Filesystem Hierarchy Standard

The Filesystem Hierarchy Standard (FHS) is a reference that describes the conventions used for the layout of Unix-like systems. It has been made popular by its use in Linux distributions, but it is used by other Unix-like systems as well. The FHS is maintained by the Linux Foundation. The latest version is 3.0, dated March 19, 2015.

Warning
Gentoo DOES NOT adhere to the FHS. Any guidance presented here should be taken as general guidance. The Gentoo Dev Manual and Gentoo Policies are the authoritative source of information on the Gentoo Filesystem layout.

Under the FHS, all files and directories appear under the root directory /, even if they are stored on different physical or virtual devices. Most of these directories exist in all Unix-like operating systems and are generally used in much the same way.

The FHS is intended to support interoperability of applications, system administration tools, development tools, and scripts as well as greater uniformity of documentation for these systems.

Todo:

• Fix "ref" elements, either by creating a Template:Cite web (we may not need that), or changing the "refs"

Standard directories

Directory	Description
/	Primary hierarchy root and root directory of the entire file system hierarchy.
/bin	Essential command binaries that need to be available in single-user mode, including to bring up the system or repair it, for all users (e.g., cat, ls, cp).
/boot	Boot loader files (e.g., kernels, initrd).
/dev	Device file s (e.g., /dev/null, /dev/disk0, /dev/sda1, /dev/tty, /dev/random).
/etc	Host-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, 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). 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".
/etc/opt	Configuration files for add-on packages stored in /opt.
/etc/sgml	Configuration files, such as catalogs, for software that processes SGML.
/etc/X11	Configuration files for the X Window System, version 11.
/etc/xml	Configuration files, such as catalogs, for software that processes XML.
/home	Users' home directories, containing saved files, personal settings, etc.
/lib	Libraries essential for 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.
/media	Mount points for removable media such as CD-ROMs (appeared in FHS-2.3 in 2004).
/mnt	Temporarily mounted filesystems.
/opt	Add-on application software Packages .
/proc	Virtual 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.
/root	root user's home directory.
/run	Run-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).
/sbin	Essential system binaries (e.g., fsck, init, route).
/srv	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).
/sys	Contains information about devices, drivers, and some kernel features.
/tmp	Directory for temporary files (see also /var/tmp). Often not preserved between system reboots and may be severely size-restricted.
/usr	Secondary hierarchy for read-only user data; contains the majority of multi-user utilities and applications. Should be shareable and read-only.
/usr/bin	Non-essential command binaries (not needed in single-user mode); for all users.
/usr/include	Standard include files.
/usr/lib	Libraries for the binaries in /usr/bin and /usr/sbin.
/usr/libexec	Binaries 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/local	Tertiary hierarchy for local data, specific to this host. Typically has further subdirectories (e.g., bin, lib, share).
/usr/sbin	Non-essential system binaries (e.g., daemons for various network services).
/usr/share	Architecture-independent (shared) data.
/usr/src	Source code (e.g., the kernel source code with its header files).
/usr/X11R6	X Window System , Version 11, Release 6 (up to FHS-2.3, optional).
/var	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.
/var/cache	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.
/var/lib	State information. Persistent data modified by programs as they run (e.g., databases, packaging system metadata, etc.).
/var/lock	Lock files. Files keeping track of resources currently in use.
/var/log	Log files. Various logs.
/var/mail	Mailbox files. In some distributions, these files may be located in the deprecated /var/spool/mail.
/var/opt	Variable data from add-on packages that are stored in /opt.
/var/run	Run-time variable data. This directory contains system information data describing the system since it was booted. 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 backwards compatibility.
/var/spool	Spool for tasks waiting to be processed (e.g., print queues and outgoing mail queue).
/var/spool/mail	(Deprecated) location for users' mailboxes.
/var/tmp	Temporary files to be preserved between reboots.

External resources

• https://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.html
• https://wiki.linuxfoundation.org/lsb/fhs
• https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard