file-hierarchy

       Operating systems using the systemd(1) system and service manager are
       organized based on a file system hierarchy inspired by UNIX, more
       specifically the hierarchy described in the File System Hierarchy[1]
       specification and hier(7). This manual page describes a more minimal,
       modernized subset of these specifications that defines more strictly
       the suggestions and restrictions systemd makes on the file system
       hierarchy.

       Many of the paths described here can be queried with the systemd-
       path(1) tool.

GENERAL STRUCTURE
       /
           The file system root. Usually writable, but this is not required.
           Possibly a temporary file system ("tmpfs"). Not shared with other
           hosts (unless read-only).

       /boot
           The boot partition used for bringing up the system. On EFI systems,
           this is possibly the EFI System Partition, also see systemd-gpt-
           auto-generator(8). This directory is usually strictly local to the
           host, and should be considered read-only, except when a new kernel
           or boot loader is installed. This directory only exists on systems
           that run on physical or emulated hardware that requires boot
           loaders.

       /etc
           System-specific configuration. This directory may or may not be
           read-only. Frequently, this directory is pre-populated with
           vendor-supplied configuration files, but applications should not
           make assumptions about this directory being fully populated or
           populated at all, and should fall back to defaults if configuration
           is missing.

       /home
           The location for normal user's home directories. Possibly shared
           with other systems, and never read-only. This directory should only
           be used for normal users, never for system users. This directory
           and possibly the directories contained within it might only become
           available or writable in late boot or even only after user
           authentication. This directory might be placed on
           limited-functionality network file systems, hence applications
           should not assume the full set of file API is available on this
           directory. Applications should generally not reference this
           directory directly, but via the per-user $HOME environment
           variable, or via the home directory field of the user database.

       /root
           The home directory of the root user. The root user's home directory
           is located outside of /home in order to make sure the root user may
           log in even without /home being available and mounted.

       /srv
           The place to store general server payload, managed by the
           Also, files that are not accessed within a certain time are usually
           automatically deleted. If applications find the environment
           variable $TMPDIR set, they should prefer using the directory
           specified in it over directly referencing /tmp (see environ(7) and
           IEEE Std 1003.1[2] for details).

RUNTIME DATA
       /run
           A "tmpfs" file system for system packages to place runtime data in.
           This directory is flushed on boot, and generally writable for
           privileged programs only. Always writable.

       /run/log
           Runtime system logs. System components may place private logs in
           this directory. Always writable, even when /var/log might not be
           accessible yet.

       /run/user
           Contains per-user runtime directories, each usually individually
           mounted "tmpfs" instances. Always writable, flushed at each reboot
           and when the user logs out. User code should not reference this
           directory directly, but via the $XDG_RUNTIME_DIR environment
           variable, as documented in the XDG Base Directory Specification[3].

VENDOR-SUPPLIED OPERATING SYSTEM RESOURCES
       /usr
           Vendor-supplied operating system resources. Usually read-only, but
           this is not required. Possibly shared between multiple hosts. This
           directory should not be modified by the administrator, except when
           installing or removing vendor-supplied packages.

       /usr/bin
           Binaries and executables for user commands that shall appear in the
           $PATH search path. It is recommended not to place binaries in this
           directory that are not useful for invocation from a shell (such as
           daemon binaries); these should be placed in a subdirectory of
           /usr/lib instead.

       /usr/include
           C and C++ API header files of system libraries.

       /usr/lib
           Static, private vendor data that is compatible with all
           architectures (though not necessarily architecture-independent).
           Note that this includes internal executables or other binaries that
           are not regularly invoked from a shell. Such binaries may be for
           any architecture supported by the system. Do not place public
           libraries in this directory, use $libdir (see below), instead.

       /lib/arch-id
           Location for placing dynamic libraries into, also called $libdir.
           The architecture identifier to use is defined on Multiarch
           Architecture Specifiers (Tuples)[4] list. Legacy locations of
           $libdir are /lib, /lib64. This directory should not be used for

       /usr/share/doc
           Documentation for the operating system or system packages.

       /usr/share/factory/etc
           Repository for vendor-supplied default configuration files. This
           directory should be populated with pristine vendor versions of all
           configuration files that may be placed in /etc. This is useful to
           compare the local configuration of a system with vendor defaults
           and to populate the local configuration with defaults.

       /usr/share/factory/var
           Similar to /usr/share/factory/etc, but for vendor versions of files
           in the variable, persistent data directory /var.

