Editing Filesystem Hierarchy Standard (section)

==Directory structure==
[[File:Root directory hierarchy on Linux screenshot.webp|300px|thumb|Filesystem hierarchy in [[openSUSE]]]]
In the FHS, all files and [[directory (file systems)|directories]] appear under the [[root directory]] <code>/</code>, even if they are stored on different physical or virtual devices. Some of these directories only exist in a particular system if certain subsystems, such as the [[X Window System]], are installed.

Most of these directories exist in all [[Unix-like]] operating systems and are generally used in much the same way; however, the descriptions here are those used specifically for the FHS and are not considered authoritative for platforms other than Linux.

{| class="wikitable" summary="A description of the hierarchy specified in the FHS."
|-
!Directory
!Description
|-
|<code>/</code>
|''Primary hierarchy'' root and [[root directory]] of the entire file system hierarchy.
|-
|<code>/bin</code>
|Essential command [[executable|binaries]] that need to be available in [[single-user mode]], including to bring up the system or repair it,<ref>{{Cite web|title=hier(7) - Linux manual page|url=https://man7.org/linux/man-pages/man7/hier.7.html|access-date=2021-01-06|website=man7.org}}</ref> for all users (e.g., [[cat (Unix)|cat]], [[ls]], [[cp (Unix)|cp]]).
|-
|<code>[[Boot folder|/boot]]</code>
|[[Boot loader]] files (e.g., [[Kernel (operating system)|kernel]]s, [[initrd]]).
|-
|<code>[[/dev]]</code>
|[[Device file]]s (e.g., <code>[[Null device|/dev/null]]</code>, <code>/dev/disk0</code>,  <code>/dev/sda1</code>, <code>/dev/tty</code>, <code>[[%2Fdev%2Frandom]]</code>).
|-
|<code>/etc</code>
<!-- Please see the talk page before changing this -->
|Host-specific system-wide [[configuration file]]s.<br />
There has been controversy over the meaning of the name itself. In early versions of the UNIX Implementation Document from Bell Labs, <code>/etc</code> is referred to as the ''[[et cetera|etcetera]] directory'',<ref>{{cite book |author=J. DeFelicc |title=Preliminary Release of UNIX Implementation Document |date=1972-03-17 |id=IMO.1-1 |section=E.0 |page=8 |issue=D |url=http://www.bitsavers.org/pdf/att/unix/Early_UNIX/PreliminaryUnixImplementationDocument_Jun72.pdf |access-date=6 June 2024}}</ref> as this directory historically held everything that did not belong elsewhere (however, the FHS restricts <code>/etc</code> to static configuration files and may not contain binaries).<ref name="/etc">{{cite web |url= http://www.pathname.com/fhs/pub/fhs-2.3.html#ETCHOSTSPECIFICSYSTEMCONFIGURATION |title=/etc : Host-specific system configuration |work=Filesystem Hierarchy Standard 2.3|access-date=18 February 2016}}</ref> Since the publication of early documentation, the directory name has been re-explained in various ways. Recent interpretations include [[backronym]]s such as "Editable Text Configuration" or "Extended Tool Chest".<ref>[http://ask.slashdot.org/article.pl?sid=07/03/03/028258 Define - /etc?], Posted by Cliff, 3 March 2007 - Slashdot.</ref>
|-
|<code>/etc/opt</code>
|Configuration files for add-on packages stored in <code>/opt</code>.
|-
|<code>/etc/sgml</code>
|Configuration files, such as catalogs, for software that processes [[SGML]].
|-
|<code>/etc/X11</code>
|Configuration files for the [[X Window System]], version 11.
|-
|<code>/etc/xml</code>
|Configuration files, such as catalogs, for software that processes [[XML]].
|-
|<code>/home</code>
|Users' [[home directory|home directories]], containing saved files, personal settings, etc.
