Rute User's Tutorial and Exposition. 17. Overview of the UNIX Directory Layout
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Here is an overview of how UNIX directories are
structured. This is a simplistic and theoretical overview and not a specification
of the LINUX file system. Chapter 35
contains proper details of permitted directories and the
kinds of files allowed within them.
LINUX systems are divided into hundreds of small packages,
each performing some logical group of operations. On LINUX, many
small, self-contained packages interoperate to give greater
functionality than would large, aggregated pieces of
software. There is also no clear distinction between what is
part of the operating system and what is an application--every
function is just a package.
A software package on a RedHat type system is distributed in a
single RedHat Package Manager (RPM) file that has
a
.rpm extension. On a Debian distribution, the
equivalent is a
.deb package file, and on the
Slackware distribution there are Slackware
.tgz
files.
Each package will unpack as many files, which are placed all over
the system. Packages generally do not create major directories but
unpack files into existing, well-known, major directories.
Note that on a newly installed system there are no
files anywhere that do not belong to some package.
The root directory on a
UNIX system typically looks like this:
5
10
|
drwxr-xr-x 2 root root 2048 Aug 25 14:04 bin
drwxr-xr-x 2 root root 1024 Sep 16 10:36 boot
drwxr-xr-x 7 root root 35840 Aug 26 17:08 dev
drwxr-xr-x 41 root root 4096 Sep 24 20:55 etc
drwxr-xr-x 24 root root 1024 Sep 27 11:01 home
drwxr-xr-x 4 root root 3072 May 19 10:05 lib
drwxr-xr-x 2 root root 12288 Dec 15 1998 lost+found
drwxr-xr-x 7 root root 1024 Jun 7 11:47 mnt
dr-xr-xr-x 80 root root 0 Sep 16 10:36 proc
drwxr-xr-x 3 root root 3072 Sep 23 23:41 sbin
drwxrwxrwt 5 root root 4096 Sep 28 18:12 tmp
drwxr-xr-x 25 root root 1024 May 29 10:23 usr
|
The
/usr directory typically looks like this:
5
10
15
|
drwxr-xr-x 9 root root 1024 May 15 11:49 X11R6
drwxr-xr-x 6 root root 27648 Sep 28 17:18 bin
drwxr-xr-x 2 root root 1024 May 13 16:46 dict
drwxr-xr-x 261 root root 7168 Sep 26 10:55 doc
drwxr-xr-x 7 root root 1024 Sep 3 08:07 etc
drwxr-xr-x 2 root root 2048 May 15 10:02 games
drwxr-xr-x 4 root root 1024 Mar 21 1999 i386-redhat-linux
drwxr-xr-x 36 root root 7168 Sep 12 17:06 include
drwxr-xr-x 2 root root 9216 Sep 7 09:05 info
drwxr-xr-x 79 root root 12288 Sep 28 17:17 lib
drwxr-xr-x 3 root root 1024 May 13 16:21 libexec
drwxr-xr-x 15 root root 1024 May 13 16:35 man
drwxr-xr-x 2 root root 4096 May 15 10:02 sbin
drwxr-xr-x 39 root root 1024 Sep 12 17:07 share
drwxr-xr-x 3 root root 1024 Sep 4 14:38 src
drwxr-xr-x 3 root root 1024 Dec 16 1998 var
|
The
/usr/local directory typically looks like this:
5
10
|
drwxr-xr-x 3 root root 4096 Sep 27 13:16 bin
drwxr-xr-x 2 root root 1024 Feb 6 1996 doc
drwxr-xr-x 4 root root 1024 Sep 3 08:07 etc
drwxr-xr-x 2 root root 1024 Feb 6 1996 games
drwxr-xr-x 5 root root 1024 Aug 21 19:36 include
drwxr-xr-x 2 root root 1024 Sep 7 09:08 info
drwxr-xr-x 9 root root 2048 Aug 21 19:44 lib
drwxr-xr-x 12 root root 1024 Aug 2 1998 man
drwxr-xr-x 2 root root 1024 Feb 6 1996 sbin
drwxr-xr-x 15 root root 1024 Sep 7 09:08 share
|
and the
/usr/X11R6 directory also looks similar. What
is apparent here is that all these directories contain a similar
set of subdirectories. This set of subdirectories is called a
directory superstructure or
superstructure. [To my knowledge this is a new
term not previously used by UNIX administrators.]
