file-hierarchy — File system hierarchy overview
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 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.
/¶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 for details).
/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.
/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)
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
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.
Documentation for the operating system or system packages.
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.
Similar to
/usr/share/factory/etc
but for vendor versions of files in
the variable, persistent data
directory
/var.
/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).
/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.
/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.
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. Additional locations for high-level user resources are defined by xdg-user-dirs.
~/.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) list.
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 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).
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.
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/ | 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/ | Private, static vendor resources of the package, including private binaries and libraries, or any other kind of read-only vendor data. |
/usr/lib/ | 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/ | 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/ | 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/ | 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/ | 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/ | 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/ | 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/ | 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/ | 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. |
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/ | 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/ | Private, static vendor resources of the package, compatible with any architecture, or any other kind of read-only vendor data. |
~/.local/lib/ | 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/ | User-specific configuration and state for the package. It is required to default to safe fallbacks if this configuration is missing. |
| User runtime data for the package. |
~/.cache/ | 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. |