running or start and + stop them individually, without changing run levels, since run + levels are too coarse for controlling their systems. You need + to decide for yourself, but it might be easiest to follow the + way your Linux distribution does things.

Table 7-1. Run level numbers

0Halt the system.
1Single-user mode (for special administration).
2-5Normal operation (user defined).
6Reboot.

Run levels are configured in /etc/inittab by lines like + the following: + +

l2:2:wait:/etc/init.d/rc 2
+ + The first field is an arbitrary label, the second one means + that this applies for run level 2. The third field means + that init should run the command in the + fourth field once, when the run level is entered, and that + init should wait for it to complete. The + /etc/init.d/rc command runs whatever + commands are necessary to start and stop services to enter run + level 2.

The command in the fourth field does all the hard work of + setting up a run level. It starts services that aren't already + running, and stops services that shouldn't be running in the + new run level any more. Exactly what the command is, and how run + levels are configured, depends on the Linux distribution.

When init starts, it looks for a line + in /etc/inittab that specifies the default + run level: + +

id:2:initdefault:
+ + You can ask init to go to a non-default run + level at startup by giving the kernel a command line argument + of single or emergency. + Kernel command line arguments can be given via LILO, for example. + This allows you to choose the single user mode (run level 1).

While the system is running, the telinit + command can change the run level. When the run level is + changed, init runs the relevant command from + /etc/inittab.

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Special configuration in /etc/inittab

The /etc/inittab has some special + features that allow init to react to special + circumstances. These special features are marked by special + keywords in the third field. Some examples: + +

powerwait

Allows init to shut the system + down, when the power fails. This assumes the use of + a UPS, and software that watches the UPS and informs + init that the power is off. +

ctrlaltdel

Allows init to reboot the system, when + the user presses ctrl-alt-del on the console keyboard. + Note that the system administrator can configure the + reaction to ctrl-alt-del to be something else instead, + e.g., to be ignored, if the system is in a public + location. (Or to start nethack.) +

sysinit

Command to be run when the system is booted. This command + usually cleans up /tmp, for example. +

+ + The list above is not exhaustive. See your + inittab manual page for all possibilities, + and for details on how to use the above ones.

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Run levelsUpBooting in single user mode
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Booting in single user mode

An important run level is single user mode (run level 1), + in which only the system administrator is using the machine + and as few system services, including logins, as possible are + running. Single user mode is necessary for a few administrative + tasks, + + [1] + + such as running fsck on a + /usr partition, since this requires that + the partition be unmounted, and that can't happen, unless just + about all system services are killed.

A running system can be taken to single user mode by using + telinit to request run level 1. At bootup, + it can be entered by giving the word single + or emergency on the kernel command line: the + kernel gives the command line to init as well, + and init understands from that word that it + shouldn't use the default run level. (The kernel command line is + entered in a way that depends on how you boot the system.)

Booting into single user mode is sometimes necessary so + that one can run fsck by hand, before anything + mounts or otherwise touches a broken /usr + partition (any activity on a broken filesystem is likely to + break it more, so fsck should be run as soon + as possible).

The bootup scripts init runs + will automatically enter single user mode, if the automatic + fsck at bootup fails. This is an attempt to + prevent the system from using a filesystem that is so broken that + fsck can't fix it automatically. Such breakage + is relatively rare, and usually involves a broken hard disk or an + experimental kernel release, but it's good to be prepared.

As a security measure, a properly configured system + will ask for the root password before starting the shell in + single user mode. Otherwise, it would be simple to just enter + a suitable line to LILO to get in as root. (This will break if + /etc/passwd has been broken by filesystem + problems, of course, and in that case you'd better have a boot + floppy handy.)

Notes

[1]

It probably shouldn't be used for playing + nethack.

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Special configuration in /etc/inittabUpLogging In And Out
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Logins via the network

Two computers in the same network are usually linked via a + single physical cable. When they communicate over the network, + the programs in each computer that take part in the communication + are linked via a virtual connection, a sort + of imaginary cable. As far as the programs at either end of the + virtual connection are concerned, they have a monopoly on their + own cable. However, since the cable is not real, only imaginary, + the operating systems of both computers can have several virtual + connections share the same physical cable. This way, using just + a single cable, several programs can communicate without having + to know of or care about the other communications. It is even + possible to have several computers use the same cable; the virtual + connections exist between two computers, and the other computers + ignore those connections that they don't take part in.

That's a complicated and over-abstracted description of + the reality. It might, however, be good enough to understand + the important reason why network logins are somewhat different + from normal logins. The virtual connections are established + when there are two programs on different computers that wish + to communicate. Since it is in principle possible to login + from any computer in a network to any other computer, there is + a huge number of potential virtual communications. Because of + this, it is not practical to start a getty + for each potential login.

There is a single process inetd (corresponding to + getty) that handles all network logins. + When it notices an incoming network login (i.e., it notices + that it gets a new virtual connection to some other computer), + it starts a new process to handle that single login. The original + process remains and continues to listen for new logins.

To make things a bit more complicated, there is + more than one communication protocol for network logins. + The two most important ones are telnet and + rlogin. In addition to logins, there are many + other virtual connections that may be made (for FTP, Gopher, HTTP, + and other network services). It would be ineffective to have a + separate process listening for a particular type of connection, + so instead there is only one listener that can recognize the type + of the connection and can start the correct type of program to + provide the service. This single listener is called \cmd{inetd}; + see the Linux Network Administrators' Guide + for more information.

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Logging In And OutUpWhat login does
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What login does

The login program takes care of + authenticating the user (making sure that the username and + password match), and of setting up an initial environment for + the user by setting permissions for the serial line and starting + the shell.

Part of the initial setup is outputting the contents of + the file /etc/motd (short for message of the + day) and checking for electronic mail. These can be disabled + by creating a file called .hushlogin in + the user's home directory.

If the file /etc/nologin + exists, logins are disabled. That file is typically + created by shutdown and relatives. + login checks for this file, and will + refuse to accept a login if it exists. If it does exist, + login outputs its contents to the terminal + before it quits.

login logs all failed login attempts in + a system log file (via syslog). It also logs + all logins by root. Both of these can be useful when tracking + down intruders.

Currently logged in people are listed in + /var/run/utmp. This file is valid only + until the system is next rebooted or shut down; it is cleared + when the system is booted. It lists each user and the terminal + (or network connection) he is using, along with some other useful + information. The who, w, + and other similar commands look in utmp + to see who are logged in.

All successful logins are recorded into + /var/log/wtmp. This file will grow without + limit, so it must be cleaned regularly, for example by having + a weekly cron job to clear it. + + [1] + + The last command browses + wtmp.

Both utmp and + wtmp are in a binary format (see the + utmp manual page); it is unfortunately not + convenient to examine them without special programs.

Notes

[1]

Good Linux distributions do this out + of the box.

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Logins via the networkUpX and xdm
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X and xdm

XXX X implements logins via xdm; also: xterm -ls

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What login doesUpAccess control
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Access control

The user database is traditionally contained in the + /etc/passwd file. Some systems use + shadow passwords, and have moved the + passwords to /etc/shadow. Sites with many + computers that share the accounts use NIS or some other method + to store the user database; they might also automatically copy + the database from one central location to all other computers. +

The user database contains not only the passwords, but + also some additional information about the users, such as their + real names, home directories, and login shells. This other + information needs to be public, so that anyone can read it. + Therefore the password is stored encrypted. This does have + the drawback that anyone with access to the encrypted password + can use various cryptographical methods to guess it, without + trying to actually log into the computer. Shadow passwords try + to avoid this by moving the password into another file, which + only root can read (the password is still stored encrypted). + However, installing shadow passwords later onto a system that + did not support them can be difficult.

With or without passwords, it is important to make + sure that all passwords in a system are good, i.e., not easily + guessable. The crack program can be used + to crack passwords; any password it can find is by definition + not a good one. While crack can be run + by intruders, it can also be run by the system adminstrator + to avoid bad passwords. Good passwords can also be enforced + by the passwd program; this is in fact more + effective in CPU cycles, since cracking passwords requires quite + a lot of computation.

The user group database is kept in + /etc/group; for systems with shadow + passwords, there can be a /etc/shadow.group. +

root usually can't login via most terminals + or the network, only via terminals listed in the + /etc/securetty file. This makes it necessary + to get physical access to one of these terminals. It is, however, + possible to log in via any terminal as any other user, and use + the su command to become root.

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X and xdmUpShell startup
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Shell startup

When an interactive login shell starts, it automatically + executes one or more pre-defined files. Different shells execute + different files; see the documentation of each shell for further + information.

Most shells first run some global file, for example, the + Bourne shell (/bin/sh) and its derivatives + execute /etc/profile; in addition, + they execute .profile in the user's + home directory. /etc/profile allows the + system administrator to have set up a common user environment, + especially by setting the PATH to include local + command directories in addition to the normal ones. On the other + hand, .profile allows the user to customize + the environment to his own tastes by overriding, if necessary, + the default environment.

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Access controlUpManaging user accounts
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Creating a user

The Linux kernel itself treats users are mere numbers. + Each user is identified by a unique integer, the user + id or uid, because numbers are + faster and easier for a computer to process than textual names. + A separate database outside the kernel assigns a textual name, + the username, to each user id. The database + contains additional information as well.

To create a user, you need to add information about + the user to the user database, and create a home directory for + him. It may also be necessary to educate the user, and set up + a suitable initial environment for him.

Most Linux distributions come with a program for + creating accounts. There are several such programs available. + Two command line alternatives are adduser + and useradd; there may be a GUI tool as well. + Whatever the program, the result is that there is little if + any manual work to be done. Even if the details are many and + intricate, these programs make everything seem trivial. However, + the section called Creating a user by hand describes how to do it by hand. +

/etc/passwd and other informative files

The basic user database in a Unix system is the text file, + /etc/passwd (called the password + file), which lists all valid usernames and their + associated information. The file has one line per username, + and is divided into seven colon-delimited fields: + +

  • Username.

  • Password, in an encrypted form.

  • Numeric user id.

  • Numeric group id.

  • Full name or other description of account.

  • Home directory.

  • Login shell (program to run at login).

+ + The format is explained in more detail on the + passwd manual page.

Any user on the system may read the password file, + so that they can, for example, learn the name of another user. + This means that the password (the second field) is also available + to everyone. The password file encrypts the password, so in + theory there is no problem. However, the encryption is breakable, + especially if the password is weak (e.g., it is short or it can + be found in a dictionary). Therefore it is not a good idea to + have the password in the password file.

Many Linux systems have shadow passwords. This is + an alternative way of storing the password: the encrypted + password is stored in a separate file, /etc/shadow, + which only root can read. The /etc/passwd + file only contains a special marker in the second field. + Any program that needs to verify a user is setuid, and + can therefore access the shadow password file. Normal + programs, which only use the other fields in the password + file, can't get at the password. + + [1] + +

Picking numeric user and group ids

On most systems it doesn't matter what the numeric user + and group ids are, but if you use the Network filesystem (NFS), + you need to have the same uid and gid on all systems. This + is because NFS also identifies users with the numeric uids. + If you aren't using NFS, you can let your account creation tool + pick them automatically.

If you are using NFS, you'll have to be invent a mechanism + for synchronizing account information. One alternative is to + the NIS system (see XXX network-admin-guide).

However, you should try to avoid re-using numeric uid's + (and textual usernames), because the new owner of the uid (or + username) may get access to the old owner's files (or mail, + or whatever).

