systemd/man/file-hierarchy.xml
2023-12-25 15:51:47 +01:00

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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="file-hierarchy" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>file-hierarchy</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>file-hierarchy</refentrytitle>
<manvolnum>7</manvolnum>
</refmeta>
<refnamediv>
<refname>file-hierarchy</refname>
<refpurpose>File system hierarchy overview</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<para>Operating systems using the
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> system and service
manager are organized based on a file system hierarchy inspired by UNIX, more specifically the hierarchy described
in the <ulink url="http://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.html">File System Hierarchy</ulink>
specification and <citerefentry
project='man-pages'><refentrytitle>hier</refentrytitle><manvolnum>7</manvolnum></citerefentry>, with various
extensions, partially documented in the <ulink
url="https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG Base Directory
Specification</ulink> and <ulink url="https://www.freedesktop.org/wiki/Software/xdg-user-dirs">XDG User
Directories</ulink>. 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.</para>
<para>Many of the paths described here can be queried
with the
<citerefentry><refentrytitle>systemd-path</refentrytitle><manvolnum>1</manvolnum></citerefentry>
tool.</para>
</refsect1>
<refsect1>
<title>General Structure</title>
<variablelist>
<varlistentry>
<term><filename>/</filename></term>
<listitem><para>The file system root. Usually writable, but
this is not required. Possibly a temporary file system
(<literal>tmpfs</literal>). Not shared with other hosts
(unless read-only). </para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/boot/</filename></term>
<listitem><para>The boot partition used for bringing up the
system. On EFI systems, this is possibly the EFI System
Partition (ESP), also see
<citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
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.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/efi/</filename></term>
<listitem><para>If the boot partition <filename>/boot/</filename> 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 <filename>/boot/</filename> — if the former doesn't qualify
(for example if it is not a mount point or does not have the correct file system type
<constant>MSDOS_SUPER_MAGIC</constant>).</para>
<xi:include href="version-info.xml" xpointer="v239"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/etc/</filename></term>
<listitem><para>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.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/home/</filename></term>
<listitem><para>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 <varname>$HOME</varname>
environment variable, or via the home directory field of the
user database.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/root/</filename></term>
<listitem><para>The home directory of the root user. The root
user's home directory is located outside of
<filename>/home/</filename> in order to make sure the root user
may log in even without <filename>/home/</filename> being
available and mounted.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/srv/</filename></term>
<listitem><para>The place to store general server payload,
managed by the administrator. No restrictions are made how
this directory is organized internally. Generally writable,
and possibly shared among systems. This directory might become
available or writable only very late during
boot.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/tmp/</filename></term>
<listitem><para>The place for small temporary files. This directory is usually mounted as a
<literal>tmpfs</literal> instance, and should hence not be used for larger files. (Use
<filename>/var/tmp/</filename> for larger files.) This directory is usually flushed at boot-up. Also,
files that are not accessed within a certain time may be automatically deleted.</para>
<para>If applications find the environment variable <varname>$TMPDIR</varname> set, they should use
the directory specified in it instead of <filename>/tmp/</filename> (see <citerefentry
project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry> and
<ulink url="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03">IEEE
Std 1003.1</ulink> for details).</para>
<para>Since <filename>/tmp/</filename> is accessible to other users of the system, it is essential
that files and subdirectories under this directory are only created with <citerefentry
project='man-pages'><refentrytitle>mkstemp</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry
project='man-pages'><refentrytitle>mkdtemp</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
and similar calls. For more details, see <ulink url="https://systemd.io/TEMPORARY_DIRECTORIES">Using
/tmp/ and /var/tmp/ Safely</ulink>.</para>
<xi:include href="version-info.xml" xpointer="v215"/>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Runtime Data</title>
<variablelist>
<varlistentry>
<term><filename>/run/</filename></term>
<listitem><para>A <literal>tmpfs</literal> 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.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/run/log/</filename></term>
<listitem><para>Runtime system logs. System components may
place private logs in this directory. Always writable, even
when <filename>/var/log/</filename> might not be accessible
yet.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/run/user/</filename></term>
<listitem><para>Contains per-user runtime directories, each
usually individually mounted <literal>tmpfs</literal>
instances. Always writable, flushed at each reboot and when
the user logs out. User code should not reference this
directory directly, but via the
<varname>$XDG_RUNTIME_DIR</varname> environment variable, as
documented in the <ulink
url="https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
Base Directory Specification</ulink>.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Vendor-supplied Operating System Resources</title>
<variablelist>
<varlistentry>
<term><filename>/usr/</filename></term>
<listitem><para>Vendor-supplied operating system resources.