The superstructure always contains a
bin and
lib
subdirectory, but almost all others are optional.
Each package will install under one of these superstructures,
meaning that it will unpack many files into various
subdirectories of the superstructure. A RedHat package would
always install under the
/usr or
/
superstructure, unless it is a graphical X Window System
application, which installs under the
/usr/X11R6/
superstructure. Some very large applications may install under a
/opt/<package-name> superstructure, and homemade
packages usually install under the
/usr/local/
superstructure (
local means specific to this very machine).
The directory superstructure under which
a package installs is often called the installation prefix.
Packages almost never install files
across different superstructures. [Exceptions to this are
configuration files which are mostly stored in
/etc/.]
Typically, most of the system is under
/usr. This
directory can be read-only, since packages should never need to
write to this directory--any writing is done under
/var or
/tmp (
/usr/var and
/usr/tmp are often just symlinked to
/var or
/tmp, respectively). The small amount under
/
that is not part of another superstructure (usually about 40
megabytes) performs essential system administration functions.
These are commands needed to bring up or repair the system in
the absence of
/usr.
The list of superstructure subdirectories and their
descriptions is as follows:
-
bin
- Binary executables. Usually all
bin directories are
in the
PATH environment variable so that the shell will search all
these directories for binaries.
-
sbin
- Superuser binary executables. These are programs for system administration only.
Only the
root will have these executables in their
PATH.
-
lib
- Libraries. All other data needed by programs goes in here.
Most packages have their own subdirectory under
lib to
store data files into. Dynamically Linked Libraries
(DLLs or
.so files.) [Executable program code shared by more
than one program in the
bin directory to save disk space and memory.] are stored
directly in
lib.
-
etc
- Et cetera. Configuration files.
-
var
- Variable data. Data files that are continually being re-created or updated.
-
doc
- Documentation. This directory is discussed in Chapter 16.
-
man
- Manual pages. This directory is discussed in Chapter 16.
-
info
- Info pages. This directory is discussed in Chapter 16.
-
share
- Shared data. Architecture-independent files. Files that are independent
of the hardware platform go here. This allows them to be
shared across different machines, even though those machines may have a
different kind of processor altogether.
-
include
- C header files. These are for development.
-
src
- C source files. These are sources to the kernel or locally built packages.
-
tmp
- Temporary files. A convenient place for a running program
to create a file for temporary use.
You can get LINUX to run on a 1.44 megabyte floppy disk if you
trim all unneeded files off an old Slackware distribution with a
2.0.3x kernel. You can compile a small 2.0.3x kernel to about
400 kilobytes (compressed) (see Chapter 42).
A file system can be reduced to 2-3
megabytes of absolute essentials and when compressed will fit
into 1 megabyte. If the total is under 1.44 megabytes, then you
have your LINUX on one floppy.