Initial environment: /etc/skel

When the home directory for a new user is created, it is + initialized with files from the /etc/skel + directory. The system administrator can create files in + /etc/skel that will provide a nice + default environment for users. For example, he might create a + /etc/skel/.profile that sets the EDITOR + environment variable to some editor that is friendly towards + new users.

However, it is usually best to try to keep + /etc/skel as small as possible, since it + will be next to impossible to update existing users' files. For + example, if the name of the friendly editor changes, all existing + users would have to edit their .profile. The + system administrator could try to do it automatically, with a + script, but that is almost certain going to break someone's file. +

Whenever possible, it is better to put global configuration + into global files, such as /etc/profile. This + way it is possible to update it without breaking users' + own setups.

Creating a user by hand

To create a new account manually, follow these steps: + + +

  • Edit /etc/passwd with + vipw and add a new line for the new account. Be + careful with the syntax. Do not edit directly with an + editor! vipw locks the file, so + that other commands won't try to update it at the same time. You + should make the password field be `*', so + that it is impossible to log in.

  • Similarly, edit /etc/group + with vigr, if you need to create a new group + as well.

  • Create the home directory of the user with + mkdir.

  • Copy the files from + /etc/skel to the new home directory. +

  • Fix ownerships and permissions with + chown and chmod. The + -R option is most useful. The correct + permissions vary a little from one site to another, but usually + the following commands do the right thing: + +

    cd /home/newusername
+chown -R username.group .
+chmod -R go=u,go-w .
+chmod go= .
    + +

  • Set the password with passwd. +

+

After you set the password in the last step, the account + will work. You shouldn't set it until everything else has been + done, otherwise the user may inadvertently log in while you're + still copying the files.

It is sometimes necessary to create dummy + accounts + + [2] + + that are not used by people. For example, to set up an anonymous + FTP server (so that anyone can download files from it, without + having to get an account first), you need to create an account + called ftp. In such cases, it is usually not necessary to set + the password (last step above). Indeed, it is better not to, so + that no-one can use the account, unless they first become root, + since root can become any user.

Notes

[1]

Yes, this means that the + password file has all the information about a user + except his password. The wonder + of development.

[2]

Surreal users?

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Managing user accountsUpChanging user properties
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Changing user properties

There are a few commands for changing various + properties of an account (i.e., the relevant field + in /etc/passwd): + +

chfn

Change the full name field. +

chsh

Change the login shell. +

passwd

Change the password. +

+ + The super-user may use these commands to change the properties + of any account. Normal users can only change the properties + of their own account. It may sometimes be necessary to disable + these commands (with chmod) for normal users, + for example in an environment with many novice users.

Other tasks need to be done by hand. For example, to + change the username, you need to edit /etc/passwd + directly (with vipw, remember). Likewise, to add + or remove the user to more groups, you need to edit + /etc/group (with vigr). Such tasks tend to + be rare, however, and should be done with caution: for + example, if + you change the username, e-mail will no longer reach the + user, unless you also create a mail alias. + + [1] + +

Notes

[1]

The user's name might change due to + marriage, for example, and he might want to have his + username reflect his new name.}

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Creating a userUpRemoving a user
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Removing a user

To remove a user, you first remove all + his files, mailboxes, mail aliases, print jobs, + cron and at jobs, + and all other references to the user. Then you remove the + relevant lines from /etc/passwd and + /etc/group (remember to remove the username + from all groups it's been added to). It may be a good idea to + first disable the account (see below), before you start removing + stuff, to prevent the user from using the account while it is + being removed.

Remember that users may have files outside their home + directory. The find command can find them: + +

find / -user username
+ + However, note that the above command will take a + long time, if you have large disks. If you + mount network disks, you need to be careful so that you won't + trash the network or the server.

Some Linux distributions come with special + commands to do this; look for deluser or + userdel. However, it is easy to do it by + hand as well, and the commands might not do everything.

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Changing user propertiesUpDisabling a user temporarily
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Disabling a user temporarily

It is sometimes necessary to temporarily disable an + account, without removing it. For example, the user might not + have paid his fees, or the system administrator may suspect that + a cracker has got the password of that account.

The best way to disable an account is to change its shell + into a special program that just prints a message. This way, + whoever tries to log into the account, will fail, and will + know why. The message can tell the user to contact the system + administrator so that any problems may be dealt with.

It would also be possible to change the username + or password to something else, but then the user + won't know what is going on. Confused users mean more + work. + + [1] + +

A simple way to create the special programs is to write + `tail scripts': + +

#!/usr/bin/tail +2
+This account has been closed due to a security breach.
+Please call 555-1234 and wait for the men in black to arrive.
+ + The first two characters (`#!') tell the + kernel that the rest of the line is a command that needs to be + run to interpret this file. The tail command + in this case outputs everything except the first line to the + standard output.

If user billg is suspected of a security breach, + the system administrator would do something like this: + +

# chsh -s /usr/local/lib/no-login/security billg
+# su - tester
+This account has been closed due to a security breach.
+Please call 555-1234 and wait for the men in black to arrive.
+#
+ + The purpose of the su is to test that the + change worked, of course.

Tail scripts should be kept in a separate directory, + so that their names don't interfere with normal user commands. +

Notes

[1]

But they can be so + fun, if you're a BOFH.

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Removing a userUpBackups
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Selecting the backup medium

The most important decision regarding backups is the choice + of backup medium. You need to consider cost, reliability, speed, + availability, and usability.

Cost is important, since you should preferably have + several times more backup storage than what you need for the data. + A cheap medium is usually a must.

Reliability is extremely important, since a broken + backup can make a grown man cry. A backup medium must be able + to hold data without corruption for years. The way you use the + medium affects it reliability as a backup medium. A hard disk + is typically very reliable, but as a backup medium it is not + very reliable, if it is in the same computer as the disk you + are backing up.

Speed is usually not very important, if backups can be done + without interaction. It doesn't matter if a backup takes two + hours, as long as it needs no supervision. On the other hand, + if the backup can't be done when the computer would otherwise + be idle, then speed is an issue.

Availability is obviously necessary, since you can't + use a backup medium if it doesn't exist. Less obvious is the + need for the medium to be available even in the future, and on + computers other than your own. Otherwise you may not be able + to restore your backups after a disaster.

Usability is a large factor in how often backups are made. + The easier it is to make backups, the better. A backup medium + mustn't be hard or boring to use.

The typical alternatives are floppies and tapes. + Floppies are very cheap, fairly reliable, not very fast, + very available, but not very usable for large amounts of data. + Tapes are cheap to somewhat expensive, fairly reliable, fairly + fast, quite available, and, depending on the size of the tape, + quite comfortable.

There are other alternatives. They are usually not very + good on availability, but if that is not a problem, they can + be better in other ways. For example, magneto-optical disks + can have good sides of both floppies (they're random access, + making restoration of a single file quick) and tapes (contain + a lot of data).

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BackupsUpSelecting the backup tool
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Selecting the backup tool

There are many tools that can be used to make + backups. The traditional UNIX tools used for backups + are tar, cpio, and + dump. In addition, there are large number + of third party packages (both freeware and commercial) that + can be used. The choice of backup medium can affect the choice + of tool.

tar and cpio are + similar, and mostly equivalent from a backup point of view. + Both are capable of storing files on tapes, and retrieving + files from them. Both are capable of using almost any media, + since the kernel device drivers take care of the low level + device handling and the devices all tend to look alike to user + level programs. Some UNIX versions of tar + and cpio may have problems with unusual files + (symbolic links, device files, files with very long pathnames, and + so on), but the Linux versions should handle all files correctly. +

dump is different in that it reads + the filesystem directly and not via the filesystem. It is + also written specifically for backups; tar + and cpio are really for archiving files, + although they work for backups as well.

Reading the filesystem directly has some advantages. + It makes it possible to back files up without affecting their time + stamps; for tar and cpio, + you would have to mount the filesystem read-only first. + Directly reading the filesystem is also more effective, if + everything needs to be backed up, since it can be done with + much less disk head movement. The major disadvantage is that + it makes the backup program specific to one filesystem type; + the Linux dump program understands the ext2 + filesystem only.

dump also directly supports + backup levels (which we'll be discussing below); with + tar and cpio this has to + be implemented with other tools.

A comparison of the third party backup tools is beyond + the scope of this book. The Linux Software Map lists many of + the freeware ones.

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Selecting the backup mediumUpSimple backups
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Simple backups

A simple backup scheme is to back up everything once, + then back up everything that has been modified since the + previous backup. The first backup is called a full + backup, the subsequent ones are incremental + backups. A full backup is often more laborius + than incremental ones, since there is more data to write to the + tape and a full backup might not fit onto one tape (or floppy). + Restoring from incremental backups can be many times more work + than from a full one. Restoration can be optimized so that + you always back up everything since the previous full backup; + this way, backups are a bit more work, but there should never + be a need to restore more than a full backup and an incremental + backup.

If you want to make backups every day and have six + tapes, you could use tape~1 for the first full backup (say, on + a Friday), and tapes 2 to 5 for the incremental backups (Monday + through Thursday). Then you make a new full backup on tape 6 + (second Friday), and start doing incremental ones with tapes 2 + to 5 again. You don't want to overwrite tape 1 until you've got + a new full backup, lest something happens while you're making + the full backup. After you've made a full backup to tape 6, + you want to keep tape 1 somewhere else, so that when your other + backup tapes are destroyed in the fire, you still have at least + something left. When you need to make the next full backup, + you fetch tape 1 and leave tape 6 in its place.

If you have more than six tapes, you can use the extra + ones for full backups. Each time you make a full backup, you + use the oldest tape. This way you can have full backups from + several previous weeks, which is good if you want to find an old, + now deleted file, or an old version of a file.

Making backups with tar

A full backup can easily be made with tar: + +

# tar --create --file /dev/ftape /usr/src
+tar: Removing leading / from absolute path names in the archive
+#
+ + The example above uses the GNU version of tar + and its long option names. The traditional version of + tar only understands single character + options. The GNU version can also handle backups that don't + fit on one tape or floppy, and also very long paths; not all + traditional versions can do these things. (Linux only uses + GNU tar.)

If your backup doesn't fit on one tape, you need to use + the --multi-volume (-M) option: + +

# tar -cMf /dev/fd0H1440 /usr/src
+tar: Removing leading / from absolute path names in the archive
+Prepare volume \#2 for /dev/fd0H1440 and hit return:
+#
+ + Note that you should format the floppies before you begin the + backup, or else use another window or virtual terminal and do + it when tar asks for a new floppy.

After you've made a backup, you should check that it is OK, + using the --compare (-d) option: + +

# tar --compare --verbose -f /dev/ftape
+usr/src/
+usr/src/linux
+usr/src/linux-1.2.10-includes/
+....
+#
+ + Failing to check a backup means that you will not notice that your + backups aren't working until after you've lost the original data. +

An incremental backup can be done with + tar using the --newer + (-N) option: + +

# tar --create --newer '8 Sep 1995' --file /dev/ftape /usr/src --verbose
+tar: Removing leading / from absolute path names in the archive
+usr/src/
+usr/src/linux-1.2.10-includes/
+usr/src/linux-1.2.10-includes/include/
+usr/src/linux-1.2.10-includes/include/linux/
+usr/src/linux-1.2.10-includes/include/linux/modules/
+usr/src/linux-1.2.10-includes/include/asm-generic/
+usr/src/linux-1.2.10-includes/include/asm-i386/
+usr/src/linux-1.2.10-includes/include/asm-mips/
+usr/src/linux-1.2.10-includes/include/asm-alpha/
+usr/src/linux-1.2.10-includes/include/asm-m68k/
+usr/src/linux-1.2.10-includes/include/asm-sparc/
+usr/src/patch-1.2.11.gz
+#
+ + Unfortunately, tar can't notice when a file's + inode information has changed, for example, that it's permission + bits have been changed, or when its name has been changed. + This can be worked around using find and + comparing current filesystem state with lists of files that have + been previously backed up. Scripts and programs for doing this + can be found on Linux ftp sites.

