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 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
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.
/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
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.
/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 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.
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, 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
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.
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.
/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
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-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_2.3/fhs-2.3.html
2. IEEE Std 1003.1
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/
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