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), with various extensions, partially documented
in the XDG Base Directory Specification[2] and XDG User Directories[3].
This manual page describes a more generalized, though minimal and
modernized subset of these specifications that defines more strictly the
suggestions and restrictions systemd makes on the file system hierarchy.
Note that this document makes no attempt to define the directory
structure comprehensively, it only documents a skeleton of a directory
tree, that downstreams can extend. Because of that traditional
directories such as /usr/include/ or /var/spool/ are not covered, even
though it might (or might not) make a lot of sense to include them in
the structure of an actually deployed OS.
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 (ESP), 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.
/efi/
If the boot partition /boot/ is maintained separately from the EFI
System Partition (ESP), the latter is mounted here. Tools that need
to operate on the EFI system partition should look for it at this
mount point first, and fall back to /boot/ — if the former does not
qualify (for example if it is not a mount point or does not have the
correct file system type MSDOS_SUPER_MAGIC).
/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.) This directory is
usually flushed at boot-up. Also, files that are not accessed within
a certain time may be automatically deleted.
If applications find the environment variable $TMPDIR set, they
should use the directory specified in it instead of /tmp/ (see
environ(7) and IEEE Std 1003.1[4] for details).
Since /tmp/ is accessible to other users of the system, it is
essential that files and subdirectories under this directory are
only created with mkstemp(3), mkdtemp(3), and similar calls. For
more details, see Using /tmp/ and /var/tmp/ Safely[5].
RUNTIME DATA
/run/
A "tmpfs" file system for system packages to place runtime data,
socket files, and similar. 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[2].
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/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 into, also called $libdir.
The architecture identifier to use is defined on Multiarch
Architecture Specifiers (Tuples)[6] 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:
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.
Note that resources placed in this directory typically are under
shared ownership, i.e. multiple different packages have provided and
consumed these resources, on equal footing, without any obvious
primary owner. This makes things systematically different from
/usr/lib/, where ownership is generally not shared.
/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. Writable during normal system
operation. 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/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 small
ephemeral 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.
If applications find the environment variable $TMPDIR set, they
should use the directory specified in it instead of /var/tmp/ (see
environ(7) for details).
The same security restrictions as with /tmp/ apply: mkstemp(3),
mkdtemp(3), and similar calls should be used. For further details
about this directory, see Using /tmp/ and /var/tmp/ Safely[5].
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 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.
/sys/fs/cgroup/
A virtual kernel file system exposing process control groups
(cgroups). This file system is an API to interface with the kernel
and not a place where normal files may be stored. On current systems
running in the default "unified" mode, this directory serves as the
mount point for the "cgroup2" filesystem, which provides a unified
cgroup hierarchy for all resource controllers. On systems with
non-default configurations, this directory may instead be a tmpfs
filesystem containing mount points for various "cgroup" (v1)
resource controllers; in such configurations, if "cgroup2" is
mounted it will be mounted on /sys/fs/cgroup/unified/, but cgroup2
will not have resource controllers attached. In
sandboxed/containerized setups, this directory may either not exist
or may include a subset of functionality.
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[2]. Additional locations
for high-level user resources are defined by xdg-user-dirs[3].
~/.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, it should use the directory specified in it
instead of this directory.
~/.config/
Application configuration. 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 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)[6] 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.
~/.local/state/
Application 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 state in this directory be missing. If an
application finds $XDG_STATE_HOME set, it should use the directory
specified in it instead of this directory.
WRITE ACCESS
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 StateDirectory= and
RuntimeDirectory= directives of service units (see systemd.unit(5) for
details).
/tmp/, /var/tmp/ and /dev/shm/ should be mounted nosuid and nodev, which
means that set-user-id mode and character or block special devices are
not interpreted on those file systems. In general it is not possible to
mount them noexec, because various programs use those directories for
dynamically generated or optimized code, and with that flag those use
cases would break. Using this flag is OK on special-purpose
installations or systems where all software that may be installed is
known and does not require such functionality. See the discussion of
nosuid/nodev/noexec in mount(8) and PROT_EXEC in mmap(2).