Restoring files with tar

The --extract (-x) + option for tar extracts files: + +

# tar --extract --same-permissions --verbose --file /dev/fd0H1440
+usr/src/
+usr/src/linux
+usr/src/linux-1.2.10-includes/
+usr/src/linux-1.2.10-includes/include/
+usr/src/linux-1.2.10-includes/include/linux/
+usr/src/linux-1.2.10-includes/include/linux/hdreg.h
+usr/src/linux-1.2.10-includes/include/linux/kernel.h
+...
+#
+ + You also extract only specific files or directories (which + includes all their files and subdirectories) by naming on the + command line: + +
# tar xpvf /dev/fd0H1440 usr/src/linux-1.2.10-includes/include/linux/hdreg.h
+usr/src/linux-1.2.10-includes/include/linux/hdreg.h
+#
+ + Use the --list (-t) option, + if you just want to see what files are on a backup volume: + +
# tar --list --file /dev/fd0H1440
+usr/src/
+usr/src/linux
+usr/src/linux-1.2.10-includes/
+usr/src/linux-1.2.10-includes/include/
+usr/src/linux-1.2.10-includes/include/linux/
+usr/src/linux-1.2.10-includes/include/linux/hdreg.h
+usr/src/linux-1.2.10-includes/include/linux/kernel.h
+...
+#
+ + Note that tar always reads the backup volume + sequentially, so for large volumes it is rather slow. It is not + possible, however, to use random access database techniques when + using a tape drive or some other sequential medium.

tar doesn't handle deleted files + properly. If you need to restore a filesystem from a full and + an incremental backup, and you have deleted a file between + the two backups, it will exist again after you have done the + restore. This can be a big problem, if the file has sensitive + data that should no longer be available.

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Selecting the backup toolUpMultilevel backups
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Multilevel backups

The simple backup method outlined in the previous section + is often quite adequate for personal use or small sites. For more + heavy duty use, multilevel backups are more appropriate.

The simple method has two backup levels: full and + incremental backups. This can be generalized to any number of + levels. A full backup would be level 0, and the different levels + of incremental backups levels 1, 2, 3, etc. At each incremental + backup level you back up everything that has changed since the + previous backup at the same or a previous level.

The purpose for doing this is that it allows a longer + backup history cheaply. In the example in + the previous section, the backup history went back to the previous + full backup. This could be extended by having more tapes, but + only a week per new tape, which might be too expensive. A longer + backup history is useful, since deleted or corrupted files are + often not noticed for a long time. Even a version of a file that + is not very up to date is better than no file at all.

With multiple levels the backup history can be extended + more cheaply. For example, if we buy ten tapes, we could use + tapes 1 and 2 for monthly backups (first Friday each month), + tapes 3 to 6 for weekly backups (other Fridays; note that there + can be five Fridays in one month, so we need four more tapes), + and tapes 7 to 10 for daily backups (Monday to Thursday). + With only four more tapes, we've been able to extend the backup + history from two weeks (after all daily tapes have been used) + to two months. It is true that we can't restore every version + of each file during those two months, but what we can restore + is often good enough.

Figure 10-1 shows which backup + level is used each day, and which backups can be restored from + at the end of the month.

Figure 10-1. A sample multilevel backup schedule.

Backup levels can also be used to keep filesystem + restoration time to a minimum. If you have many incremental + backups with monotonously growing level numbers, you need to + restore all of them if you need to rebuild the whole filesystem. + Instead you can use level numbers that aren't monotonous, and + keep down the number of backups to restore.

To minimize the number of tapes needed to restore, you + could use a smaller level for each incremental tape. However, + then the time to make the backups increases (each backup copies + everything since the previous full backup). A better scheme is + suggested by the dump manual page and described + by the table XX (efficient-backup-levels). Use the following + succession of backup levels: 3, 2, 5, 4, 7, 6, 9, 8, 9, etc. + This keeps both the backup and restore times low. The most you + have to backup is two day's worth of work. The number of tapes + for a restore depends on how long you keep between full backups, + but it is less than in the simple schemes.

Table 10-1. Efficient backup scheme using many backup levels

TapeLevelBackup (days)Restore tapes
10n/a1
2311, 2
3221, 3
4511, 2, 4
5421, 2, 5
6711, 2, 5, 6
7621, 2, 5, 7
8911, 2, 5, 7, 8
9821, 2, 5, 7, 9
10911, 2, 5, 7, 9, 10
11911, 2, 5, 7, 9, 10, 11
...911, 2, 5, 7, 9, 10, 11, ...

A fancy scheme can reduce the amount of labor needed, but + it does mean there are more things to keep track of. You must + decide if it is worth it.

dump has built-in support for backup + levels. For tar and cpio + it must be implemented with shell scripts.

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What to back up

You want to back up as much as possible. The major + exception is software that can be easily reinstalled, + + [1] + + but even they may have configuration files that it is + important to back up, lest you need to do all the work to + configure them all over again. Another major exception is + the /proc filesystem; since that only + contains data that the kernel always generates automatically, + it is never a good idea to back it up. Expecially the + /proc/kcore file is unnecessary, since it + is just an image of your current physical memory; it's pretty + large as well.

Gray areas include the news spool, log files, and many + other things in /var. You must decide what + you consider important.

The obvious things to back up are user files + (/home) and system configuration files + (/etc, but possibly other things scattered + all over the filesystem).

Notes

[1]

You get to decide what's easy. + Some people consider installing from dozens of floppies + easy.

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Multilevel backupsUpCompressed backups
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Compressed backups

Backups take a lot of space, which can cost quite + a lot of money. To reduce the space needed, the backups + can be compressed. There are several ways of doing this. + Some programs have support for for compression built in; for + example, the --gzip (-z) + option for GNU tar pipes the whole backup + through the gzip compression program, before + writing it to the backup medium.

Unfortunately, compressed backups can cause trouble. + Due to the nature of how compression works, if a single bit is + wrong, all the rest of the compressed data will be unusable. + Some backup programs have some built in error correction, but no + method can handle a large number of errors. This means that if + the backup is compressed the way GNU tar does + it, with the whole output compressed as a unit, a single error + makes all the rest of the backup lost. Backups must be reliable, + and this method of compression is not a good idea.

An alternative way is to compress each file separately. + This still means that the one file is lost, but all other files + are unharmed. The lost file would have been corrupted anyway, + so this situation is not much worse than not using compression + at all. The afio program (a variant of + cpio) can do this.

Compression takes some time, which may make the backup program + unable to write data fast enough for a tape drive. + + [1] + + This can be avoided by buffering the output (either internally, if + the backup program if smart enough, or by using another program), + but even that might not work well enough. This should only be + a problem on slow computers.

Notes

[1]

If a tape drive doesn't data fast enough, + it has to stop; this makes backups even slower, and can + be bad for the tape and the drive.

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What to back upUpKeeping Time
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The hardware and software clocks

A personal computer has a battery driven hardware clock. + The battery ensures that the clock will work even if the rest of + the computer is without electricity. The hardware clock can be + set from the BIOS setup screen or from whatever operating system + is running.

The Linux kernel keeps track of time independently from + the hardware clock. During the boot, Linux sets its own clock + to the same time as the hardware clock. After this, both clocks + run independently. Linux maintains its own clock because looking + at the hardware is slow and complicated.

The kernel clock always shows universal time. This way, + the kernel does not need to know about time zones at all. The + simplicity results in higher reliability and makes it easier + to update the time zone information. Each process handles time + zone conversions itself (using standard tools that are part of + the time zone package).

The hardware clock can be in local time or in universal + time. It is usually better to have it in universal time, + because then you don't need to change the hardware clock when + daylight savings time begins or ends (UTC does not have DST). + Unfortunately, some PC operating systems, including MS-DOS, + Windows, and OS/2, assume the hardware clock shows local time. + Linux can handle either, but if the hardware clock shows local + time, then it must be modified when daylight savings time begins + or ends (otherwise it wouldn't show local time).

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Keeping TimeUpShowing and setting time
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Showing and setting time

In the Debian system, the system time zone is determined + by the symbolic link /etc/localtime. + This link points at a time zone data file that describes + the local time zone. The time zone data files are stored in + /usr/lib/zoneinfo. Other Linux distributions + may do this differently.

A user can change his private time zone by setting the + TZ environment variable. If it is unset, the system time zone + is assumed. The syntax of the TZ variable is described in the + tzset manual page.

The date command shows the current date and + time. + + [1] + + For example: + +

$ date
+Sun Jul 14 21:53:41 EET DST 1996
+$
+ + That time is Sunday, 14th of July, 1996, at about ten before + ten at the evening, in the time zone called ``EET DST'' + (which might be East European Daylight Savings Time). + date can also show the univeral time: + +
$ date -u
+Sun Jul 14 18:53:42 UTC 1996
+Sun Jul 14 18:53:42 UTC 1996
+$
+ + date is also used to set the kernel's software + clock: + +
# date 07142157
+Sun Jul 14 21:57:00 EET DST 1996
+# date
+Sun Jul 14 21:57:02 EET DST 1996
+#
+ + See the date manual page for more details; + the syntax is a bit arcane. Only root can set the time. + While each user can have his own time zone, the clock is the + same for everyone.

date only shows or sets the software + clock. The clock commands syncronizes + the hardware and software clocks. It is used when the system + boots, to read the hardware clock and set the software clock. + If you need to set both clocks, you first set the software clock + with date, and then the hardware clock with + clock -w.

The -u option to clock + tells it that the hardware clock is in universal time. + You must use the -u + option correctly. If you don't, your computer will be quite + confused about what the time is.

The clocks should be changed with care. Many parts of a + Unix system require the clocks to work correctly. For example, + the cron daemon runs commands periodically. + If you change the clock, it can be confused of whether + it needs to run the commands or not. On one early Unix + system, someone set the clock twenty years into the future, + and cron wanted to run all the periodic + commands for twenty years all at once. Current versions of + cron can handle this correctly, but you should + still be careful. Big jumps or backward jumps are more dangeours + than smaller or forward ones.

Notes

[1]

Beware of the time command, which does + not show the current time.

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The hardware and software clocksUpWhen the clock is wrong
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When the clock is wrong

The Linux software clock is not always accurate. It is + kept running by a periodic timer interrupt + generated by PC hardware. If the system has too many processes + running, it may take too long to service the timer interrupt, and + the software clock starts slipping behind. The hardware clock + runs independently and is usually more accurate. If you boot + your computer often (as is the case for most systems that aren't + servers), it will usually keep fairly accurate time.

If you need to adjust the hardware clock, it is usually + simplest to reboot, go into the BIOS setup screen, and do it + from there. This avoids all trouble that changing system time + might cause. If doing it via BIOS is not an option, set the new + time with date and clock + (in that order), but be prepared to reboot, if some part of the + system starts acting funny.

