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diff --git a/sag-0.6.1-www/sag-0.6.1.html/c212.html b/sag-0.6.1-www/sag-0.6.1.html/c212.html new file mode 100644 index 0000000..1060903 --- /dev/null +++ b/sag-0.6.1-www/sag-0.6.1.html/c212.html @@ -0,0 +1,432 @@ +<!DOCTYPE HTML PUBLIC "-//Norman Walsh//DTD DocBook HTML 1.0//EN"> +<HTML +><HEAD +><TITLE +>Overview of the Directory Tree</TITLE +><META +NAME="GENERATOR" +CONTENT="Modular DocBook HTML Stylesheet"><LINK +REL="HOME" +TITLE="The Linux System Administrators' Guide" +HREF="book1.html"><LINK +REL="PREVIOUS" +TITLE="Major services in a UNIX system" +HREF="x94.html"><LINK +REL="NEXT" +TITLE="The root filesystem" +HREF="x267.html"></HEAD +><BODY +BGCOLOR="#FFFFFF" +TEXT="#000000" +><DIV +CLASS="NAVHEADER" +><TABLE +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TH +COLSPAN="3" +ALIGN="center" +>The Linux System Administrators' Guide</TH +></TR +><TR +><TD +WIDTH="10%" +ALIGN="left" +VALIGN="bottom" +><A +HREF="x94.html" +>Prev</A +></TD +><TD +WIDTH="80%" +ALIGN="center" +VALIGN="bottom" +></TD +><TD +WIDTH="10%" +ALIGN="right" +VALIGN="bottom" +><A +HREF="x267.html" +>Next</A +></TD +></TR +></TABLE +><HR +ALIGN="LEFT" +WIDTH="100%"></DIV +><DIV +CLASS="CHAPTER" +><H1 +><A +NAME="DIR-TREE-OVERVIEW" +>Chapter 3. Overview of the Directory Tree</A +></H1 +><DIV +CLASS="TOC" +><DL +><DT +><B +>Table of Contents</B +></DT +><DT +><A +HREF="c212.html#AEN218" +>Background</A +></DT +><DT +><A +HREF="x267.html" +>The root filesystem</A +></DT +><DT +><A +HREF="x338.html" +>The <TT +CLASS="FILENAME" +>/etc</TT +> directory</A +></DT +><DT +><A +HREF="x463.html" +>The <TT +CLASS="FILENAME" +>/dev</TT +> directory</A +></DT +><DT +><A +HREF="x472.html" +>The <TT +CLASS="FILENAME" +>/usr</TT +> filesystem</A +></DT +><DT +><A +HREF="x531.html" +>The <TT +CLASS="FILENAME" +>/var</TT +> filesystem</A +></DT +><DT +><A +HREF="x595.html" +>The <TT +CLASS="FILENAME" +>/proc</TT +> filesystem</A +></DT +></DL +></DIV +><BLOCKQUOTE +><P +>“ 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) </P +></BLOCKQUOTE +><P +>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.</P +><DIV +CLASS="SECT1" +><H1 +CLASS="SECT1" +><A +NAME="AEN218" +>Background</A +></H1 +><P +>This chapter is loosely based on the <I +CLASS="CITETITLE" +>Linux + filesystem standard</I +>, 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.</P +><P +>This chapter is not as detailed as the FSSTND. A system + administrator should also read the FSSTND for a complete + understanding.</P +><P +>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.</P +><P +>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, <TT +CLASS="FILENAME" +>/usr</TT +>, <TT +CLASS="FILENAME" +>/var</TT +>, and + <TT +CLASS="FILENAME" +>/home</TT +> filesystems (see + <A +HREF="c212.html#FSTREE" +>Figure 3-1</A +>). 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.</P +><DIV +CLASS="FIGURE" +><P +><B +><A +NAME="FSTREE" +>Figure 3-1. Parts of a Unix directory tree. Dashed lines indicate partition limits.</A +></B +></P +><P +><IMG +SRC="fstree.gif"></P +></DIV +><P +>The roles of the different parts of the directory tree are + described below. + + <P +></P +><UL +><LI +><P +>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.</P +></LI +><LI +><P +> The <TT +CLASS="FILENAME" +>/usr</TT +> filesystem + contains all commands, libraries, manual pages, and + other unchanging files needed during normal operation. + No files in <TT +CLASS="FILENAME" +>/usr</TT +> 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 + <TT +CLASS="FILENAME" +>/usr</TT +>), and can make administration + easier (only the master <TT +CLASS="FILENAME" +>/usr</TT +> 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.</P +></LI +><LI +><P +>The <TT +CLASS="FILENAME" +>/var</TT +> + 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 <TT +CLASS="FILENAME" +>/var</TT +> + has been somewhere below <TT +CLASS="FILENAME" +>/usr</TT +>, but + that made it impossible to mount <TT +CLASS="FILENAME" +>/usr</TT +> + read-only.</P +><P +></P +></LI +><LI +><P +> The <TT +CLASS="FILENAME" +>/home</TT +> + 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 <TT +CLASS="FILENAME" +>/home</TT +> might have to be + broken on several filesystems, which requires adding an + extra naming level below <TT +CLASS="FILENAME" +>/home</TT +>, + e.g., <TT +CLASS="FILENAME" +>/home/students</TT +> and + <TT +CLASS="FILENAME" +>/home/staff</TT +>.</P +></LI +></UL +> </P +><P +>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 <I +CLASS="EMPHASIS" +>names</I +> + work; even if, say, <TT +CLASS="FILENAME" +>/var</TT +> and + <TT +CLASS="FILENAME" +>/usr</TT +> are actually on the same + partition, the names <TT +CLASS="FILENAME" +>/usr/lib/libc.a</TT +> + and <TT +CLASS="FILENAME" +>/var/log/messages</TT +> must work, for + example by moving files below <TT +CLASS="FILENAME" +>/var</TT +> + into <TT +CLASS="FILENAME" +>/usr/var</TT +>, and + making <TT +CLASS="FILENAME" +>/var</TT +> a symlink to + <TT +CLASS="FILENAME" +>/usr/var</TT +>.</P +><P +>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).</P +></DIV +></DIV +><DIV +CLASS="NAVFOOTER" +><HR +ALIGN="LEFT" +WIDTH="100%"><TABLE +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +><A +HREF="x94.html" +>Prev</A +></TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +><A +HREF="book1.html" +>Home</A +></TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +><A +HREF="x267.html" +>Next</A +></TD +></TR +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +>Major services in a UNIX system</TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +> </TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +>The root filesystem</TD +></TR +></TABLE +></DIV +></BODY +></HTML +>
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