Usually read-only, but this is not required. Possibly shared
between multiple hosts. This directory should not be modified
by the administrator, except when installing or removing
vendor-supplied packages.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/usr/bin/</filename></term>
<listitem><para>Binaries and executables for user commands
that shall appear in the <varname>$PATH</varname> 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
<filename>/usr/lib/</filename> instead.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/usr/include/</filename></term>
<listitem><para>C and C++ API header files of system
libraries.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/usr/lib/</filename></term>
<listitem><para>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 <varname>$libdir</varname> (see below),
instead.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/usr/lib/<replaceable>arch-id</replaceable>/</filename></term>
<listitem><para>Location for placing dynamic libraries into, also
called <varname>$libdir</varname>. The architecture identifier
to use is defined on <ulink
url="https://wiki.debian.org/Multiarch/Tuples">Multiarch
Architecture Specifiers (Tuples)</ulink> list. Legacy
locations of <varname>$libdir</varname> are
<filename>/usr/lib/</filename>,
<filename>/usr/lib64/</filename>. This directory should not be
used for package-specific data, unless this data is
architecture-dependent, too. To query
<varname>$libdir</varname> for the primary architecture of the
system, invoke:
<programlisting># systemd-path system-library-arch</programlisting></para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/usr/share/</filename></term>
<listitem><para>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.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/usr/share/doc/</filename></term>
<listitem><para>Documentation for the operating system or
system packages.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/usr/share/factory/etc/</filename></term>
<listitem><para>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 <filename>/etc/</filename>. This is useful to
compare the local configuration of a system with vendor
defaults and to populate the local configuration with
defaults.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/usr/share/factory/var/</filename></term>
<listitem><para>Similar to
<filename>/usr/share/factory/etc/</filename>, but for vendor
versions of files in the variable, persistent data directory
<filename>/var/</filename>.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Persistent Variable System Data</title>
<variablelist>
<varlistentry>
<term><filename>/var/</filename></term>
<listitem><para>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.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/var/cache/</filename></term>
<listitem><para>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.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/var/lib/</filename></term>
<listitem><para>Persistent system data. System components may
place private data in this directory.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/var/log/</filename></term>
<listitem><para>Persistent system logs. System components may
place private logs in this directory, though it is recommended
to do most logging via the
<citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>
calls.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/var/spool/</filename></term>
<listitem><para>Persistent system spool data, such as printer
or mail queues.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/var/tmp/</filename></term>
<listitem><para>The place for larger and persistent temporary files. In contrast to
<filename>/tmp/</filename>, this directory is usually mounted from a persistent physical file system
and can thus accept larger files. (Use <filename>/tmp/</filename> 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.</para>
<para>If applications find the environment variable <varname>$TMPDIR</varname> set, they should use
the directory specified in it instead of <filename>/var/tmp/</filename> (see <citerefentry
project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
details).</para>
<para>The same security restrictions as with <filename>/tmp/</filename> apply: <citerefentry
project='man-pages'><refentrytitle>mkstemp</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry
project='man-pages'><refentrytitle>mkdtemp</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
and similar calls should be used. For further details about this directory, see <ulink
url="https://systemd.io/TEMPORARY_DIRECTORIES">Using /tmp/ and /var/tmp/ Safely</ulink>.</para>
<xi:include href="version-info.xml" xpointer="v215"/>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Virtual Kernel and API File Systems</title>
<variablelist>
<varlistentry>
<term><filename>/dev/</filename></term>
<listitem><para>The root directory for device nodes. Usually,
this directory is mounted as a <literal>devtmpfs</literal>
instance, but might be of a different type in
sandboxed/containerized setups. This directory is managed
jointly by the kernel and
<citerefentry><refentrytitle>systemd-udevd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
and should not be written to by other components. A number of
special purpose virtual file systems might be mounted below
this directory.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/dev/shm/</filename></term>
<listitem><para>Place for POSIX shared memory segments, as
created via
<citerefentry project='die-net'><refentrytitle>shm_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
This directory is flushed on boot, and is a
<literal>tmpfs</literal> 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 <filename>/run/</filename> (for system
programs) or <varname>$XDG_RUNTIME_DIR</varname> (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.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/proc/</filename></term>
<listitem><para>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
<citerefentry project='man-pages'><refentrytitle>proc</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
A number of special purpose virtual file systems might be
mounted below this directory.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/proc/sys/</filename></term>
<listitem><para>A hierarchy below <filename>/proc/</filename>
that exposes a number of kernel tunables. The primary way to
configure the settings in this API file tree is via
<citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
files. In sandboxed/containerized setups, this directory is
generally mounted read-only.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/sys/</filename></term>
<listitem><para>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.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/sys/fs/cgroup/</filename></term>
<listitem><para>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
<literal>cgroup2</literal> 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
<literal>cgroup</literal> (v1) resource controllers; in such
configurations, if <literal>cgroup2</literal> is mounted it will be
mounted on <filename>/sys/fs/cgroup/unified/</filename>, 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.