A networked computer (even if just over the modem) can + check its own clock automatically, by comparing it to some other + computer's time. If the other computer is known to keep very + accurate time, then both computers will keep accurate time. + This can be done by using the rdate and + netdate commands. Both check the time of a + remote computer (netdate can handle several + remote computers), and set the local computer's time to that. + By running one these commands regularly, your computer will keep + as accurate time as the remote computer.

XXX say something intelligent about NTP

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Showing and setting timeUpGlossary (DRAFT)
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The root filesystem

The root filesystem should generally be small, since + it contains very critical files and a small, infrequently + modified filesystem has a better chance of not getting corrupted. + A corrupted root filesystem will generally mean that the system + becomes unbootable except with special measures (e.g., from a + floppy), so you don't want to risk it.

The root directory generally doesn't contain any files, except + perhaps the standard boot image for the system, usually called + /vmlinuz. All other files are in subdirectories in the + root filesystems: + +

/bin

Commands needed during bootup + that might be used by normal users (probably after + bootup).

/sbin

Like /bin, + but the commands are not intended for normal + users, although they may use them if necessary and + allowed.

/etc

Configuration files specific to the + machine.

/root

The home directory for user + \texttt{root}.

/lib

Shared libraries needed by the programs + on the root filesystem.

/lib/modules

Loadable kernel modules, especially + those that are needed to boot the system when + recovering from disasters (e.g., network and filesystem + drivers).

/dev

Device files.

/tmp

Temporary files. Programs running after + bootup should use /var/tmp, not + /tmp, since the former is probably + on a disk with more space.

/boot

Files used by the bootstrap loader, + e.g., LILO. Kernel images are often kept here instead + of in the root directory. If there are many kernel + images, the directory can easily grow rather big, and it + might be better to keep it in a separate filesystem. + Another reason would be to make sure the kernel + images are within the first 1024 cylinders of an IDE + disk.

/mnt

Mount point for temporary mounts by + the system administrator. Programs aren't supposed + to mount on /mnt automatically. + /mnt might be divided into + subdirectories (e.g., /mnt/dosa + might be the floppy drive using an MS-DOS filesystem, + and /mnt/exta might be the same + with an ext2 filesystem).

/proc, /usr, /var, /home

Mount points for the other + filesystems.

+

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Overview of the Directory TreeUpThe /etc directory
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The /etc directory

The /etc directory contains a lot + of files. Some of them are described below. For others, you + should determine which program they belong to and read the manual + page for that program. Many networking configuration files are + in /etc as well, and are described in the + Networking Administrators' Guide. + +

/etc/rc or /etc/rc.d or /etc/rc?.d

Scripts or directories of scripts + to run at startup or when changing the run level. + See the chapter on init for further + information.

/etc/passwd

The user database, with fields giving + the username, real name, home directory, encrypted + password, and other information about each user. + The format is documented in the \man{passwd} manual page. +

/etc/fdprm

Floppy disk parameter table. + Describes what different floppy disk formats look + like. Used by setfdprm. See the + setfdprm manual page for more + information.

/etc/fstab

Lists the filesystems mounted + automatically at startup by the mount + -a command (in /etc/rc + or equivalent startup file). Under Linux, also contains + information about swap areas used automatically by + swapon -a. See the section called Mounting and unmounting in Chapter 4 and the + mount manual page for more information. +

/etc/group

Similar to + /etc/passwd, but + describes groups instead of users. See the + group manual page for more information. +

/etc/inittab

Configuration file for + init.

/etc/issue

Output by getty before + the login prompt. Usually contains a short description or + welcoming message to the system. The contents are up to + the system administrator.

/etc/magic

The configuration file + for file. Contains the + descriptions of various file formats based on + which file guesses the type of + the file. See the magic and + file manual pages for more information. +

/etc/motd

The message of the day, automatically + output after a successful login. Contents are up to the + system administrator. Often used for getting information + to every user, such as warnings about planned downtimes. +

/etc/mtab

List of currently mounted filesystems. + Initially set up by the bootup scripts, and updated + automatically by the mount + command. Used when a list of mounted filesystems is + needed, e.g., by the df command. +

/etc/shadow

Shadow password file on systems + with shadow password software installed. + Shadow passwords move the encrypted password + from /etc/passwd into + /etc/shadow; the latter is not + readable by anyone except root. This makes it harder + to crack passwords.

/etc/login.defs

Configuration file for + the login command. +

/etc/printcap

Like /etc/termcap, + but intended for printers. Different syntax. +

/etc/profile, /etc/csh.login, /etc/csh.cshrc

Files executed at login or startup time + by the Bourne or C shells. These allow the system + administrator to set global defaults for all users. + See the manual pages for the respective shells. +

/etc/securetty

Identifies secure terminals, i.e., + the terminals from which root is allowed to log in. + Typically only the virtual consoles are listed, so + that it becomes impossible (or at least harder) to gain + superuser privileges by breaking into a system over a + modem or a network.

/etc/shells

Lists trusted shells. The + chsh command allows users to change + their login shell only to shells listed in this file. + ftpd, the server process that provides + FTP services for a machine, will check that the user's + shell is listed in /etc/shells + and will not let people log in unles the shell is + listed there.

/etc/termcap

The terminal capability database. + Describes by what ``escape sequences'' various terminals + can be controlled. Programs are written so that instead + of directly outputting an escape sequence that only + works on a particular brand of terminal, they look up + the correct sequence to do whatever it is they want to + do in /etc/termcap. As a result + most programs work with most kinds of terminals. + See the termcap, curs_termcap, + and terminfo manual pages for + more information.

+

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The root filesystemUpThe /dev directory
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The /dev directory

The /dev directory contains + the special device files for all the devices. The device + files are named using special conventions; these are + described in the Device list (see + XXX). The device files are created during installation, + and later with the /dev/MAKEDEV script. + The /dev/MAKEDEV.local is a script written + by the system administrator that creates local-only device + files or links (i.e., those that are not part of the standard + MAKEDEV, such as device files for some + non-standard device driver).

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The /etc directoryUpThe /usr filesystem
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The /usr filesystem

The /usr filesystem is often + large, since all programs are installed there. All files + in /usr usually come from a Linux + distribution; locally installed programs and other stuff goes + below /usr/local. This makes it possible + to update the system from a new version of the distribution, + or even a completely new distribution, without having to + install all programs again. Some of the subdirectories of + /usr are listed below (some of the less + important directories have been dropped; see the FSSTND for + more information). + +

/usr/X11R6

The X Window System, all files. + To simplify the development and installation of + X, the X files have not been integrated into the + rest of the system. There is a directory tree + below /usr/X11R6 similar + to that below /usr itself. +

/usr/X386

Similar to + /usr/X11R6, but for X11 Release 5. +

/usr/bin

Almost all user commands. + Some commands are in /bin + or in /usr/local/bin. +

/usr/sbin

System administration commands that are + not needed on the root filesystem, e.g., most server + programs.

/usr/man, /usr/info, /usr/doc

Manual pages, GNU Info documents, and + miscellaneous other documentation files, respectively. +

/usr/include

Header files for the C + programming language. This should actually be below + /usr/lib for consistency, but the + tradition is overwhelmingly in support for this name. +

/usr/lib

Unchanging data files for programs and + subsystems, including some site-wide configuration + files. The name lib comes from library; + originally libraries of programming subroutines + were stored in /usr/lib. +

/usr/local

The place for locally installed software + and other files.

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The /dev directoryUpThe /var filesystem
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The /var filesystem

The /var contains data that is changed when the system is + running normally. It is specific for each system, i.e., not + shared over the network with other computers. + +

/var/catman

A cache for man pages that are formatted + on demand. The source for manual pages is usually + stored in /usr/man/man*; some + manual pages might come with a pre-formatted version, + which is stored in /usr/man/cat*. + Other manual pages need to be formatted when they are + first viewed; the formatted version is then stored + in /var/man so that the next + person to view the same page won't have to wait for + it to be formatted. (/var/catman + is often cleaned in the same way temporary directories + are cleaned.)

/var/lib

Files that change while the system is + running normally.

/var/local

Variable data for programs that are + installed in /usr/local (i.e., + programs that have been installed by the system + administrator). Note that even locally installed + programs should use the other /var + directories if they are appropriate, e.g., + /var/lock.

/var/lock

Lock files. Many programs + follow a convention to create a lock file in + /var/lock to indicate that they + are using a particular device or file. Other programs + will notice the lock file and won't attempt to use the + device or file.

/var/log

Log files from various + programs, especially login + (/var/log/wtmp, which logs all logins + and logouts into the system) and syslog + (/var/log/messages, where all + kernel and system program message are usually stored). + Files in /var/log can often grow + indefinitely, and may require cleaning at regular + intervals.

/var/run

Files that contain information about the + system that is valid until the system is next booted. + For example, /var/run/utmp + contains information about people currently logged + in.

/var/spool

Directories for mail, + news, printer queues, and other queued work. + Each different spool has its own subdirectory + below /var/spool, + e.g., the mailboxes of the users are in + /var/spool/mail.

/var/tmp

Temporary files that are large + or that need to exist for a longer time than + what is allowed for /tmp. + (Although the system administrator might not allow + very old files in /var/tmp + either.)

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The /usr filesystemUpThe /proc filesystem
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The /proc filesystem

The /proc filesystem contains + a illusionary filesystem. It does not exist on a disk. + Instead, the kernel creates it in memory. It is used to provide + information about the system (originally about processes, hence + the name). Some of the more important files and directories are + explained below. The /proc filesystem is + described in more detail in the proc manual page. + +

/proc/1

A directory with information about + process number 1. Each process has a directory below + /proc with the name being its process + identification number.

/proc/cpuinfo

Information about the processor, + such as its type, make, model, and perfomance. +

/proc/devices

List of device drivers configured into the + currently running kernel.

/proc/dma

Shows which DMA channels are being used + at the moment.

/proc/filesystems

Filesystems configured into the kernel. +

/proc/interrupts

Shows which interrupts are + in use, and how many of each there have been. +

/proc/ioports

Which I/O ports are in use at the moment. +

/proc/kcore

An image of the physical memory of + the system. This is exactly the same size as your + physical memory, but does not really take up that much + memory; it is generated on the fly as programs access it. + (Remember: unless you copy it elsewhere, nothing under + /proc takes up any disk space + at all.)

/proc/kmsg

Messages output by the kernel. + These are also routed to syslog. +

/proc/ksyms

Symbol table for the kernel. +

/proc/loadavg

The `load average' of the system; three + meaningless indicators of how much work the system has + to do at the moment.

/proc/meminfo

Information about memory usage, both + physical and swap.

/proc/modules

Which kernel modules are loaded at + the moment.

/proc/net

Status information about network + protocols.

/proc/self

A symbolic link to the process + directory of the program that is looking at + /proc. When two processes look at + /proc, they get different links. + This is mainly a convenience to make it easier + for programs to get at their process directory. +

/proc/stat

Various statistics about the system, such + as the number of page faults since the system was booted. +

/proc/uptime

The time the system has been up. +

/proc/version

The kernel version. +

Note that while the above files tend to be easily + readable text files, they can sometimes be formatted in a way + that is not easily digestable. There are many commands that + do little more than read the above files and format them for + easier understanding. For example, the free + program reads /proc/meminfo and converts + the amounts given in bytes to kilobytes (and adds a little more + information, as well).

