A typical Linux system has, among others, the following directories:
This is the root directory. This is where the whole tree starts.
This directory contains executable programs which are needed in single user mode and to bring the system up or repair it.
Contains static files for the boot loader. This directory only holds the files which are needed during the boot process.
Special or device files, which refer to physical devices.
Contains configuration files which are local to the machine. Some larger software packages, like X11, can have their own subdirectories below /etc. Site-wide configuration files may be placed here or in /usr/etc. Nevertheless, programs should always look for these files in /etc and you may have links for these files to /usr/etc.
When a new user account is created, files from this directory are usually copied into the user's home directory.
Configuration files for the X11 window system.
On machines with home directories for users, these are usually beneath this directory, directly or not. The structure of this directory depends on local administration decisions.
This directory should hold those shared libraries that are necessary to boot the system and to run the commands in the root filesystem.
is a mount point for temporarily mounted filesystems
This is a mount point for the proc filesystem, which provides information about running processes and the kernel.
Like /bin, this directory holds commands needed to boot the system, but which are usually not executed by normal users.
This directory contains temporary files which may be deleted with no notice, such as by a regular job or at system boot up.
This directory is usually mounted from a separate partition. It should hold only sharable, read-only data, so that it can be mounted by various machines running Linux.
The X-Window system.
This is the primary directory for executable pro grams. Most programs executed by normal users which are not needed for booting or for repairing the system and which are not installed locally should be placed in this directory.
is the traditional place to look for X11 executable's; on Linux, it usually is a symbolic link to /usr/X11R6/bin.
This directory holds files containing word lists for spell checkers.
You may find documentation about the installed software packages in this directory.
Site-wide configuration files to be shared between several machines may be stored in this directory. However, commands should always reference those files using the /etc directory. Links from files in /etc should point to the appropriate files in /usr/etc.
Include files for the C compiler.
Include files for the C compiler and the X-Windows system. This is usually a symbolic link to /usr/X11R6/include/X11.
Include files which declare some assembler functions. This used to be a symbolic link to /usr/src/linux/include/asm.
This contains information which may change from system release to system release and used to be a symbolic link to /usr/src/linux/include/linux to get at operating system specific information.
(Note that one should have include files there that work correctly with the current libc and in user space. However, Linux kernel source is not designed to be used with user programs and does not know anything about the libc you are using. It is very likely that things will break if you let /usr/include/asm and /usr/include/linux point at a random kernel tree. Debian systems don't do this and use headers from a known good kernel version, provided in the libc*-dev package.)
Include files to use with the GNU C++ compiler.
Object libraries, including dynamic libraries, plus some executable's which usually are not invoked directly. More complicated programs may have whole subdirectories there.
The usual place for data files associated with X programs, and configuration files for the X system itself. On Linux, it usually is a symbolic link to /usr/X11R6/lib/X11
contains executable's and include files for the GNU C compiler.
Files for the GNU groff document formatting system.
This is where programs which are local to the site typically go.
Binaries for programs local to the site go there.
Configuration files associated with locally installed programs go there.
Files associated with locally installed programs go there.
Info pages associated with locally installed pro grams go there.
Manpages associated with locally installed programs go there.
Locally installed programs for system administration.
Source code for locally installed software.
Manpages traditionally go in there, into their sub directories.
This directory contains program binaries for system administration which are not essential for the boot process, for mounting /usr, or for system repair.
This directory contains subdirectories with specific application data, that can be shared among different architectures of the same OS. Often one finds stuff here that used to live in /usr/doc or /usr/lib or /usr/man.
Manpages go in there, into their subdirectories.
Source files for different parts of the system, included with some packages for reference purposes. Don't work here with your own projects, as files below /usr should be read-only except when installing software
This has always been the traditional place where kernel sources were unpacked. This was important on systems that /usr/include/linux was a symlink here. You should probably use another directory for building the kernel now.
Obsolete. This should be a link to /var/tmp. This link is present only for compatibility reasons and shouldn't be used.
This directory contains files which may change in size, such as spool and log files.
This directory is superseded by /var/log and should be a symbolic link to /var/log.
This directory is used to save backup copies of important system files.
Lock files are placed in this directory. The naming convention for device lock files is LCK..<device> where <device> is the device's name in the filesystem. The format used is that of HDU UUCP lock files, i.e. lock files contain a PID as a 10-byte ASCII decimal number, followed by a newline character.
Miscellaneous log files.
This is where vi saves edit sessions so they can be restored later.
Run-time variable files, like files holding process identifiers (PIDs) and logged user information (utmp). Files in this directory are usually cleared when the system boots.
Spooled (or queued) files for various programs.
Spooled jobs for at(1).
Spooled jobs for cron
Spooled files for printing.
Like /tmp, this directory holds temporary files stored for an unspecified duration.
You can find a more comprehensive description in the hier(7) man page. This layout conforms with the Linux filesystem standard, Release 1.2, and reflects the layout for Debian, RedHat and SuSE Linux.