The file list might be as follows (includes all links):
|
/bin |
/etc |
/lib |
/sbin |
/var |
|
/bin/sh |
/etc/default |
/lib/ld.so |
/sbin/e2fsck |
/var/adm |
|
/bin/cat |
/etc/fstab |
/lib/libc.so.5 |
/sbin/fdisk |
/var/adm/utmp |
|
/bin/chmod |
/etc/group |
/lib/ld-linux.so.1 |
/sbin/fsck |
/var/adm/cron |
|
/bin/chown |
/etc/host.conf |
/lib/libcurses.so.1 |
/sbin/ifconfig |
/var/spool |
|
/bin/cp |
/etc/hosts |
/lib/libc.so.5.3.12 |
/sbin/iflink |
/var/spool/uucp |
|
/bin/pwd |
/etc/inittab |
/lib/libtermcap.so.2.0.8 |
/sbin/ifsetup |
/var/spool/uucp/SYSLOG |
|
/bin/dd |
/etc/issue |
/lib/libtermcap.so.2 |
/sbin/init |
/var/spool/uucp/ERRLOG |
|
/bin/df |
/etc/utmp |
/lib/libext2fs.so.2.3 |
/sbin/mke2fs |
/var/spool/locks |
|
/bin/du |
/etc/networks |
/lib/libcom_err.so.2 |
/sbin/mkfs |
/var/tmp |
|
/bin/free |
/etc/passwd |
/lib/libcom_err.so.2.0 |
/sbin/mkfs.minix |
/var/run |
|
/bin/gunzip |
/etc/profile |
/lib/libext2fs.so.2 |
/sbin/mklost+found |
/var/run/utmp |
|
/bin/gzip |
/etc/protocols |
/lib/libm.so.5.0.5 |
/sbin/mkswap |
|
|
/bin/hostname |
/etc/rc.d |
/lib/libm.so.5 |
/sbin/mount |
/home/user |
|
/bin/login |
/etc/rc.d/rc.0 |
/lib/cpp |
/sbin/route |
|
|
/bin/ls |
/etc/rc.d/rc.K |
|
/sbin/shutdown |
/mnt |
|
/bin/mkdir |
/etc/rc.d/rc.M |
/usr |
/sbin/swapoff |
|
|
/bin/mv |
/etc/rc.d/rc.S |
/usr/adm |
/sbin/swapon |
/proc |
|
/bin/ps |
/etc/rc.d/rc.inet1 |
/usr/bin |
/sbin/telinit |
|
|
/bin/rm |
/etc/rc.d/rc.6 |
/usr/bin/less |
/sbin/umount |
/tmp |
|
/bin/stty |
/etc/rc.d/rc.4 |
/usr/bin/more |
/sbin/agetty |
|
|
/bin/su |
/etc/rc.d/rc.inet2 |
/usr/bin/sleep |
/sbin/update |
/dev/<various-devices> |
|
/bin/sync |
/etc/resolv.conf |
/usr/bin/reset |
/sbin/reboot |
|
|
/bin/zcat |
/etc/services |
/usr/bin/zless |
/sbin/netcfg |
|
|
/bin/dircolors |
/etc/termcap |
/usr/bin/file |
/sbin/killall5 |
|
|
/bin/mount |
/etc/motd |
/usr/bin/fdformat |
/sbin/fsck.minix |
|
|
/bin/umount |
/etc/magic |
/usr/bin/strings |
/sbin/halt |
|
|
/bin/bash |
/etc/DIR_COLORS |
/usr/bin/zgrep |
/sbin/badblocks |
|
|
/bin/domainname |
/etc/HOSTNAME |
/usr/bin/nc |
/sbin/kerneld |
|
|
/bin/head |
/etc/mtools |
/usr/bin/which |
/sbin/fsck.ext2 |
|
|
/bin/kill |
/etc/ld.so.cache |
/usr/bin/grep |
|
|
|
/bin/tar |
/etc/psdevtab |
/usr/sbin |
|
|
|
/bin/cut |
/etc/mtab |
/usr/sbin/showmount |
|
|
|
/bin/uname |
/etc/fastboot |
/usr/sbin/chroot |
|
|
|
/bin/ping |
|
/usr/spool |
|
|
|
/bin/ln |
|
/usr/tmp |
|
|
|
/bin/ash |
|
|
|
|
Note that the
etc directory differs from that of a
RedHat distribution. The system startup files
/etc/rc.d
are greatly simplified under Slackware.
The
/lib/modules directory has been stripped for the
creation of this floppy.
/lib/modules/2.0.36 would
contain dynamically loadable kernel drivers (modules). Instead,
all needed drivers are compiled into the kernel for simplicity
(explained in Chapter 42).
At some point, try creating a single floppy distribution
as an exercise. This task should be most instructive to a
serious system administrator. At the very least, you
should look through all of the commands in the
bin
directories and the
sbin directories above and browse
through the man pages of any that are unfamiliar.
The preceding file system comes from the
morecram-1.3
package available from
http://rute.sourceforge.net/morecram-1.3.tar.gz.
It can be downloaded to provide a useful rescue and setup
disk. Note that there are many such rescue disks
available which are more current than
morecram.
Next: 18. UNIX Devices
Up: rute
Previous: 16. Pre-installed Documentation
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|