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Hard disks

This subsection introduces terminology related to hard + disks. If you already know the terms and concepts, you can skip + this subsection.

See Figure 4-1 for a schematic picture + of the important parts in a hard disk. A hard disk consists of + one or more circular platters, + + [1] + + of which either or both surfaces are coated + with a magnetic substance used for recording the data. For each + surface, there is a read-write head that + examines or alters the recorded data. The platters rotate on + a common axis; a typical rotation speed is 3600 rotations per + minute, although high-performance hard disks have higher speeds. + The heads move along the radius of the platters; this movement + combined with the rotation of the platters allows the head to + access all parts of the surfaces.

The processor (CPU) and the actual disk communicate through + a disk controller. This relieves the rest of the computer + from knowing how to use the drive, since the controllers for + different types of disks can be made to use the same interface + towards the rest of the computer. Therefore, the computer can + say just ``hey disk, gimme what I want'', instead of a long and + complex series of electric signals to move the head to the proper + location and waiting for the correct position to come under + the head and doing all the other unpleasant stuff necessary. + (In reality, the interface to the controller is still complex, + but much less so than it would otherwise be.) The controller + can also do some other stuff, such as caching, or automatic bad + sector replacement.

The above is usually all one needs to understand about the + hardware. There is also a bunch of other stuff, such as the + motor that rotates the platters and moves the heads, and the + electronics that control the operation of the mechanical + parts, but that is mostly not relevant for understanding the + working principle of a hard disk.

The surfaces are usually divided into concentric rings, + called tracks, and these in turn are + divided into sectors. This division + is used to specify locations on the hard disk and to allocate + disk space to files. To find a given place on the hard disk, + one might say ``surface 3, track 5, sector 7''. Usually the + number of sectors is the same for all tracks, but some hard disks + put more sectors in outer tracks (all sectors are of the same + physical size, so more of them fit in the longer outer tracks). + Typically, a sector will hold 512 bytes of data. The disk itself + can't handle smaller amounts of data than one sector.

Figure 4-1. A schematic picture of a hard disk.

Each surface is divided into tracks (and sectors) in + the same way. This means that when the head for one surface + is on a track, the heads for the other surfaces are also on + the corresponding tracks. All the corresponding tracks taken + together are called a cylinder. It takes + time to move the heads from one track (cylinder) to another, + so by placing the data that is often accessed together (say, a + file) so that it is within one cylinder, it is not necessary to + move the heads to read all of it. This improves performance. + It is not always possible to place files like this; files + that are stored in several places on the disk are called + fragmented.

The number of surfaces (or heads, which is the same thing), + cylinders, and sectors vary a lot; the specification of the + number of each is called the geometry of a hard disk. The + geometry is usually stored in a special, battery-powered memory + location called the CMOS RAM, from where the operating + system can fetch it during bootup or driver initialization.

Unfortunately, the BIOS + + [2] + + has a design limitation, which makes it + impossible to specify a track number that is larger than 1024 in + the CMOS RAM, + which is too little for a large hard disk. To overcome this, + the hard disk controller lies about the geometry, and + translates the addresses given by the computer into something + that fits reality. For example, a hard disk might have 8 heads, + 2048 tracks, and 35 sectors per track. + + [3] + + Its controller could lie to the computer and claim that it + has 16 heads, 1024 tracks, and 35 sectors per track, thus not + exceeding the limit on tracks, and translates the address that + the computer gives it by halving the head number, and doubling + the track number. The math can be more complicated in reality, + because the numbers are not as nice as here (but again, the + details are not relevant for understanding the principle). + This translation distorts the operating system's view of how + the disk is organized, thus making it impractical to use the + all-data-on-one-cylinder trick to boost performance.

The translation is only a problem for IDE disks. SCSI disks + use a sequential sector number (i.e., the controller translates + a sequential sector number to a head, cylinder, and sector + triplet), and a completely different method for the CPU to talk + with the controller, so they are insulated from the problem. + Note, however, that the computer might not know the real geometry + of an SCSI disk either.

Since Linux often will not know the real geometry of a disk, + its filesystems don't even try to keep files within a single + cylinder. Instead, it tries to assign sequentially numbered + sectors to files, which almost always gives similar performance. + The issue is further complicated by on-controller caches, and + automatic prefetches done by the controller.

Each hard disk is represented by a separate device + file. There can (usually) be only two or four IDE hard + disks. These are known as /dev/hda, + /dev/hdb, /dev/hdc, + and /dev/hdd, respectively. SCSI + hard disks are known as /dev/sda, + /dev/sdb, and so on. Similar naming + conventions exist for other hard disk types; see XXX (device + list) for more information. Note that the device files for + the hard disks give access to the entire disk, with no regard + to partitions (which will be discussed below), and it's easy to + mess up the partitions or the data in them if you aren't careful. + The disks' device files are usually used only to get access to the + master boot record (which will also be discussed below).

Notes

[1]

The platters are made of a hard + substance, e.g., aluminium, which gives the hard disk + its name.

[2]

The BIOS is some built-in software stored on + ROM chips. It takes care, among other things, of the + initial stages of booting.

[3]

The numbers are completely + imaginary.

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Floppies

A floppy disk consists of a flexible membrane covered on one + or both sides with similar magnetic substance as a hard disk. + The floppy disk itself doesn't have a read-write head, that is + included in the drive. A floppy corresponds to one platter in + a hard disk, but is removable and one drive can be used to + access different floppies, whereas the hard disk is one + indivisible unit.

Like a hard disk, a floppy is divided into tracks and sectors + (and the two corresponding tracks on either side of a floppy + form a cylinder), but there are many fewer of them than on a + hard disk.

A floppy drive can usually use several different types of disks; + for example, a 3.5 inch drive can use both 720 kB and + 1.44 MB disks. Since the drive has to operate a bit differently + and the operating system must know how big the disk is, there + are many device files for floppy drives, one per combination of + drive and disk type. + Therefore, /dev/fd0H1440 is the first floppy drive (fd0), + which must be a 3.5 inch drive, + using a 3.5 inch, high density disk (H) of + size 1440 kB (1440), i.e., a normal 3.5 inch HD floppy. + For more information on the naming conventions for the floppy + devices, see XXX (device list).

The names for floppy drives are complex, however, and Linux + therefore has a special floppy device type that automatically + detects the type of the disk in the drive. It works by + trying to read the first sector of a newly inserted floppy + using different floppy types until it finds the correct one. + This naturally requires that the floppy is formatted first. + The automatic devices are called /dev/fd0, + /dev/fd1, and so on.

The parameters the automatic device uses to access a disk can + also be set using the program \cmd{setfdprm}. This can be + useful if you need to use disks that do not follow any usual + floppy sizes, e.g., if they have an unusual number of sectors, + or if the autodetecting for some reason fails and the proper + device file is missing.

Linux can handle many nonstandard floppy disk formats + in addition to all the standard ones. Some of these require + using special formatting programs. We'll skip these disk + types for now, but in the mean time you can examine the + /etc/fdprm file. It specifies the settings + that setfdprm recognizes.

The operating system must know when a disk has been changed in + a floppy drive, for example, in order to avoid using cached + data from the previous disk. Unfortunately, the signal line + that is used for this is sometimes broken, and worse, this won't + always be noticeable when using the drive from within MS-DOS. + If you are experiencing weird problems using floppies, this might + be the reason. The only way to correct it is to repair the + floppy drive.

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CD-ROM's

A CD-ROM drive uses an optically read, plastic coated disk. + The information is recorded on the surface of the + disk + + [1] + + in small `holes' aligned along a spiral from the center to the + edge. The drive directs a laser beam along the spiral to read + the disk. When the laser hits a hole, the laser is reflected in + one way; when it hits smooth surface, it is reflected in another + way. This makes it easy to code bits, and therefore information. + The rest is easy, mere mechanics.

CD-ROM drives are slow compared to hard disks. Whereas a + typical hard disk will have an average seek time less than + 15 milliseconds, a fast CD-ROM drive can use tenths of a second + for seeks. The actual data transfer rate is fairly high at + hundreds of kilobytes per second. The slowness means that + CD-ROM drives are not as pleasant to use instead of hard disks + (some Linux distributions provide `live' filesystems on CD-ROM's, + making it unnecessary to copy the files to the hard disk, making + installation easier and saving a lot of hard disk space), although + it is still possible. For installing new software, CD-ROM's are + very good, since it maximum speed is not essential during + installation.

There are several ways to arrange data on a CD-ROM. The most + popular one is specified by the international standard ISO 9660. + This standard specifies a very minimal filesystem, which is + even more crude than the one MS-DOS uses. On the other hand, + it is so minimal that every operating system should be able to + map it to its native system.

For normal UNIX use, the ISO 9660 filesystem is not usable, so + an extension to the standard has been developed, called + the Rock Ridge extension. Rock Ridge allows longer filenames, + symbolic links, and a lot of other goodies, making a CD-ROM + look more or less like any contemporary UNIX filesystem. + Even better, a Rock Ridge filesystem is still a valid ISO 9660 + filesystem, making it usable by non-UNIX systems as well. + Linux supports both ISO 9660 and the Rock Ridge extensions; + the extensions are recognized and used automatically.

The filesystem is only half the battle, however. Most CD-ROM's + contain data that requires a special program to access, and + most of these programs do not run under Linux (except, possibly, + under dosemu, the Linux MS-DOS emulator).

A CD-ROM drive is accessed via the corresponding device file. + There are several ways to connect a CD-ROM drive to the computer: + via SCSI, via a sound card, or via EIDE. The hardware hacking + needed to do this is outside the scope of this book, but the + type of connection decides the device file. See XXX (device-list) + for enlightment.

Notes

[1]

That is, the surface inside + the disk, on the metal disk inside the plastic + coating.

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Tapes

A tape drive uses a tape, similar + + [1] + + to cassettes used for music. A tape is serial in nature, which + means that in order to get to any given part of it, you first have + to go through all the parts in between. A disk can be accessed + randomly, i.e., you can jump directly to any place on the disk. + The serial access of tapes makes them slow.

On the other hand, tapes are relatively cheap to make, + since they do not need to be fast. They can also easily be made + quite long, and can therefore contain a large amount of data. + This makes tapes very suitable for things like archiving and + backups, which do not require large speeds, but benefit from + low costs and large storage capacities.

Notes

[1]

But completely + different, of course.

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Formatting

Formatting is the process of writing marks on the + magnetic media that are used to mark tracks and sectors. + Before a disk is formatted, its magnetic surface is a complete + mess of magnetic signals. When it is formatted, some order is + brought into the chaos by essentially drawing lines where the + tracks go, and where they are divided into sectors. The + actual details are not quite exactly like this, but that is + irrelevant. What is important is that a disk cannot be used + unless it has been formatted.

The terminology is a bit confusing here: in MS-DOS, the word + formatting is used to cover also the process of creating a + filesystem (which will be discussed below). There, the two + processes are often combined, especially for floppies. When + the distinction needs to be made, the real formatting is + called low-level formatting, while making the filesystem + is called high-level formatting. In UNIX circles, + the two are called formatting and making a filesystem, so + that's what is used in this book as well.

For IDE and some SCSI disks the formatting is actually + done at the factory and doesn't need to be repeated; hence most + people rarely need to worry about it. In fact, formatting a + hard disk can cause it to work less well, for example because + a disk might need to be formatted in some very special way to + allow automatic bad sector replacement to work.