PERSISTENT VARIABLE SYSTEM DATA
       /var
           Persistent, variable system data. Must be writable. This directory
           might be pre-populated with vendor-supplied data, but applications
           should be able to reconstruct necessary files and directories in
           this subhierarchy should they be missing, as the system might start
           up without this directory being populated. Persistency is
           recommended, but optional, to support ephemeral systems. This
           directory might become available or writable only very late during
           boot. Components that are required to operate during early boot
           hence shall not unconditionally rely on this directory.

       /var/cache
           Persistent system cache data. System components may place
           non-essential data in this directory. Flushing this directory
           should have no effect on operation of programs, except for
           increased runtimes necessary to rebuild these caches.

       /var/lib
           Persistent system data. System components may place private data in
           this directory.

       /var/log
           Persistent system logs. System components may place private logs in
           this directory, though it is recommended to do most logging via the
           syslog(3) and sd_journal_print(3) calls.

       /var/spool
           Persistent system spool data, such as printer or mail queues.

       /var/tmp
           The place for larger and persistent temporary files. In contrast to
           /tmp, this directory is usually mounted from a persistent physical
           file system and can thus accept larger files. (Use /tmp for smaller
           files.) This directory is generally not flushed at boot-up, but
           time-based cleanup of files that have not been accessed for a
           certain time is applied. The same security restrictions as with
           /tmp apply, and hence only mkstemp(3), mkdtemp(3) or similar calls
           should be used to make use of this directory. If applications find

       /dev/shm
           Place for POSIX shared memory segments, as created via shm_open(3).
           This directory is flushed on boot, and is a "tmpfs" file system.
           Since all users have write access to this directory, special care
           should be taken to avoid name clashes and vulnerabilities. For
           normal users, shared memory segments in this directory are usually
           deleted when the user logs out. Usually, it is a better idea to use
           memory mapped files in /run (for system programs) or
           $XDG_RUNTIME_DIR (for user programs) instead of POSIX shared memory
           segments, since these directories are not world-writable and hence
           not vulnerable to security-sensitive name clashes.

       /proc
           A virtual kernel file system exposing the process list and other
           functionality. This file system is mostly an API to interface with
           the kernel and not a place where normal files may be stored. For
           details, see proc(5). A number of special purpose virtual file
           systems might be mounted below this directory.

       /proc/sys
           A hierarchy below /proc that exposes a number of kernel tunables.
           The primary way to configure the settings in this API file tree is
           via sysctl.d(5) files. In sandboxed/containerized setups, this
           directory is generally mounted read-only.

       /sys
           A virtual kernel file system exposing discovered devices and other
           functionality. This file system is mostly an API to interface with
           the kernel and not a place where normal files may be stored. In
           sandboxed/containerized setups, this directory is generally mounted
           read-only. A number of special purpose virtual file systems might
           be mounted below this directory.

COMPATIBILITY SYMLINKS
       /bin, /sbin, /usr/sbin
           These compatibility symlinks point to /usr/bin, ensuring that
           scripts and binaries referencing these legacy paths correctly find
           their binaries.

       /lib
           This compatibility symlink points to /lib, ensuring that programs
           referencing this legacy path correctly find their resources.

       /lib64
           On some architecture ABIs, this compatibility symlink points to
           $libdir, ensuring that binaries referencing this legacy path
           correctly find their dynamic loader. This symlink only exists on
           architectures whose ABI places the dynamic loader in this path.

       /var/run
           This compatibility symlink points to /run, ensuring that programs
           referencing this legacy path correctly find their runtime data.

           necessary to rebuild these caches. If an application finds
           $XDG_CACHE_HOME set, it should use the directory specified in it
           instead of this directory.

       ~/.config
           Application configuration and state. When a new user is created,
           this directory will be empty or not exist at all. Applications
           should fall back to defaults should their configuration or state in
           this directory be missing. If an application finds $XDG_CONFIG_HOME
           set, it should use the directory specified in it instead of this
           directory.

       ~/.local/bin
           Executables that shall appear in the user's $PATH search path. It
           is recommended not to place executables in this directory that are
           not useful for invocation from a shell; these should be placed in a
           subdirectory of ~/.local/lib instead. Care should be taken when
           placing architecture-dependent binaries in this place, which might
           be problematic if the home directory is shared between multiple
           hosts with different architectures.

       ~/.local/lib
           Static, private vendor data that is compatible with all
           architectures.

       ~/.local/lib/arch-id
           Location for placing public dynamic libraries. The architecture
           identifier to use is defined on Multiarch Architecture Specifiers
           (Tuples)[4] list.