</para>
<xi:include href="version-info.xml" xpointer="v251"/></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Compatibility Symlinks</title>
<variablelist>
<varlistentry>
<term><filename>/bin/</filename></term>
<term><filename>/sbin/</filename></term>
<term><filename>/usr/sbin/</filename></term>
<listitem><para>These compatibility symlinks point to
<filename>/usr/bin/</filename>, ensuring that scripts and
binaries referencing these legacy paths correctly find their
binaries.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/lib/</filename></term>
<listitem><para>This compatibility symlink points to
<filename>/usr/lib/</filename>, ensuring that programs
referencing this legacy path correctly find their
resources.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/lib64/</filename></term>
<listitem><para>On some architecture ABIs, this compatibility
symlink points to <varname>$libdir</varname>, ensuring that
binaries referencing this legacy path correctly find their
dynamic loader. This symlink only exists on architectures
whose ABI places the dynamic loader in this
path.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>/var/run/</filename></term>
<listitem><para>This compatibility symlink points to
<filename>/run/</filename>, ensuring that programs referencing
this legacy path correctly find their runtime
data.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Home Directory</title>
<para>User applications may want to place files and directories in
the user's home directory. They should follow the following basic
structure. Note that some of these directories are also
standardized (though more weakly) by the <ulink
url="https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
Base Directory Specification</ulink>. Additional locations for
high-level user resources are defined by <ulink
url="https://www.freedesktop.org/wiki/Software/xdg-user-dirs">xdg-user-dirs</ulink>.</para>
<variablelist>
<varlistentry>
<term><filename>~/.cache/</filename></term>
<listitem><para>Persistent user cache data. User programs may place non-essential data in this
directory. Flushing this directory should have no effect on operation of programs, except for
increased runtimes necessary to rebuild these caches. If an application finds
<varname>$XDG_CACHE_HOME</varname> set, it should use the directory specified in it instead of this
directory.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>~/.config/</filename></term>
<listitem><para>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 <varname>$XDG_CONFIG_HOME</varname> set, it should use
the directory specified in it instead of this directory.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>~/.local/bin/</filename></term>
<listitem><para>Executables that shall appear in the user's <varname>$PATH</varname> 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 <filename>~/.local/lib/</filename> 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.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>~/.local/lib/</filename></term>
<listitem><para>Static, private vendor data that is compatible with all
architectures.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>~/.local/lib/<replaceable>arch-id</replaceable>/</filename></term>
<listitem><para>Location for placing public dynamic libraries. The architecture identifier to use is
defined on <ulink url="https://wiki.debian.org/Multiarch/Tuples">Multiarch Architecture Specifiers
(Tuples)</ulink> list.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>~/.local/share/</filename></term>
<listitem><para>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 <varname>$XDG_DATA_HOME</varname> set, it should use
the directory specified in it instead of this directory.</para>
<xi:include href="version-info.xml" xpointer="v215"/></listitem>
</varlistentry>
<varlistentry>
<term><filename>~/.local/state/</filename></term>
<listitem><para>Application state. When a new user is created, this directory will be empty or not
exist at all. Applications should fall back to defaults should their state in this directory be
missing. If an application finds <varname>$XDG_STATE_HOME</varname> set, it should use the directory
specified in it instead of this directory.</para>
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Write Access</title>
<refsect2>
<title>Unprivileged Write Access</title>
<para>Unprivileged processes generally lack write access to most of the hierarchy.</para>
<para>The exceptions for normal users are
<filename>/tmp/</filename>,
<filename>/var/tmp/</filename>,
<filename>/dev/shm/</filename>, as well as the home directory
<varname>$HOME</varname> (usually found below
<filename>/home/</filename>) and the runtime directory
<varname>$XDG_RUNTIME_DIR</varname> (found below
<filename>/run/user/</filename>) of the user, which are all
writable.</para>
<para>For unprivileged system processes, only
<filename>/tmp/</filename>,
<filename>/var/tmp/</filename> and