Lack of Write Access on Read-Only Systems and during System Recovery
As noted above, some systems operate with the /usr and /etc hierarchies
mounted read-only, possibly only allowing write access during package
upgrades. Other part of the hierarchy are generally mounted read-write
(in particular /var and /var/tmp), but may be read-only when the kernel
remounts the file system read-only in response to errors, or when the
system is booted read-only for recovery purposes. To the extent
reasonable, applications should be prepared to execute without write
access, so that for example, failure to save non-essential data to
/var/cache/ or failure to create a custom log file under /var/log does
not prevent the application from running.
The /run/ directory is available since the earliest boot and is always
writable. It should be used for any runtime data and sockets, so that
write access to e.g. /etc or /var is not needed.
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. Similarly, /run/ shall be the only
location to place sockets and FIFOs. Regular files, directories and
symlinks may be used in all directories.
Applications should expect that a security policy might be enforced on a
system that enforces these rules.
SYSTEM PACKAGES
Developers of system packages should follow strict rules when placing
their 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. │
└───────────────────────────┴────────────────────────────┘
Additional static vendor files with shared ownership may be installed in
the /usr/share/ hierarchy to the locations defined by the various
relevant specifications.
The following directories shall be used by the package for local
configuration and files created during runtime:
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, or the │
│ │ RuntimeDirectory= │
│ │ directive of service units │
│ │ may be used to create them │
│ │ at service startup (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. To │
│ │ create an empty directory, │
│ │ a tmpfiles.d(5) fragment │
│ │ or the CacheDirectory= │
│ │ directive of service units │
│ │ (see systemd.unit(5)) may │
│ │ be used. │
├─────────────────────┼────────────────────────────┤
│ /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. To create │
│ │ an empty directory, a │
│ │ tmpfiles.d(5) fragment or │
│ │ the StateDirectory= │
│ │ directive of service units │
│ │ (see systemd.unit(5)) may │
│ │ be used. │
├─────────────────────┼────────────────────────────┤
│ /var/log/package/ │ Persistent log data of the │
│ │ package. As above, the │
│ │ package should make sure │
│ │ to create this directory │
│ │ if necessary, possibly │
│ │ using tmpfiles.d(5) or │
│ │ LogsDirectory= (see │
│ │ systemd.exec(5)), 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. (User applications installed system-wide are covered by the
rules outlined above for vendor files.)
Table 3. Vendor package file locations under the home directory of the
user
┌───────────────────────────────┬────────────────────────────┐
│ 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 overly │
│ │ 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 with shared ownership may be installed in
the ~/.local/share/ hierarchy, mirroring the subdirectories specified in
the section "Vendor-supplied operating system resources" above.
The following directories shall be used by the package for per-user
local configuration and files created during runtime:
Table 4. User package variable file locations
┌───────────────────────────┬────────────────────────────┐
│ Directory │ Purpose │
├───────────────────────────┼────────────────────────────┤
│ ~/.config/package/ │ User-specific │
│ │ configuration 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. │
├───────────────────────────┼────────────────────────────┤
│ ~/.local/state/package/ │ Persistent state data of │
│ │ the package. │
└───────────────────────────┴────────────────────────────┘
SEE ALSO
systemd(1), hier(7), systemd-path(1), systemd-gpt-auto-generator(8),
sysctl.d(5), tmpfiles.d(5), pkg-config(1), systemd.unit(5)
NOTES
1. File System Hierarchy
http://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.html
2. XDG Base Directory Specification
https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
3. XDG User Directories
https://www.freedesktop.org/wiki/Software/xdg-user-dirs
4. IEEE Std 1003.1
http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03
5. Using /tmp/ and /var/tmp/ Safely
https://systemd.io/TEMPORARY_DIRECTORIES
6. Multiarch Architecture Specifiers (Tuples)
https://wiki.debian.org/Multiarch/Tuples
systemd 257.9 FILE-HIERARCHY(7)
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