       ~/.local/share
           Resources shared between multiple packages, such as fonts or
           artwork. Usually, the precise location and format of files stored
           below this directory is subject to specifications that ensure
           interoperability. If an application finds $XDG_DATA_HOME set, it
           should use the directory specified in it instead of this directory.

UNPRIVILEGED WRITE ACCESS
       Unprivileged processes generally lack write access to most of the
       hierarchy.

       The exceptions for normal users are /tmp, /var/tmp, /dev/shm, as well
       as the home directory $HOME (usually found below /home) and the runtime
       directory $XDG_RUNTIME_DIR (found below /run/user) of the user, which
       are all writable.

       For unprivileged system processes, only /tmp, /var/tmp and /dev/shm are
       writable. If an unprivileged system process needs a private writable
       directory in /var or /run, it is recommended to either create it before
       dropping privileges in the daemon code, to create it via tmpfiles.d(5)
       fragments during boot, or via the RuntimeDirectory= directive of
       service units (see systemd.unit(5) for details).

NODE TYPES
       recommended locations for specific types of files supplied by the
       vendor.

       Table 1. System Package Vendor Files Locations
       +---------------------+----------------------------+
       |Directory            | Purpose                    |
       +---------------------+----------------------------+
       |/usr/bin             | Package executables that   |
       |                     | shall appear in the $PATH  |
       |                     | executable search path,    |
       |                     | compiled for any of the    |
       |                     | supported architectures    |
       |                     | compatible with the        |
       |                     | operating system. It is    |
       |                     | not recommended to place   |
       |                     | internal binaries or       |
       |                     | binaries that are not      |
       |                     | commonly invoked from the  |
       |                     | shell in this directory,   |
       |                     | such as daemon binaries.   |
       |                     | As this directory is       |
       |                     | shared with most other     |
       |                     | packages of the system,    |
       |                     | special care should be     |
       |                     | taken to pick unique names |
       |                     | for files placed here,     |
       |                     | that are unlikely to clash |
       |                     | with other package's       |
       |                     | files.                     |
       +---------------------+----------------------------+
       |/lib/arch-id         | Public shared libraries of |
       |                     | the package. As above, be  |
       |                     | careful with using too     |
       |                     | generic names, and pick    |
       |                     | unique names for your      |
       |                     | libraries to place here to |
       |                     | avoid name clashes.        |
       +---------------------+----------------------------+
       |/lib/package         | Private static vendor      |
       |                     | resources of the package,  |
       |                     | including private binaries |
       |                     | and libraries, or any      |
       |                     | other kind of read-only    |
       |                     | vendor data.               |
       +---------------------+----------------------------+
       |/lib/arch-id/package | Private other vendor       |
       |                     | resources of the package   |
       |                     | that are                   |
       |                     | architecture-specific and  |
       |                     | cannot be shared between   |
       |                     | architectures. Note that   |
       |                     | this generally does not    |
       |                     | include private            |
       |                     | executables since binaries |
       specifications.

       During runtime, and for local configuration and state, additional
       directories are defined:

       Table 2. System Package Variable Files Locations
       +-------------------+----------------------------+
       |Directory          | Purpose                    |
       +-------------------+----------------------------+
       |/etc/package       | System-specific            |
       |                   | configuration for the      |
       |                   | package. It is recommended |
       |                   | to default to safe         |
       |                   | fallbacks if this          |
       |                   | configuration is missing,  |
       |                   | if this is possible.       |
       |                   | Alternatively, a           |
       |                   | tmpfiles.d(5) fragment may |
       |                   | be used to copy or symlink |
       |                   | the necessary files and    |
       |                   | directories from           |
       |                   | /usr/share/factory during  |
       |                   | boot, via the "L" or "C"   |
       |                   | directives.                |
       +-------------------+----------------------------+
       |/run/package       | Runtime data for the       |
       |                   | package. Packages must be  |
       |                   | able to create the         |
       |                   | necessary subdirectories   |
       |                   | in this tree on their own, |
       |                   | since the directory is     |
       |                   | flushed automatically on   |
       |                   | boot. Alternatively, a     |
       |                   | tmpfiles.d(5) fragment may |
       |                   | be used to create the      |
       |                   | necessary directories      |
       |                   | during boot.               |
       |                   | Alternatively, the         |
       |                   | RuntimeDirectory=          |
       |                   | directive of service units |
       |                   | may be used (see           |
       |                   | systemd.unit(5) for        |
       |                   | details.)                  |
       +-------------------+----------------------------+
       |/run/log/package   | Runtime log data for the   |
       |                   | package. As above, the     |
       |                   | package needs to make sure |
       |                   | to create this directory   |
       |                   | if necessary, as it will   |
       |                   | be flushed on every boot.  |
       +-------------------+----------------------------+
       |/var/cache/package | Persistent cache data of   |
       |                   | the package. If this       |
       |                   | directory is flushed, the  |
       |                   | the package. This is the   |
       |                   | primary place to put       |
       |                   | persistent data that does  |
       |                   | not fall into the other    |
       |                   | categories listed.         |
       |                   | Packages should be able to |
       |                   | create the necessary       |
       |                   | subdirectories in this     |
       |                   | tree on their own, since   |
       |                   | the directory might be     |
       |                   | missing on boot.           |
       |                   | Alternatively, a           |
       |                   | tmpfiles.d(5) fragment may |
       |                   | be used to create the      |
       |                   | necessary directories      |
       |                   | during boot.               |
       +-------------------+----------------------------+
       |/var/log/package   | Persistent log data of the |
       |                   | package. As above, the     |
       |                   | package should make sure   |
       |                   | to create this directory   |
       |                   | if necessary, as it might  |
       |                   | be missing.                |
       +-------------------+----------------------------+
       |/var/spool/package | Persistent spool/queue     |
       |                   | data of the package. As    |
       |                   | above, the package should  |
       |                   | make sure to create this   |
       |                   | directory if necessary, as |
       |                   | it might be missing.       |
       +-------------------+----------------------------+

