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Database files for NIS, formerly known as the Sun Yellow Pages (YP).
Like /tmp, this directory holds temporary files stored for an unspecified duration.
Spooled files for uucp(1) (optional).
Spooled files for the smail(1) mail delivery program.
Spooled files for rwhod(8) (optional).
Spool directory for news (optional).
Queued outgoing mail (optional).
Replaced by /var/mail.
Spools for a specific printer (optional).
Spooled files for printing (optional).
Spooled jobs for cron(8).
Spooled jobs for at(1).
Spooled (or queued) files for various programs.
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.
Reserved for historical reasons.
Reserved for historical reasons.
Users' mailboxes. Replaces /var/spool/mail.
Variable data for /opt.
Miscellaneous log files.

lock files contain a PID as a 10-byte ASCII decimal number, followed by a newline character.

Lock files are placed in this directory. The naming convention for device lock files is LCK.. where is the device's name in the filesystem. The format used is that of HDU UUCP lock files, that is,
Variable data for /usr/local.
Packaging support files (optional).
State data for packages and subsystems (optional).
These directories must be used for all distribution packaging support.
Editor backup files and state (optional).
X display manager variable data (optional).
Miscellaneous state data.
State directory for hwclock (optional).
Variable files containing color management information (optional).
Variable state information for programs.
Variable game data (optional).
Reserved for historical reasons.
System crash dumps (optional).
These directories contain preformatted manual pages according to their man page section.(The use of preformatted manual pages is deprecated.)
/var/catman/cat[1-9] or /var/cache/man/cat[1-9]
Package specific cache data (optional).
WWW proxy or cache data (optional).
Locally formatted man pages (optional).
Locally generated fonts (optional).
Data cached for programs.
Reserved for historical reasons.
Process accounting logs (optional).

/var   This directory contains files which may change in size, such as spool and log files.

This link is present only for compatibility reasons and shouldn't be used.

Kernel source

Some distributions put here the source for the default kernel they ship.
You should probably use another directory when building your own kernel.


Source files

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

Files for timezone information (optional).
MathML DTD (optional).
XHTML DTD (optional).
DocBook DTD (optional).
Files for XML (optional).
Troff macros that are not distributed with groff (optional).
The database for terminfo (optional).
MathML DTD (optional).
HTML DTD (optional).
TEI DTD (optional).
DocBook DTD (optional).
Files for SGML (optional).
Postscript Printer Definition (PPD) files (optional).
The message catalogs for native language support go here (optional).
Miscellaneous data that can be shared among different architectures of the same OS.
Manual pages

These directories contain manual pages for the specific locale in source code form. Systems which use a unique language and code set for all manual pages may omit the substring.

Manual pages go here in subdirectories according to the man page sections.
Locale information goes here (optional).
Info pages go here (optional).
Static data files for games in /usr/games (optional).
Documentation about installed programs (optional).
List of English words (optional).
Contains the word lists used by spell checkers (optional).
Contains color management information, like International Color Consortium (ICC) Color profiles (optional).
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
This directory contains program binaries for system administration which are not essential for the boot process, for mounting /usr, or for system repair.
Replaced by /usr/share/man.
Source code for locally installed software.
Local application data that can be shared among different architectures of the same OS.
Locally installed programs for system administration.
Man pages associated with locally installed programs.
Info pages associated with locally installed programs.
Header files for the local C compiler.
These directories are variants of /usr/local/lib on system which support more than one binary format requiring separate libraries (optional).
Files associated with locally installed programs.
Binaries for locally installed games.
Configuration files associated with locally installed programs.
Local documentation.
Binaries for programs local to the site.
This is where programs which are local to the site typically go.
Files for uucp(1).
Files for the GNU groff document formatting system.
contains executables and include files for the GNU C compiler, gcc(1).
Directory contains binaries for internal use only and they are not meant to be executed directly by users shell or scripts.
Object libraries, including dynamic libraries, plus some executables which usually are not invoked directly. More complicated programs may have whole subdirectories there.
Include files to use with the GNU C++ compiler.
nel version, provided in the libc*-dev package.)```
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 ker‐```
(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
#### 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.
BSD compatibility include files (optional).
Include files for the C compiler.
Binaries for games and educational programs (optional).

point to the appropriate files in /usr/etc.


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

Replaced by /usr/share/doc.
Replaced by /usr/share/dict.
Commands for the MH mail handling system (optional).
#### This is the primary directory for executable programs.  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
Data files associated with the X-Window system.
The X-Window system, version 11 release 6 (present in FHS 2.3, removed in FHS 3.0).

This directory is usually mounted from a separate partition.
It should hold only shareable, read-only data, so that it can be mounted by various machines running Linux.


This directory contains temporary files which may be deleted with no notice, such as by a regular job or at system boot up.


This is a mount point for the sysfs filesystem, which provides information about the kernel like /proc, but better structured, following the formalism of kobject infrastructure.


This directory contains site-specific data that is served by this system.


Like /bin, this directory holds commands needed to boot the system, but which are usually not executed by normal users.


This directory contains information which describes the system since it was booted.
Once this purpose was served by /var/run and programs may continue to use it.


This directory is usually the home directory for the root user (optional).


This is a mount point for the proc filesystem, which provides information about running processes and the kernel.
This pseudo-filesystem is described in more detail in proc(5).


This directory should contain add-on packages that contain static files.


This directory is a mount point for a temporarily mounted filesystem.
In some distributions, /mnt contains subdirectories intended to be sed as mount points for several temporary filesystems.

USB drive (optional).
Zip drive (optional).
CD writer (optional).
CD-ROM drive (optional).
Floppy drive (optional).
appending a digit to the name of those available above starting with '0', but the unqualified name must also exist.
/media This directory contains mount points for removable media such as CD and DVD disks or USB sticks. On systems where more than one device exists for mounting a certain type of media, mount directories can be created by
This directory contains items lost in the filesystem. These items are usually chunks of files mangled as a consequence of a faulty disk or a system crash.
Loadable kernel modules (optional).
These directories are variants of /lib on system which support more than one binary format requiring separate libraries (optional).

/lib   This directory should hold those shared libraries that are necessary to boot the system and to run the commands in the root filesystem.

/home  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 (optional).
This directory contains the configuration files for XML (optional).
Configuration files for the X11 window system (optional).
When a new user account is created, files from this directory are usually copied into the user's home directory.
This directory contains the configuration files for SGML (optional).
Host-specific configuration files for add-on applications installed in /opt.

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Last update: December 4, 2022 19:31:07