|-
|<code>/lib</code>
|[[Library (computer science)|Libraries]] essential for the [[binaries]] in <code>/bin</code> and <code>/sbin</code>.
|-
|<code>/lib&lt;qual&gt;</code>
|Alternate format essential libraries. These are typically used on systems that support more than one executable code format, such as systems supporting [[32-bit]] and [[64-bit]] versions of an [[instruction set]].  Such directories are optional, but if they exist, they have some requirements.
|-
|<code>/media</code>
|Mount points for [[removable media]] such as [[CD-ROM]]s (appeared in FHS-2.3 in 2004).
|-
|<code>/mnt</code>
|Temporarily [[mount (computing)|mounted]] filesystems.
|-
|<code>/opt</code>
|Add-on [[application software]] [[Software package (installation)|packages]].<ref name="/opt">{{cite web |url=http://www.pathname.com/fhs/pub/fhs-2.3.html#OPTADDONAPPLICATIONSOFTWAREPACKAGES |title=/opt : Add-on application software packages |work=Filesystem Hierarchy Standard 2.3 |access-date=18 February 2016}}</ref>
|-
|<code>[[/proc]]</code>
|Virtual [[File system|filesystem]] providing [[process (computing)|process]] and [[kernel (operating system)|kernel]] information as files. In Linux, corresponds to a [[procfs]] mount. Generally, automatically generated and populated by the system, on the fly.
|-
|<code>/root</code>
|[[Home directory]] for the [[superuser|root]] user.
|-
|<code>/run</code>
|Run-time variable data: Information about the running system since last boot, e.g., currently logged-in users and running [[Daemon (computer software)|daemons]]. Files under this directory must be either removed or truncated at the beginning of the boot process, but this is not necessary on systems that provide this directory as a [[temporary filesystem]] ([[tmpfs]]) (appeared in FHS-3.0 in 2015). 
|-
|<code>/sbin</code>
|Essential system binaries (e.g., [[fsck]], [[init]], [[route (command)|route]]).
|-
|<code>/srv</code>
|Site-specific data served by this system, such as data and scripts for web servers, data offered by [[FTP]] servers, and repositories for [[version control systems]] (appeared in FHS-2.3 in 2004).
|-
|<code>[[/sys]]</code>
|Contains information about devices, drivers, and some kernel features.<ref name="/sys">{{cite web |url=https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch06.html#sysKernelAndSystemInformation |title=/sys : Kernel and system information virtual filesystem |work=Filesystem Hierarchy Standard 3.0 |access-date=4 June 2017}}</ref>
|-
|<code>/tmp</code>
|[[Temporary folder|Directory for temporary files]] (see also <code>/var/tmp</code>). Often not preserved between system reboots and may be severely size-restricted. 
|-
|<code>/usr</code>
<!-- ##### Please SEE THE TALK PAGE before changing this ##### -->
|''Secondary hierarchy'' for read-only user data; contains the majority of ([[multi-user|multi-]])user utilities and applications.  Should be shareable and read-only.<ref>{{cite web|url=https://refspecs.linuxfoundation.org/FHS_2.3/fhs-2.3.html#THEUSRHIERARCHY|work=Filesystem Hierarchy Standard 2.3|title=Chapter 4. The /usr Hierarchy}}</ref><ref>{{cite web|url=https://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.html#purpose18|work=Filesystem Hierarchy Standard 3.0|title=Chapter 4. The /usr Hierarchy, Section 4.1 Purpose}}</ref>
<!-- ##### /usr is NOT anything but the above. This has been rehashed plenty of times before and reverting misled souls like yourself is taking up roughly a third of every edit on this page (another third being the edits of misled souls such as yourself). This time, Wikipedia is right. ##### -->
|-
|<code>/usr/bin</code>
|Non-essential command [[executable|binaries]] (not needed in [[single-user mode]]); for all users.
|-
|<code>/usr/include</code>
|Standard [[header file|include files]].
