⏾ Concept Map

❪◑❫ Unix Directories ○｜_append｜___｜20261013195257-02-•

DirectoryDescription
/Primary hierarchy root and root directory of the entire file system hierarchy.
/binEssential command binaries that need to be available in single-user mode, including to bring up the system or repair it,12 for all users (e.g., cat, ls, cp).
/bootBoot loader files (e.g., kernels, initrd).
/devDevice files (e.g., /dev/null, /dev/disk0, /dev/sda1, /dev/tty, /dev/random).
/etcHost-specific system-wide configuration files.
There has been controversy over the meaning of the name itself. In early versions of the UNIX Implementation Document from Bell Labs, /etc is referred to as the etcetera directory,3 as this directory historically held everything that did not belong elsewhere (however, the FHS restricts /etc to static configuration files and may not contain binaries).4 Since the publication of early documentation, the directory name has been re-explained in various ways. Later interpretations include backronyms such as “Editable Text Configuration” or “Extended Tool Chest”.5
/etc/optConfiguration files for add-on packages stored in /opt.
/etc/sgmlConfiguration files, such as catalogs, for software that processes SGML.
/etc/X11Configuration files for the X Window System, version 11.
/etc/xmlConfiguration files, such as catalogs, for software that processes XML.
/homeUsers’ home directories, containing saved files, personal settings, etc.
/libLibraries essential for the binaries in /bin and /sbin.
/lib<qual>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.
/mediaMount points for removable media such as CD-ROMs (appeared in FHS-2.3 in 2004).
/mntTemporarily mounted filesystems.
/optAdd-on application software packages.6
/procVirtual filesystem providing process and kernel information as files. In Linux, corresponds to a procfs mount. Generally, automatically generated and populated by the system, on the fly.
/rootHome directory for the root user.
/runRun-time variable data: Information about the running system since last boot, e.g., currently logged-in users and running 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).
/sbinEssential system binaries (e.g., fsck, init, route).
/srvSite-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).
/sysContains information about devices, drivers, and some kernel features.7
/tmpDirectory for temporary files (see also /var/tmp). Often not preserved between system reboots and may be severely size-restricted.
/usrSecondary hierarchy for read-only user data; contains the majority of (multi-)user utilities and applications.8 Should be shareable and read-only.910
/usr/binNon-essential command binaries (not needed in single-user mode); for all users.
/usr/includeStandard include files.
/usr/libLibraries for the binaries in /usr/bin and /usr/sbin.
/usr/libexecBinaries run by other programs that are not intended to be executed directly by users or shell scripts (optional).
/usr/lib<qual>Alternative-format libraries (e.g., /usr/lib32 for 32-bit libraries on a 64-bit machine (optional)).
/usr/localTertiary hierarchy for local data, specific to this host. Typically has further subdirectories (e.g., bin, lib, share).11
/usr/sbinNon-essential system binaries (e.g., daemons for various network services).
/usr/shareArchitecture-independent (shared) data.
/usr/srcSource code (e.g., the kernel source code with its header files).
/usr/X11R6X Window System, Version 11, Release 6 (up to FHS-2.3, optional).
/varVariable 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.
/var/cacheApplication 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.
/var/libState information. Persistent data modified by programs as they run (e.g., databases, packaging system metadata, etc.).
/var/lockLock files. Files keeping track of resources currently in use.
/var/logLog files. Various logs.
/var/mailMailbox files. In some distributions, these files may be located in the deprecated /var/spool/mail.
/var/optVariable data from add-on packages that are stored in /opt.
/var/runRun-time variable data. This directory contains system information data describing the system since it was booted.12
In FHS 3.0, /var/run is replaced by /run; a system should either continue to provide a /var/run directory or provide a symbolic link from /var/run to /run for backward compatibility.13
/var/spoolSpool for tasks waiting to be processed (e.g., print queues and outgoing mail queue). Formerly also contained user mailbox files at /var/spool/mail.14
/var/tmpTemporary files to be preserved between reboots.

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Footnotes

  1. “hier(7)”. man7.org. Retrieved 6 January 2021. ↩

  2. hier(7) – Linux Programmer’s Manual – Overview, Conventions and Miscellanea from Manned.org ↩

  3. DeFelice, J. (17 March 1972). “E.0”. Preliminary Release of UNIX Implementation Document (PDF). p. 8. IMO.1-1. Retrieved 6 June 2024. ↩

  4. “/etc: Host-specific system configuration”. Filesystem Hierarchy Standard 2.3. Retrieved 18 February 2016. ↩

  5. Cliff (3 March 2007). “Define -/etc?”. ask.slashdot.org. Retrieved 5 October 2025. ↩

  6. “/opt: Add-on application software packages”. Filesystem Hierarchy Standard 2.3. Retrieved 18 February 2016. ↩

  7. “/sys: Kernel and system information virtual filesystem”. Filesystem Hierarchy Standard 3.0. Retrieved 4 June 2017. ↩

  8. The name is historical, and dates back to when /usr was used for user home directories on Unix; see the entry for /usr in the table in Unix filesystem § Conventional directory layout. ↩

  9. “Chapter 4. The/usr Hierarchy”. Filesystem Hierarchy Standard 2.3. Retrieved 5 October 2025. ↩

  10. “Chapter 4. The/usr Hierarchy, Section 4.1 Purpose”. Filesystem Hierarchy Standard 3.0. Retrieved 5 October 2025. ↩

  11. Historically and strictly according to the standard, /usr/local is for data that must be stored on the local host (as opposed to /usr, which may be mounted across a network). Most of the time /usr/local is used for installing software/data that are not part of the standard operating system distribution (in such case, /usr 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. ↩

  12. “/var/run: Run-time variable data”. Filesystem Hierarchy Standard 2.3. Retrieved 5 October 2025. ↩

  13. “5.13./var/run: Run-time variable data”. Filesystem Hierarchy Standard 3.0. Retrieved 5 October 2025. ↩

  14. “File System Standard” (PDF). Linux Foundation. 5.11.1. Purpose. Retrieved 5 October 2025. ↩