<filename>/dev/shm/</filename> are writable. If an
unprivileged system process needs a private writable directory in
<filename>/var/</filename> or <filename>/run/</filename>, it is
recommended to either create it before dropping privileges in the
daemon code, to create it via
<citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
fragments during boot, or via the
<varname>StateDirectory=</varname> and <varname>RuntimeDirectory=</varname>
directives of service units (see
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details).</para>
<para><filename>/tmp/</filename>, <filename>/var/tmp/</filename> and <filename>/dev/shm/</filename>
should be mounted <option>nosuid</option> and <option>nodev</option>, 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 <option>noexec</option>, 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 doesn't require such functionality. See the discussion of
<option>nosuid</option>/<option>nodev</option>/<option>noexec</option> in <citerefentry
project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry> and
<constant>PROT_EXEC</constant> in <citerefentry
project='man-pages'><refentrytitle>mmap</refentrytitle><manvolnum>2</manvolnum></citerefentry>.
</para>
</refsect2>
<refsect2>
<title>Lack of Write Access on Read-Only Systems and during System Recovery</title>
<para>As noted above, some systems operate with the <filename>/usr</filename> and
<filename>/etc</filename> hierarchies mounted read-only, possibly only allowing write access during
package upgrades. Other part of the hierarchy are generally mounted read-write (in particular
<filename>/var</filename> and <filename>/var/tmp</filename>), 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 <filename>/var/cache/</filename> or
failure to create a custom log file under <filename>/var/log</filename> does not prevent the
application from running.</para>
<para>The <filename>/run/</filename> 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.
<filename>/etc</filename> or <filename>/var</filename> is not needed.</para>
</refsect2>
</refsect1>
<refsect1>
<title>Node Types</title>
<para>Unix file systems support different types of file nodes,
including regular files, directories, symlinks, character and
block device nodes, sockets and FIFOs.</para>
<para>It is strongly recommended that <filename>/dev/</filename> is
the only location below which device nodes shall be placed.
Similarly, <filename>/run/</filename> shall be the only location to
place sockets and FIFOs. Regular files, directories and symlinks
may be used in all directories.</para>
</refsect1>
<refsect1>
<title>System Packages</title>
<para>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.</para>
<table>
<title>System package vendor files locations</title>
<tgroup cols='2' align='left' colsep='1' rowsep='1'>
<colspec colname="directory" />
<colspec colname="purpose" />
<thead>
<row>
<entry>Directory</entry>
<entry>Purpose</entry>
</row>
</thead>
<tbody>
<row>
<entry><filename>/usr/bin/</filename></entry>
<entry>Package executables that shall appear in the <varname>$PATH</varname> 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.</entry>
</row>
<row>
<entry><filename>/usr/lib/<replaceable>arch-id</replaceable>/</filename></entry>
<entry>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.</entry>
</row>
<row>
<entry><filename>/usr/lib/<replaceable>package</replaceable>/</filename></entry>
<entry>Private static vendor resources of the package, including private binaries and libraries, or any other kind of read-only vendor data.</entry>
</row>
<row>
<entry><filename>/usr/lib/<replaceable>arch-id</replaceable>/<replaceable>package</replaceable>/</filename></entry>
<entry>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.</entry>
</row>
<row>
<entry><filename>/usr/include/<replaceable>package</replaceable>/</filename></entry>
<entry>Public C/C++ APIs of public shared libraries of the package.</entry>
</row>
</tbody>
</tgroup>
</table>
<para>Additional static vendor files may be installed in the
<filename>/usr/share/</filename> hierarchy to the locations
defined by the various relevant specifications.</para>
<para>The following directories shall be used by the package for local configuration and files created
during runtime:</para>
<table>
<title>System package variable files locations</title>
<tgroup cols='2' align='left' colsep='1' rowsep='1'>
<colspec colname="directory" />
<colspec colname="purpose" />
<thead>
<row>
<entry>Directory</entry>
<entry>Purpose</entry>
</row>
</thead>
<tbody>
<row>
<entry><filename>/etc/<replaceable>package</replaceable>/</filename></entry>
<entry>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 <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> fragment may be used to copy or symlink the necessary files and directories from <filename>/usr/share/factory/</filename> during boot, via the <literal>L</literal> or <literal>C</literal> directives.</entry>
</row>