Disks that need to be or can be formatted often require a + special program anyway, because the interface to the formatting + logic inside the drive is different from drive to drive. + The formatting program is often either on the controller BIOS, + or is supplied as an MS-DOS program; neither of these can easily + be used from within Linux.

During formatting one might encounter bad spots on the + disk, called bad blocks or bad + sectors. These are sometimes handled by the drive + itself, but even then, if more of them develop, something needs + to be done to avoid using those parts of the disk. The logic to + do this is built into the filesystem; how to add the information + into the filesystem is described below. Alternatively, one + might create a small partition that covers just the bad part of + the disk; this approach might be a good idea if the bad spot is + very large, since filesystems can sometimes have trouble with + very large bad areas.

Floppies are formatted with fdformat. The floppy device + file to use is given as the parameter. For example, the + following command would format a high density, + 3.5 inch floppy in the first floppy drive: + +

$ fdformat /dev/fd0H1440
+Double-sided, 80 tracks, 18 sec/track. Total capacity 1440 kB.
+Formatting ... done
+Verifying ... done
+$
+ + Note that if you want to use an autodetecting device (e.g., + /dev/fd0), you must set the parameters of the device + with setfdprm first. To achieve the same effect as + above, one would have to do the following: + +
$ setfdprm /dev/fd0 1440/1440
+$ fdformat /dev/fd0
+Double-sided, 80 tracks, 18 sec/track. Total capacity 1440 kB.
+Formatting ... done
+Verifying ... done
+$
+ + It is usually more convenient to choose the correct device file + that matches the type of the floppy. Note that it is unwise to + format floppies to contain more information than what they are + designed for.

fdformat will also validate the floppy, i.e., check it + for bad blocks. It will try a bad block several times (you + can usually hear this, the drive noise changes dramatically). + If the floppy is only marginally bad (due to dirt on the + read/write head, some errors are false signals), fdformat won't + complain, but a real error will abort the validation process. + The kernel will print log messages for each I/O error it + finds; these will go to the console or, if syslog + is being used, to the file /usr/log/messages. fdformat + itself won't tell where the error is (one usually doesn't care, + floppies are cheap enough that a bad one is automatically thrown + away). + +

$ fdformat /dev/fd0H1440
+Double-sided, 80 tracks, 18 sec/track. Total capacity 1440 kB.
+Formatting ... done
+Verifying ... read: Unknown error
+$
+ + The badblocks command can be used to search any disk or + partition for bad blocks (including a floppy). It does not + format the disk, so it can be used to check even existing + filesystems. The example below checks a 3.5 inch + floppy with two bad blocks. + +
$ badblocks /dev/fd0H1440 1440
+718
+719
+$
+ + badblocks outputs the block numbers of the bad + blocks it finds. Most filesystems can avoid such bad blocks. They + maintain a list of known bad blocks, which is initialized when the + filesystem is made, and can be modified later. The initial search + for bad blocks can be done by the mkfs command + (which initializes the filesystem), but later checks should be + done with badblocks and the new blocks should + be added with fsck. We'll describe \cmd{mkfs} + and fsck later.

Many modern disks automatically notice bad blocks, and attempt + to fix them by using a special, reserved good block instead. + This is invisible to the operating system. This feature should + be documented in the disk's manual, if you're curious if it + is happening. Even such disks can fail, if the number of bad + blocks grows too large, although chances are that by then the disk + will be so rotten as to be unusable.

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Important parts of the kernel

The Linux kernel consists of several important parts: process + management, memory management, hardware device drivers, filesystem + drivers, network management, and various other bits and pieces. + Figure 2-1 + shows some of them.

Figure 2-1. Some of the more important parts of the Linux kernel

Probably the most important parts of the kernel (nothing else + works without them) are memory management and + process management. Memory management takes care of assigning + memory areas and swap space areas to processes, parts of the + kernel, and for the buffer cache. Process management creates + processes, and implements multitasking by switching the + active process on the processor.

At the lowest level, the kernel contains a hardware device + driver for each kind of hardware it supports. Since the world is + full of different kinds of hardware, the number of hardware device + drivers is large. There are often many otherwise similar pieces + of hardware that differ in how they are controlled by software. + The similarities make it possible to have general classes of + drivers that support similar operations; each member of the class + has the same interface to the rest of the kernel but differs in + what it needs to do to implement them. For example, all disk + drivers look alike to the rest of the kernel, i.e., they all + have operations like `initialize the drive', `read sector N', + and `write sector N'.

Some software services provided by the kernel itself have + similar properties, and can therefore be abstracted into classes. + For example, the various network protocols have been abstracted + into one programming interface, the BSD socket library. Another + example is the virtual filesystem (VFS) + layer that abstracts the filesystem operations away from their + implementation. Each filesystem type provides an implementation + of each filesystem operation. When some entity tries to use + a filesystem, the request goes via the VFS, which routes the + request to the proper filesystem driver.

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Partitions

A hard disk can be divided into several + partitions. Each partition functions as if + it were a separate hard disk. The idea is that if you have one + hard disk, and want to have, say, two operating systems on it, + you can divide the disk into two partitions. Each operating + system uses its partition as it wishes and doesn't touch the + other one's. This way the two operating systems can co-exist + peacefully on the same hard disk. Without partitions one would + have to buy a hard disk for each operating system.

Floppies are not partitioned. There is no technical reason + against this, but since they're so small, partitions would be + useful only very rarely. CD-ROM's are usually also not + partitioned, since it's easier to use them as one big + disk, and there is seldom a need to have several operating + systems on one.

The MBR, boot sectors and partition table

The information about how a hard disk has been partitioned + is stored in its first sector (that is, the first sector of the + first track on the first disk surface). The first sector is the + master boot record (MBR) of the disk; this + is the sector that the BIOS reads in and starts when the machine + is first booted. The master boot record contains a small program + that reads the partition table, checks which partition is active + (that is, marked bootable), and reads the first sector of that + partition, the partition's boot sector + (the MBR is also a boot sector, but it has a special status and + therefore a special name). This boot sector contains another + small program that reads the first part of the operating system + stored on that partition (assuming it is bootable), and then + starts it.

The partitioning scheme is not built into the hardware, or + even into the BIOS. It is only a convention that many + operating systems follow. Not all operating systems do follow + it, but they are the exceptions. Some operating + systems support partitions, but they occupy one partition on + the hard disk, and use their internal partitioning method + within that partition. The latter type exists peacefully + with other operating systems (including Linux), and does not + require any special measures, but an operating system + that doesn't support partitions cannot co-exist on the same + disk with any other operating system.

As a safety precaution, it is a good idea to write down the + partition table on a piece of paper, so that if it ever corrupts + you don't have to lose all your files. (A bad partition table + can be fixed with fdisk). The relevant information + is given by the fdisk -l command: + +

$ fdisk -l /dev/hda
+
+Disk /dev/hda: 15 heads, 57 sectors, 790 cylinders
+Units = cylinders of 855 * 512 bytes
+
+   Device Boot  Begin   Start     End  Blocks   Id  System
+/dev/hda1           1       1      24   10231+  82  Linux swap
+/dev/hda2          25      25      48   10260   83  Linux native
+/dev/hda3          49      49     408  153900   83  Linux native
+/dev/hda4         409     409     790  163305    5  Extended
+/dev/hda5         409     409     744  143611+  83  Linux native
+/dev/hda6         745     745     790   19636+  83  Linux native
+$

Extended and logical partitions

The original partitioning scheme for PC hard disks allowed + only four partitions. This quickly turned out to be too little + in real life, partly because some people want more than four + operating systems (Linux, MS-DOS, OS/2, Minix, FreeBSD, NetBSD, or + Windows/NT, to name a few), but primarily because sometimes it + is a good idea to have several partitions for one + operating system. For example, swap space is usually best put + in its own partition for Linux instead of in the main + Linux partition for reasons of speed (see below).

To overcome this design problem, extended partitions were + invented. This trick allows partitioning a primary + partition into sub-partitions. The + primary partition thus subdivided is the extended partition; the + subpartitions are logical partitions. They behave + like primary + + [1] + + partitions, but are created differently. There is no speed + difference between them.

The partition structure of a hard disk might look like that + in Figure 4-2. The disk is divided into + three primary partitions, the second of which is divided into + two logical partitions. Part of the disk is not partitioned + at all. The disk as a whole and each primary partition has a + boot sector.

Figure 4-2. A sample hard disk partitioning.

Partition types

The partition tables (the one in the MBR, and the ones for + extended partitions) contain one byte per partition that + identifies the type of that partition. This attempts to + identify the operating system that uses the partition, or what + it uses it for. The purpose is to make it possible to avoid + having two operating systems accidentally using the same + partition. However, in reality, operating systems do not + really care about the partition type byte; e.g., Linux + doesn't care at all what it is. Worse, some of them use it + incorrectly; e.g., at least some versions of DR-DOS ignore the + most significant bit of the byte, while others don't.

There is no standardization agency to specify what each byte + value means, but some commonly accepted ones are included in + in Table 4-1. The same list is + available in the Linux fdisk program.

Table 4-1. Partition types (from the Linux fdisk program).

0Empty40Venix 8028694Amoeba BBT
1DOS 12-bit FAT51Novell?a5BSD/386
2XENIX root52Microportb7BSDI fs
3XENIX usr63GNU HURDb8BSDI swap
4DOS 16-bitf <32M64Novellc7Syrinx
5Extended75PC/IXdbCP/M
6DOS 16-bit >=32M80Old MINIXe1DOS access
7OS/2 HPFS81Linux/MINIXe3DOS R/O
8AIX82Linux swapf2DOS secondary
9AIX bootable83Linux nativeffBBT
aOS/2 Boot Manag93Amoeba  

Partitioning a hard disk

There are many programs for creating and removing + partitions. Most operating systems have their own, and it + can be a good idea to use each operating system's own, just + in case it does something unusual that the others can't. + Many of the programs are called fdisk, + including the Linux one, or variations thereof. Details on + using the Linux fdisk are given on its + man page. The cfdisk command is similar + to fdisk, but has a nicer (full screen) + user interface.

When using IDE disks, the boot partition (the partition + with the bootable kernel image files) must be completely + within the first 1024 cylinders. This is because the disk is + used via the BIOS during boot (before the system goes into + protected mode), and BIOS can't handle more than 1024 cylinders. + It is sometimes possible to use a boot partition that is only + partly within the first 1024 cylinders. This works as long + as all the files that are read with the BIOS are within the + first 1024 cylinders. Since this is difficult to arrange, + it is a very bad idea to do it; you never know when + a kernel update or disk defragmentation will result in an + unbootable system. Therefore, make sure your boot partition + is completely within the first 1024 cylinders.

Some newer versions of the BIOS and IDE disks can, in fact, + handle disks with more than 1024 cylinders. If you have such + a system, you can forget about the problem; if you aren't quite + sure of it, put it within the first 1024 cylinders.

Each partition should have an even number of sectors, + since the Linux filesystems use a 1 kilobyte block size, i.e., + two sectors. An odd number of sectors will result in the + last sector being unused. This won't result in any problems, + but it is ugly, and some versions of fdisk + will warn about it.

Changing a partition's size usually requires first backing up + everything you want to save from that partition (preferably the + whole disk, just in case), deleting the partition, creating + new partition, then restoring everything to the new partition. + If the partition is growing, you may need to adjust the sizes + (and backup and restore) of the adjoining partitions as well.

