| FILE-HIERARCHY(7) | file-hierarchy | FILE-HIERARCHY(7) |
NAME¶
file-hierarchy - File system hierarchy overview
DESCRIPTION¶
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 are queriable 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-efi-boot-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
administrator. No restrictions are made how this directory is organized
internally. Generally writable, and possibly shared among systems. This
directory might become available or writable only very late during boot.
/tmp
The place for small temporary files. This directory is
usually mounted as a "tmpfs" instance, and should hence not be used
for larger files. (Use /var/tmp for larger files.) Since the directory is
accessible to other users of the system it is essential that this directory is
only written to with the mkstemp(3), mkdtemp(3) and related
calls. This directory is usually flushed at boot-up. 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.
/usr/lib/arch-id
Location for placing dynamic libraries, also called
$libdir. The architecture identifier to use is defined on Multiarch
Architecture Specifiers (Tuples)[4] list. Legacy locations of
$libdir are /usr/lib, /usr/lib64. This directory should not be used for
package-specific data, unless this data is architecture-dependent, too. To
query $libdir for the primary architecture of the system, invoke:
# pkg-config --variable=libdir
systemd
or
# systemd-path
system-library-arch
/usr/share
Resources shared between multiple packages, such as
documentation, man pages, time zone information, fonts and other resources.
Usually, the precise location and format of files stored below this directory
is subject to specifications that ensure interoperability.
/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 the environment variable $TMPDIR set
they should prefer using the directory specified in it over directly
referencing /var/tmp (see environ(7) for details).
VIRTUAL KERNEL AND API FILE SYSTEMS¶
/dev
The root directory for device nodes. Usually this
directory is mounted as a "devtmpfs" instance, but might be of a
different type in sandboxed/containerized setups. This directory is managed
jointly by the kernel and systemd-udevd(8), and should not be written
to by other components. A number of special purpose virtual file systems might
be mounted below this directory.
/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 those
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 /usr/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.
HOME DIRECTORY¶
User applications may want to place files and directories in the user's home directory. They should follow the following basic structure. Note that some of these directories are also standardized (though more weakly) by the XDG Base Directory Specification[3]. Additional locations for high-level user resources are defined by xdg-user-dirs[5].
~/.cache
Persistent user cache data. User programs 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. If an application finds $XDG_CACHE_HOME set is
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 is 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 is 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¶
Unix file systems support different types of file nodes, including regular files, directories, symlinks, character and block device nodes, sockets and FIFOs.
It is strongly recommended that /dev is the only location below which device nodes shall be placed. Similar, /run shall be the only location to place sockets and FIFOs. Regular files, directories and symlinks may be used in all directories.
SYSTEM PACKAGES¶
Developers of system packages should follow strict rules when placing their own files in the file system. The following table lists 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. |
| /usr/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. |
| /usr/lib/package | Private, static vendor resources of the package, including private binaries and libraries, or any other kind of read-only vendor data. |
| /usr/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 of a specific architecture may be freely invoked from any other supported system architecture. |
| /usr/include/package | Public C/C++ APIs of public shared libraries of the package. |
Additional static vendor files may be installed in the
/usr/share hierarchy, to the locations defined by the various relevant
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 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 missing and necessary. |
| /var/lib/package | Persistent private data of 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 executables. As this directory is shared with most other packages of the user special care should be taken to pick unique names for files placed here, that are unlikely to clash with other package's files. |
| ~/.local/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. |
| ~/.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 missing and necessary. |
SEE ALSO¶
systemd(1),
hier(7), systemd-path(1), systemd-efi-boot-generator(8),
sysctl.d(5), tmpfiles.d(5), pkg-config(1),
systemd.unit(5)
NOTES¶
- 1.
- File System Hierarchy
- 2.
- IEEE Std 1003.1
- 3.
- XDG Base Directory Specification
- 4.
- Multiarch Architecture Specifiers (Tuples)
- 5.
- xdg-user-dirs
| systemd 219 |