<row>
<entry><filename>/run/<replaceable>package</replaceable>/</filename></entry>
<entry>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 <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> fragment may be used to create the necessary directories during boot, or the <varname>RuntimeDirectory=</varname> directive of service units may be used to create them at service startup (see <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details).</entry>
</row>
<row>
<entry><filename>/run/log/<replaceable>package</replaceable>/</filename></entry>
<entry>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.</entry>
</row>
<row>
<entry><filename>/var/cache/<replaceable>package</replaceable>/</filename></entry>
<entry>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 <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> fragment or the <varname>CacheDirectory=</varname> directive of service units (see <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>) may be used.</entry>
</row>
<row>
<entry><filename>/var/lib/<replaceable>package</replaceable>/</filename></entry>
<entry>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 <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> fragment or the <varname>StateDirectory=</varname> directive of service units (see <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>) may be used.</entry>
</row>
<row>
<entry><filename>/var/log/<replaceable>package</replaceable>/</filename></entry>
<entry>Persistent log data of the package. As above, the package should make sure to create this directory if necessary, possibly using <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> or <varname>LogsDirectory=</varname> (see <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>), as it might be missing.</entry>
</row>
<row>
<entry><filename>/var/spool/<replaceable>package</replaceable>/</filename></entry>
<entry>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.</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1>
<title>User Packages</title>
<para>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.)</para>
<table>
<title>Vendor package file locations under the home directory of the user</title>
<tgroup cols='2' align='left' colsep='1' rowsep='1'>
<colspec colname="directory" />
<colspec colname="purpose" />
<thead>
<row>
<entry>Directory</entry>
<entry>Purpose</entry>
</row>
</thead>
<tbody>
<row>
<entry><filename>~/.local/bin/</filename></entry>
<entry>Package executables that shall appear in the <varname>$PATH</varname> 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.</entry>
</row>
<row>
<entry><filename>~/.local/lib/<replaceable>arch-id</replaceable>/</filename></entry>
<entry>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.</entry>
</row>
<row>
<entry><filename>~/.local/lib/<replaceable>package</replaceable>/</filename></entry>
<entry>Private, static vendor resources of the package, compatible with any architecture, or any other kind of read-only vendor data.</entry>
</row>
<row>
<entry><filename>~/.local/lib/<replaceable>arch-id</replaceable>/<replaceable>package</replaceable>/</filename></entry>
<entry>Private other vendor resources of the package that are architecture-specific and cannot be shared between architectures.</entry>
</row>
</tbody>
</tgroup>
</table>
<para>Additional static vendor files may be installed in the <filename>~/.local/share/</filename>
hierarchy, mirroring the subdirectories specified in the section "Vendor-supplied operating system
resources" above.</para>
<para>The following directories shall be used by the package for per-user local configuration and files
created during runtime:</para>
<table>
<title>User package variable file locations</title>
<tgroup cols='2' align='left' colsep='1' rowsep='1'>
<colspec colname="directory" />
<colspec colname="purpose" />
<thead>
<row>
<entry>Directory</entry>
<entry>Purpose</entry>
</row>
</thead>
<tbody>
<row>
<entry><filename>~/.config/<replaceable>package</replaceable>/</filename></entry>
<entry>User-specific configuration and state for the package. It is required to default to safe fallbacks if this configuration is missing.</entry>
</row>
<row>
<entry><filename><varname>$XDG_RUNTIME_DIR</varname>/<replaceable>package</replaceable>/</filename></entry>
<entry>User runtime data for the package.</entry>
</row>
<row>
<entry><filename>~/.cache/<replaceable>package</replaceable>/</filename></entry>
<entry>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.</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1>
<title>See Also</title>
<para><simplelist type="inline">
<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
<member><citerefentry project='man-pages'><refentrytitle>hier</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>systemd-path</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
<member><citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
</simplelist></para>
</refsect1>
</refentry>