|-
|<code>/usr/lib</code>
|[[Library (computer science)|Libraries]] for the [[binaries]] in <code>/usr/bin</code> and <code>/usr/sbin</code>.
|-
|<code>/usr/libexec</code>
|Binaries run by other programs that are not intended to be executed directly by users or shell scripts (optional).
|-
|<code>/usr/lib&lt;qual&gt;</code>
|Alternative-format libraries (e.g., <code>/usr/lib32</code> for 32-bit libraries on a 64-bit machine (optional)).
|-
|<code>/usr/local</code>
|''Tertiary hierarchy'' for local data, specific to this host. Typically has further subdirectories (e.g., <code>bin</code>, <code>lib</code>, <code>share</code>).<ref group="NB">Historically and strictly according to the standard, <code>/usr/local</code> is for data that must be stored on the local host (as opposed to <code>/usr</code>, which may be mounted across a network). Most of the time <code>/usr/local</code> is used for installing software/data that are ''not'' part of the standard operating system distribution (in such case, <code>/usr</code> would only contain software/data that ''are'' part of the standard operating system distribution). It is possible that the FHS standard may in the future be changed to reflect this de facto convention.</ref>
|-
|<code>/usr/sbin</code>
|Non-essential system binaries (e.g., [[Daemon (computer software)|daemons]] for various [[network service]]s).
|-
|<code>/usr/share</code>
|Architecture-independent (shared) data.
|-
|<code>/usr/src</code>
|[[Source code]] (e.g., the kernel source code with its header files).
|-
|<code>/usr/X11R6</code>
|[[X Window System]], Version 11, Release 6 (up to FHS-2.3, optional).
|-
|<code>/var</code>
|Variable files: files whose content is expected to continually change during normal operation of the system, such as logs, spool files, and temporary e-mail files.
|-
|<code>/var/cache</code>
|Application cache data. Such data are locally generated as a result of time-consuming I/O or calculation. The application must be able to regenerate or restore the data. The cached files can be deleted without loss of data.
|-
|<code>/var/lib</code>
|State information. Persistent data modified by programs as they run (e.g., databases, packaging system metadata, etc.).
|-
|<code>/var/lock</code>
|Lock files. Files keeping track of resources currently in use.
|-
|<code>/var/log</code>
|Log files. Various logs.
|-
|<code>/var/mail</code>
|Mailbox files. In some distributions, these files may be located in the deprecated <code>/var/spool/mail</code>.
|-
|<code>/var/opt</code>
|Variable data from add-on packages that are stored in <code>/opt</code>.
|-
|<code>/var/run</code>
|Run-time variable data. This directory contains system information data describing the system since it was booted.<ref>{{cite web |url=https://refspecs.linuxfoundation.org/FHS_2.3/fhs-2.3.html#VARRUNRUNTIMEVARIABLEDATA |title=/var/run : Run-time variable data |work=Filesystem Hierarchy Standard 2.3}}</ref><br />
In FHS 3.0, <code>/var/run</code> is replaced by <code>/run</code>; a system should either continue to provide a <code>/var/run</code> directory or provide a symbolic link from <code>/var/run</code> to <code>/run</code> for backwards compatibility.<ref>{{cite web |url=https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch05s13.html |title=5.13. /var/run : Run-time variable data |work=Filesystem Hierarchy Standard 3.0}}</ref>
|-
|<code>/var/spool</code>
|[[Spooling|Spool]] for tasks waiting to be processed (e.g., print queues and outgoing mail queue).
|-
|<code>/var/spool/mail</code>
|[[Deprecated]] location for users' mailboxes.<ref>{{cite web |title=File System Standard |url=https://refspecs.linuxfoundation.org/FHS_2.3/fhs-2.3.pdf |publisher=Linux Foundation |page=5.11.1}}</ref> 
|-
|<code>/var/tmp</code>
|Temporary files to be preserved between reboots.
|}