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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 @@ +<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> +<!--Converted with LaTeX2HTML 96.1-h (September 30, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds --> +<HTML> +<HEAD> +<TITLE>Background</TITLE> +<META NAME="description" CONTENT="Background"> +<META NAME="keywords" CONTENT="sag"> +<META NAME="resource-type" CONTENT="document"> +<META NAME="distribution" CONTENT="global"> +<LINK REL=STYLESHEET HREF="sag.css"> +</HEAD> +<BODY LANG="EN" > + <A NAME="tex2html556" HREF="node22.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html554" HREF="node20.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html548" HREF="node20.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html558" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html559" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html557" HREF="node22.html">The root filesystem</A> +<B>Up:</B> <A NAME="tex2html555" HREF="node20.html">Overview of the Directory </A> +<B> Previous:</B> <A NAME="tex2html549" HREF="node20.html">Overview of the Directory </A> +<BR> <P> +<H1><A NAME="SECTION00410000000000000000">Background</A></H1> +<P> + This chapter is loosely based on the Linux filesystem + standard, FSSTND, version 1.2 (see the bibliography, + [<A HREF="node113.html#fsstnd-1.2">Qui95</A>]), 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> + This chapter is not as detailed as the FSSTND. A system + administrator should also read the FSSTND for a complete + understanding. +<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> + 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>/usr</tt><A NAME="638"> </A>, <tt>/var</tt><A NAME="640"> </A>, and + <tt>/home</tt><A NAME="642"> </A> filesystems (see figure <A HREF="node21.html#figfstree">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> + <P><A NAME="428"> </A><A NAME="figfstree"> </A><IMG WIDTH=438 HEIGHT=220 ALIGN=BOTTOM ALT="figure424" SRC="img3.gif"><BR> +<STRONG>Figure 3.1:</STRONG> Parts of a Unix directory tree. + Dashed lines indicate partition limits.<BR> +<P> +<P> + The roles of the different parts of the directory tree are + described below. + <UL> +<LI> + 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. +<LI> + The <tt>/usr</tt><A NAME="644"> </A> filesystem contains all commands, libraries, manual + pages, and other unchanging files needed during normal operation. + No files in <tt>/usr</tt><A NAME="646"> </A> 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>/usr</tt><A NAME="648"> </A>), and can make administration easier + (only the master <tt>/usr</tt><A NAME="650"> </A> 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. +<LI> + The <tt>/var</tt><A NAME="652"> </A> 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>/var</tt><A NAME="654"> </A> has been somewhere below <tt>/usr</tt><A NAME="656"> </A>, + but that made it impossible to mount <tt>/usr</tt><A NAME="658"> </A> read-only. +<LI> + The <tt>/home</tt><A NAME="660"> </A> 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>/home</tt><A NAME="662"> </A> might have to + be broken on several filesystems, which requires adding an extra + naming level below <tt>/home</tt><A NAME="664"> </A>, e.g., <tt>/home/students</tt><A NAME="666"> </A> and + <tt>/home/staff</tt><A NAME="668"> </A>. + </UL> + 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 <em>names</em> + work; even if, say, <tt>/var</tt><A NAME="670"> </A> and <tt>/usr</tt><A NAME="672"> </A> are actually on the + same partition, the names <tt>/usr/lib/libc.a</tt><A NAME="674"> </A> and + <tt>/var/adm/messages</tt><A NAME="676"> </A> must work, for example by moving files + below <tt>/var</tt><A NAME="678"> </A> into <tt>/usr/var</tt><A NAME="680"> </A>, and making <tt>/var</tt><A NAME="682"> </A> a symlink + to <tt>/usr/var</tt><A NAME="684"> </A>. +<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> +<HR><A NAME="tex2html556" HREF="node22.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html554" HREF="node20.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html548" HREF="node20.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html558" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html559" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html557" HREF="node22.html">The root filesystem</A> +<B>Up:</B> <A NAME="tex2html555" HREF="node20.html">Overview of the Directory </A> +<B> Previous:</B> <A NAME="tex2html549" HREF="node20.html">Overview of the Directory </A> +<P><ADDRESS> +<I>Lars Wirzenius <BR> +Sat Nov 15 02:32:11 EET 1997</I> +</ADDRESS> +</BODY> +</HTML> |