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04-E.12.1: Linux Directory Structure - Hierarchy

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    Filesystem Hierarchy Standard

    The Filesystem Hierarchy Standard (FHS) defines the directory structure and directory contents in Linux distributions. It is maintained by the Linux Foundation. The latest version is 3.0, and was released on 3 June 2015.

    The video discusses the Filesystem Hierarchy Standard and explains what it means.

    Directory Structure

    In the FHS, all files and directories appear under the root directory / , even if they are stored on different physical or virtual devices. Some of these directories only exist on 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.

    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; for all users, e.g., cat, ls, cp.
    /boot Boot loader files, e.g., kernels, initrd.
    /dev Device files, 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 acronyms such as "Editable Text Configuration" or "Extended Tool Chest."

    /etc/opt Configuration files for add-on packages that are 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 the binaries in /bin and /sbin .
    /lib<qual> Alternative format essential libraries. 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 Optional 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 Home directory for the root user.
    /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 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.
    /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/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.

    In a pictorial manner, here is what the filesystem looks like. Some of these directories have standard files as well - /bin, /etc and /sbin specifically.

    Standard Unix Filesystem Hierarchy showing the usual placement of files across the entire system.
    Figure \(\PageIndex{1}\): Standard-unix-filesystem-hierarchy. ("Standard-unix-filesystem-hierarchy.svg" by PpgardneWikimedia Commons is licensed under CC BY-SA 4.0)

    Adapted from:
    "Filesystem Hierarchy Standard" by Multiple contributors, Wikipedia is licensed under CC BY-SA 4.0

    04-E.12.1: Linux Directory Structure - Hierarchy is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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