Since changing partition sizes is painful, it is preferable to + get the partitions right + the first time, or have an effective and easy to use backup + system. If you're installing from a media that does not require + much human intervention (say, from CD-ROM, as opposed to floppies), + it is often easy to play with different configuration at first. + Since you don't already have data to back up, it is not so + painful to modify partition sizes several times.

There is a program for MS-DOS, called + fips, which resizes an MS-DOS partition without + requiring the backup and restore, but for other filesystems it + is still necessary.

Device files and partitions

Each partition and extended partition has its own + device file. The naming convention for these files is that a + partition's number is appended after the name of the whole disk, + with the convention that 1-4 are primary partitions (regardless + of how many primary partitions there are) and 5-8 are logical + partitions (regardless of within which primary partition + they reside). For example, /dev/hda1 + is the first primary partition on the first IDE hard disk, and + /dev/sdb7 is the third extended partition on + the second SCSI hard disk. The device list in XXX (device list) + gives more information.

Notes

[1]

Illogical?

PrevHomeNext
FormattingUpFilesystems
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The Linux System Administrators' Guide
PrevChapter 2. Overview of a Linux SystemNext

Major services in a UNIX system

This section describes some of the more important UNIX + services, but without much detail. They are described more + thoroughly in later chapters.

init

The single most important service in a UNIX system is + provided by init. init + is started as the first process of every UNIX system, as the last + thing the kernel does when it boots. When init + starts, it continues the boot process by doing various startup + chores (checking and mounting filesystems, starting daemons, + etc).

The exact list of things that init + does depends on which flavor it is; there are several to choose + from. init usually provides the concept of + single user mode, in which no one can + log in and root uses a shell at the console; the usual mode is + called multiuser mode. Some flavors + generalize this as run levels; single + and multiuser modes are considered to be two run levels, and + there can be additional ones as well, for example, to run X on + the console.

In normal operation, init makes sure + getty is working (to allow users to log in), + and to adopt orphan processes (processes whose parent has died; in + UNIX all processes must + be in a single tree, so orphans must be adopted).

When the system is shut down, it is init + that is in charge of killing all other processes, unmounting all + filesystems and stopping the processor, along with anything else + it has been configured to do.

Logins from terminals

Logins from terminals (via serial lines) and the console + (when not running X) are provided by the getty + program. init starts a separate instance + of getty for each terminal for which + logins are to be allowed. getty reads + the username and runs the login program, + which reads the password. If the username and password + are correct, login runs the shell. + When the shell terminates, i.e., the user logs out, or when + login terminated because the username + and password didn't match, init notices + this and starts a new instance of getty. + The kernel has no notion of logins, this is all handled by the + system programs.

Syslog

The kernel and many system programs produce error, warning, and + other messages. It is often important that these messages can + be viewed later, even much later, so they should be written to + a file. The program doing this is syslog. It can be + configured to sort the messages to different files according to + writer or degree of importance. For example, kernel messages + are often directed to a separate file from the others, since + kernel messages are often more important and need to be read + regularly to spot problems.

Periodic command execution: cron and +at

Both users and system administrators often need + to run commands periodically. For example, the system + administrator might want to run a command to clean the + directories with temporary files (/tmp + and /var/tmp) from old files, to keep the + disks from filling up, since not all programs clean up after + themselves correctly.

The cron service is set up to do this. + Each user has a crontab file, where he + lists the commands he wants to execute and the times they should + be executed. The cron daemon takes care of + starting the commands when specified.

The at service is similar to + cron, but it is once only: the command is + executed at the given time, but it is not repeated.

Graphical user interface

UNIX and Linux don't incorporate the user interface + into the kernel; instead, they let it be implemented by user + level programs. This applies for both text mode and graphical + environments.

This arrangement makes the system more flexible, but has + the disadvantage that it is simple to implement a different + user interface for each program, making the system harder to + learn.

The graphical environment primarily used with Linux + is called the X Window System (X for short). X also does + not implement a user interface; it only implements a window + system, i.e., tools with which a graphical user interface can + be implemented. The three most popular user interface styles + implemented over X are Athena, Motif, and Open Look.

Networking

Networking is the act of connecting two or more computers + so that they can communicate with each other. The actual methods + of connecting and communicating are slightly complicated, but + the end result is very useful.

UNIX operating systems have many networking features. + Most basic services (filesystems, printing, backups, etc) can + be done over the network. This can make system administration + easier, since it allows centralized administration, while + still reaping in the benefits of microcomputing and distributed + computing, such as lower costs and better fault tolerance.

However, this book merely glances at networking; see the + Linux Network Administrators' Guide for + more information, including a basic description of how networks + operate.

Network logins

Network logins work a little differently than normal logins. + There is a separate physical serial line for each terminal via + which it is possible to log in. For each person logging in via + the network, there is a separate virtual network connection, + and there can be any number of these. + + [1] + + It is therefore not possible to run a separate + getty for each possible virtual connection. + There are also several different ways to log in via a network, + telnet and rlogin being + the major ones in TCP/IP networks.

Network logins have, instead of a herd of + gettys, a single daemon per way of logging in + (telnet and rlogin have + separate daemons) that listens for all incoming login attempts. + When it notices one, it starts a new instance of itself to + handle that single attempt; the original instance continues to + listen for other attempts. The new instance works similarly + to getty.

Network file systems

One of the more useful things that can be done with + networking services is sharing files via a network + file system. The one usually used is called the + Network File System, or NFS, developed by Sun.

With a network file system any file operations done by + a program on one machine are sent over the network to another + computer. This fools the program to think that all the files + on the other computer are actually on the computer the program + is running on. This makes information sharing extremely simple, + since it requires no modifications to programs.

Mail

Electronic mail is usually the most important method for + communicating via computer. An electronic letter is stored in a + file using a special format, and special mail programs are used + to send and read the letters.

Each user has an incoming mailbox + (a file in the special format), where all new mail is stored. + When someone sends mail, the mail program locates the receiver's + mailbox and appends the letter to the mailbox file. If the + receiver's mailbox is in another machine, the letter is sent to + the other machine, which delivers it to the mailbox as it best + sees fit.

The mail system consists of many programs. The + delivery of mail to local or remote mailboxes is done by one + program (the mail transfer agent or + MTA, e.g., sendmail + or smail), while the programs users use + are many and varied (mail user agent + or MUA, e.g., pine + or elm). The mailboxes are usually stored + in /var/spool/mail.

Printing

Only one person can use a printer at one time, but it is + uneconomical not to share printers between users. The printer is + therefore managed by software that implements a print + queue: all print jobs are put into a queue and + whenever the printer is done with one job, the next one is sent + to it automatically. This relieves the users from organizing + the print queue and fighting over control of the printer. + + [2] + +

The print queue software also spools + the printouts on disk, i.e., the text is kept in a file while + the job is in the queue. This allows an application program + to spit out the print jobs quickly to the print queue software; + the application does not have to wait until the job is actually + printed to continue. This is really convenient, since it + allows one to print out one version, and not have to wait for + it to be printed before one can make a completely revised new + version.

The filesystem layout

The filesystem is divided into many parts; + usually along the lines of a root filesystem with + /bin, /lib, + /etc, /dev, and + a few others; a /usr filesystem with + programs and unchanging data; a /var + filesystem with changing data (such as log files); and a + /home filesystem for everyone's personal + files. Depending on the hardware configuration and the decisions + of the system administrator, the division can be different; + it can even be all in one filesystem.

Chapter 3 describes the filesystem + layout in some detail; the Linux Filesystem Standard covers it + in somewhat more detail.

Notes

[1]

Well, at least there can be many. Network + bandwidth still being a scarce resource, there is still + some practical upper limit to the number of concurrent + logins via one network connection.

[2]

Instead, they form a new queue + at the printer, waiting for their + printouts, since no one ever seems to be able to get the + queue software to know exactly when anyone's printout is + really finished. This is a great boost to intra-office + social relations.

PrevHomeNext
Important parts of the kernelUpOverview of the Directory Tree
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+ Next: Floppies +Up: Using Disks and Other + Previous: Two kinds of devices +

+

Hard disks

+

+ This subsection introduces terminology related to hard disks. + If you already know the terms and concepts, you can skip this + subsection. +

+ See figure 4.1 for a schematic picture of the + important parts in a hard disk. A hard disk consists of one or + more circular platters,gif of which either or both surfaces are coated with a + magnetic substance used for recording the data. For each + surface, there is a read-write head that examines or + alters the recorded data. The platters rotate on a common axis; + a typical rotation speed is 3600 rotations per minute, + although high-performance hard disks have higher speeds. The + heads move along the radius of the platters; this movement + combined with the rotation of the platters allows the head to + access all parts of the surfaces. +

+ The processor (CPU) and the actual disk communicate through + a disk controller. This relieves the rest of the computer + from knowing how to use the drive, since the controllers for + different types of disks can be made to use the same interface towards + the rest of the computer. Therefore, the computer can say just + ``hey disk, gimme what I want'', instead of a long and complex + series of electric signals to move the head to the proper location + and waiting for the correct position to come under the head + and doing all the + other unpleasant stuff necessary. (In reality, the interface + to the controller is still complex, but much less so than it would + otherwise be.) The controller can also do some other stuff, + such as caching, or automatic bad sector replacement. +

+ The above is usually all one needs to understand about the + hardware. There is also a bunch of other stuff, such as the + motor that rotates the platters and moves the heads, and the + electronics that control the operation of the mechanical + parts, but that is mostly not relevant for understanding the + working principle of a hard disk. +

+ The surfaces are usually divided into concentric rings, called + tracks, and these in turn are divided into sectors. + This division is used to specify locations + on the hard disk and to allocate disk space to files. To find + a given place on the hard disk, one might say ``surface 3, + track 5, sector 7''. Usually the number of sectors is the + same for all tracks, but some hard disks put more sectors in + outer tracks (all sectors are of the same physical size, so + more of them fit in the longer outer tracks). Typically, a + sector will hold 512 bytes of data. The disk itself can't + handle smaller amounts of data than one sector. +

+

  figure1034
+Figure 4.1: A schematic picture of a hard disk.
+

+

+ Each surface is divided into tracks (and sectors) in the same + way. This means that when the head for one surface is on a + track, the heads for the other surfaces are also on the + corresponding tracks. All the corresponding tracks taken + together are called a cylinder. It takes time to move + the heads from one track (cylinder) to another, so by placing + the data that is often accessed together (say, a file) so that + it is within one cylinder, it is not necessary to move the + heads to read all of it. This improves performance. It is + not always possible to place files like this; files that are + stored in several places on the disk are called fragmented. +

+ The number of surfaces (or heads, which is the same thing), + cylinders, and sectors vary a lot; the specification of the + number of each is called the geometry of a hard disk. The + geometry is usually stored in a special, battery-powered memory + location called the CMOS RAM, from where the operating + system can fetch it during bootup or driver initialization. +

+ Unfortunately, the BIOSgif has a design limitation, which makes it + impossible to specify a track number that is larger than 1024 in + the CMOS RAM, + which is too little for a large hard disk. To overcome this, + the hard disk controller lies about the geometry, and + translates the addresses given by the computer into something + that fits reality. For example, a hard disk might have 8 heads, + 2048 tracks, and 35 sectors per trackgif. Its controller could lie to the + computer and claim that it has 16 heads, 1024 tracks, and 35 + sectors per track, thus not exceeding the limit on tracks, and + translates the address that the computer gives it by halving the + head number, and doubling the track number. The math can be + more complicated in reality, because the numbers are not as nice + as here (but again, the details are not relevant for + understanding the principle). This translation distorts the + operating system's view of how the disk is organized, thus making it + impractical to use the all-data-on-one-cylinder trick to boost + performance. +

+ The translation is only a problem for IDE disks. SCSI disks + use a sequential sector number (i.e., the controller translates + a sequential sector number to a head, cylinder, and sector + triplet), and a completely different method for the CPU to talk + with the controller, so they are insulated from the problem. + Note, however, that the computer might not know the real geometry + of an SCSI disk either. +

+ Since Linux often will not know the real geometry of a disk, + its filesystems don't even try to keep files within a single cylinder. + Instead, it tries to assign sequentially numbered sectors to + files, which almost always gives similar performance. The issue + is further complicated by on-controller caches, and automatic + prefetches done by the controller. +

+ Each hard disk is represented by a separate device file. + There can (usually) be only two or four IDE hard disks. + These are known as /dev/hda , /dev/hdb , + /dev/hdc , and /dev/hdd , respectively. SCSI + hard disks are known as /dev/sda , /dev/sdb , and + so on. Similar naming conventions exist for other hard + disk types; see [Anv] for more information. + Note that the device files for the hard disks give access + to the entire disk, with no regard to partitions (which + will be discussed below), and it's easy to mess up the + partitions or the data in them if you aren't careful. + The disks' device files are usually used only to get + access to the master boot record (which will also be + discussed below). +

+

next up previous contents index
+ Next: Floppies +Up: Using Disks and Other + Previous: Two kinds of devices +

+Lars Wirzenius
+Sat Nov 15 02:32:11 EET 1997 +
+ + diff --git a/sag-0.6.1-www/sag-0.6/previous_group_motif.gif b/sag-0.6.1-www/sag-0.6/previous_group_motif.gif new file mode 100644 index 0000000..03ea0dc Binary files /dev/null and b/sag-0.6.1-www/sag-0.6/previous_group_motif.gif differ diff --git a/sag-0.6.1-www/sag-0.6/previous_motif.gif b/sag-0.6.1-www/sag-0.6/previous_motif.gif new file mode 100644 index 0000000..aef90f1 Binary files /dev/null and b/sag-0.6.1-www/sag-0.6/previous_motif.gif differ diff --git a/sag-0.6.1-www/sag-0.6/sag.css b/sag-0.6.1-www/sag-0.6/sag.css new file mode 100644 index 0000000..3970428 --- /dev/null +++ b/sag-0.6.1-www/sag-0.6/sag.css @@ -0,0 +1,10 @@ + +SMALL.TINY { font-size : xx-small } +SMALL.SCRIPTSIZE { font-size : xx-small } +SMALL.FOOTNOTESIZE { font-size : x-small } +SMALL.SMALL { font-size : small } +BIG.LARGE { font-size : large } +BIG.XLARGE { font-size : x-large } +BIG.XXLARGE { font-size : xx-large } +BIG.HUGE { font-size : xx-large } +BIG.XHUGE { font-size : xx-large } diff --git a/sag-0.6.1-www/sag-0.6/up_motif.gif b/sag-0.6.1-www/sag-0.6/up_motif.gif new file mode 100644 index 0000000..3d1aebf Binary files /dev/null and b/sag-0.6.1-www/sag-0.6/up_motif.gif differ diff --git a/sag-0.6.1-www/sysadmin-guide-0.6.1-ANNOUNCE b/sag-0.6.1-www/sysadmin-guide-0.6.1-ANNOUNCE new file mode 100644 index 0000000..1440afa --- /dev/null +++ b/sag-0.6.1-www/sysadmin-guide-0.6.1-ANNOUNCE @@ -0,0 +1,74 @@ +Lars Wirzenius + loudly resents + + a Linux Documentation Project + production + + of the least selling book + by the same name + + the Linux System Administrators' Guide 0.6.1 + just when you thought your system was safe + + starring Super User as Mr. Root + + introducing Lasu as Luser + + special effects by Don Knuth and Leslie Lamport + + music by Crash and Burn + + coming soon to an http://www.iki.fi/liw/linux/sag/ near you + + + +Yes, it's that time of the year again, when Lasu thinks he's an +author! The new version features a conversion to DocBook (instead of +LaTeX), with lots of exciting formatting and spelling bugs for readers +to report, and Debian binary packages! Get your copy today, while the +supplies last! Two for the price of one! No system crash is complete +without the SAG! + + + -x-X-x- + +Table of contents: + + * Introduction + * Overview of a Linux System + * Overview of the Directory Tree + * Using Disks and Other Storage Media + * Allocating disk space + * Memory Management + * Boots And Shutdowns + * init + * Logging In And Out + * Managing user accounts + * Backups + * Keeping Time + * Measuring Holes + * Glossary (DRAFT) + * References + * Index + +The files are: + + sysadmin-guide-0.6.1.tar.gz source code + sysadmin-guide-0.6.1-html.tar.gz HTML + sysadmin-guide-0.6.1.ps.gz Postscript + +Most people will probably only need to download the PS version. +It is all you need if you have a PS printer. (Beware, though: I haven't +tried printing this. Waste of dead trees to test anything.) + +No text or DVI version is available, I do not have the time to produce +one. Don't ask me to. (I'll make one for 1.0.) + +The SAG home page is still at . +All the files are there, soon even an unpacked, browsable version of +the HTML version. + +As usual, feedback is more than welcome. + +I plan to to call the next version 1.0. It'll follow the grand tradition +of version 1.0 being _almost_ useful, but still crashing your system. :) diff --git a/sag-0.6.1-www/sysadmin-guide-0.6.1-html.tar.gz b/sag-0.6.1-www/sysadmin-guide-0.6.1-html.tar.gz new file mode 100644 index 0000000..ddcd298 Binary files /dev/null and b/sag-0.6.1-www/sysadmin-guide-0.6.1-html.tar.gz differ diff --git a/sag-0.6.1-www/sysadmin-guide-0.6.1.ps.gz b/sag-0.6.1-www/sysadmin-guide-0.6.1.ps.gz new file mode 100644 index 0000000..8921e1f Binary files /dev/null and b/sag-0.6.1-www/sysadmin-guide-0.6.1.ps.gz differ diff --git a/sag-0.6.1-www/sysadmin-guide_0.6.1.dsc b/sag-0.6.1-www/sysadmin-guide_0.6.1.dsc new file mode 100644 index 0000000..8225a58 --- /dev/null +++ b/sag-0.6.1-www/sysadmin-guide_0.6.1.dsc @@ -0,0 +1,21 @@ +-----BEGIN PGP SIGNED MESSAGE----- + +Source: sysadmin-guide +Version: 0.6.1 +Binary: sysadmin-guide +Maintainer: Lars Wirzenius +Architecture: all +Standards-Version: 2.4.1.2 +Files: + 261dd83b2f1363294935e43cd54d0916 87773 sysadmin-guide_0.6.1.tar.gz + +-----BEGIN PGP SIGNATURE----- +Version: 2.6.3ia +Charset: noconv + +iQCVAwUBNr8ogIQRll5MupLRAQGwXQQA2KaI12zuVhah70Tflft4gZZsZCNsb4UU +T8jo2iOxyqZ0vQ1KVLGAT9zutJlWngCZHYBCOaDlx87Cm9hvkQtQLfA2N+Kz/+9c +VTlxWaUpUKO7sKK1XbG4mrMb18xUjY+342v1emNIKF3w0DtB4lzfSj5WBOMrxhvY +sDTYXWSMSIc= +=cLmw +-----END PGP SIGNATURE----- diff --git a/sag-0.6.1-www/sysadmin-guide_0.6.1.tar.gz b/sag-0.6.1-www/sysadmin-guide_0.6.1.tar.gz new file mode 100644 index 0000000..80129bd Binary files /dev/null and b/sag-0.6.1-www/sysadmin-guide_0.6.1.tar.gz differ diff --git a/sag-0.6.1-www/sysadmin-guide_0.6.1_all.deb b/sag-0.6.1-www/sysadmin-guide_0.6.1_all.deb new file mode 100644 index 0000000..ad91f7e Binary files /dev/null and b/sag-0.6.1-www/sysadmin-guide_0.6.1_all.deb differ diff --git a/sag-0.6.1-www/sysadmin-guide_0.6.1_i386.changes b/sag-0.6.1-www/sysadmin-guide_0.6.1_i386.changes new file mode 100644 index 0000000..0cf39e5 --- /dev/null +++ b/sag-0.6.1-www/sysadmin-guide_0.6.1_i386.changes @@ -0,0 +1,32 @@ +-----BEGIN PGP SIGNED MESSAGE----- + +Format: 1.5 +Date: Mon, 8 Feb 1999 19:36:57 +0200 +Source: sysadmin-guide +Binary: sysadmin-guide +Architecture: source all +Version: 0.6.1 +Distribution: unstable +Urgency: low +Maintainer: Lars Wirzenius +Description: + sysadmin-guide - The Linux System Administrators' Guide +Changes: + sysadmin-guide (0.6.1) unstable; urgency=low + . + * First Debian release. +Files: + 9e26dc8ab478401cb16018e66899aba0 565 editor optional sysadmin-guide_0.6.1.dsc + 261dd83b2f1363294935e43cd54d0916 87773 editor optional sysadmin-guide_0.6.1.tar.gz + 3a821aa07d4950ec8051cb51d51f6cf3 124420 editor optional sysadmin-guide_0.6.1_all.deb + +-----BEGIN PGP SIGNATURE----- +Version: 2.6.3ia +Charset: noconv + +iQCVAwUBNr8ohYQRll5MupLRAQEurgP/Uue9hU2rpE87Gvb0+hlILXgI5AcgtccT +Lk15t2pS7tgvc1omCQ22midvnYMyRf+svNILDFx0PkffPj9l5epqZDi72FxUJhGK +lG9fUQsgGAn4lZqs3d+xTF5k/YR7LRsjMl7Iy9DDEDOtbkDTdntDJtRU7CJcQiTv ++DK+OiifMp4= +=0Kv8 +-----END PGP SIGNATURE----- diff --git a/sag-0.6.1-www/sysadmin-guide_0.6.1_i386.upload b/sag-0.6.1-www/sysadmin-guide_0.6.1_i386.upload new file mode 100644 index 0000000..bb96602 --- /dev/null +++ b/sag-0.6.1-www/sysadmin-guide_0.6.1_i386.upload @@ -0,0 +1,5 @@ +u sysadmin-guide_0.6.1.tar.gz chiark Mon Feb 8 20:13:03 1999 +u sysadmin-guide_0.6.1.dsc chiark Mon Feb 8 20:13:06 1999 +u sysadmin-guide_0.6.1_all.deb chiark Mon Feb 8 20:13:23 1999 +u sysadmin-guide_0.6.1_i386.changes chiark Mon Feb 8 20:13:27 1999 +a sysadmin-guide_0.6.1_i386.changes debian-devel-changes@lists.debian.org Mon Feb 8 20:13:27 1999 diff --git a/sag-new2.tar.gz b/sag-new2.tar.gz new file mode 100644 index 0000000..a4612d5 Binary files /dev/null and b/sag-new2.tar.gz differ -- cgit v1.2.1