All Unix systems have certain standard directories. Although the underlying operating system doesn't care about the precise directory structure, many of the standard Unix utilities have specific directory names hard coded into their source code. Here is a list of some of the more interesting directories and what you might find in them.
There is an effort in progress to standardize the organization of the Unix file system in order to facilitate the creation of portable scripts and administrative tools. For more information see the Filesystem Hierarchy Standard at http://www.pathname.com/fhs/.
Common Unix Directories
/bin
/usr/bin
Here are where all the utility programs are stored. The most commonly used
programs are put into /bin. The less commonly used programs are
put into /usr/bin. On some systems, /bin may
be the only directory of the two available when the system is booted into single user
mode.
/tmp
,
/var/tmp
Many programs write temporary files into /tmp. These
directories are wide open to all users. Files stored in /tmp
should not stay there very long.
/lib
,
/usr/lib
Here is where compiled library files such as the C library are stored. Also
certain programs that are not normally executed directly by the user are stored here.
For example, the C compiler has two passes. They are stored in
/lib. The dictionary for the spell program, the macro packages
for nroff, and many other things are stored in
/usr/lib.
/usr/share/man
Here is where the online manual is stored. This directory contains subdirectories
for each manual section. For example, /usr/share/man/man1
contains all the manual pages for section 1 in compressed form.
/usr/include
Here is where the header files used with C programming are stored. This directory
is the standard place where the C compile looks when it sees header files included
with the <...> notation. Notice that there are several subdirectories under
/usr/include as well.
/usr/local
This directory contains locally produced items. For example,
/usr/local/bin contains programs that are not part of the
normal Unix distribution, but that are of interest to all users at a particular site.
Also under /usr/local are directories for local administrative
commands, local manual pages, and so forth.
/var
The /var directory is where "variable" files are stored.
These files tend to be highly volitale and may change from minute to minute. Incoming
mail, log files, and other such things are often stored here.
/var/adm
On many systems this is where various administrative files are stored. For
example, account files, the shutdown log file, and the file that records information
about telnet connections are stored here. On most Linux systems,
/var/log contains all the log files.
/var/spool
This directory is used for spooling operations of various types. The print daemon, uucp, cron, mail and various other Unix programs that do things automatically use this directory for temporary files and work files.
/home
On some old systems, user home directories are all kept under
/usr. However since there are often many home directories and
since they often need to be managed with a different policy than that used by the rest
of the system, most current systems store user home directories under
/home. Note that in Unix each ordinary user has a personal
directory for storing his/her files. Many Unix applications assume such a directory
exists and expect to store all of a user's personal configuration information there.
Unix does not have a "registry" in the sense of Windows.
/etc
This directory contains files and programs of interest to the system administrator. Many system configuration files are in /etc.
/dev
This directory contains the special device files. Unix treats all I/O devices as
if they were files. By tradition, all such files appear in
/dev.