USER PACKAGES
       Programs running in user context should follow strict rules when
       placing their own files in the user's home directory. The following
       table lists recommended locations in the home directory for specific
       types of files supplied by the vendor if the application is installed
       in the home directory. (Note, however, that user applications installed
       system-wide should follow the rules outlined above regarding placing
       vendor files.)

       Table 3. User Package Vendor File Locations
       +-----------------------------+----------------------------+
       |Directory                    | Purpose                    |
       +-----------------------------+----------------------------+
       |~/.local/bin                 | Package executables that   |
       |                             | shall appear in the $PATH  |
       |                             | executable search path. It |
       |                             | is not recommended to      |
       |                             | place internal executables |
       |                             | or executables that are    |
       |                             | not commonly invoked from  |
       |                             | the shell in this          |
       |                             | directory, such as daemon  |
       |                             | careful with using too     |
       |                             | generic names, and pick    |
       |                             | unique names for your      |
       |                             | libraries to place here to |
       |                             | avoid name clashes.        |
       +-----------------------------+----------------------------+
       |~/.local/lib/package         | Private, static vendor     |
       |                             | resources of the package,  |
       |                             | compatible with any        |
       |                             | architecture, or any other |
       |                             | kind of read-only vendor   |
       |                             | data.                      |
       +-----------------------------+----------------------------+
       |~/.local/lib/arch-id/package | Private other vendor       |
       |                             | resources of the package   |
       |                             | that are                   |
       |                             | architecture-specific and  |
       |                             | cannot be shared between   |
       |                             | architectures.             |
       +-----------------------------+----------------------------+

       Additional static vendor files may be installed in the ~/.local/share
       hierarchy to the locations defined by the various relevant
       specifications.

       During runtime, and for local configuration and state, additional
       directories are defined:

       Table 4. User Package Variable File Locations
       +-------------------------+----------------------------+
       |Directory                | Purpose                    |
       +-------------------------+----------------------------+
       |~/.config/package        | User-specific              |
       |                         | configuration and state    |
       |                         | for the package. It is     |
       |                         | required to default to     |
       |                         | safe fallbacks if this     |
       |                         | configuration is missing.  |
       +-------------------------+----------------------------+
       |$XDG_RUNTIME_DIR/package | User runtime data for the  |
       |                         | package.                   |
       +-------------------------+----------------------------+
       |~/.cache/package         | Persistent cache data of   |
       |                         | the package. If this       |
       |                         | directory is flushed, the  |
       |                         | application should work    |
       |                         | correctly on next          |
       |                         | invocation, though         |
       |                         | possibly slowed down due   |
       |                         | to the need to rebuild any |
       |                         | local cache files. The     |
       |                         | application must be        |
       |                         | capable of recreating this |
       |                         | directory should it be     |
           http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03

        3. XDG Base Directory Specification
           http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html

        4. Multiarch Architecture Specifiers (Tuples)
           https://wiki.debian.org/Multiarch/Tuples

        5. xdg-user-dirs
           http://www.freedesktop.org/wiki/Software/xdg-user-dirs/

systemd 229                                                  FILE-HIERARCHY(7)
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