systemd/man/file-hierarchy.xml

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<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. 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 <filename>/usr/include/</filename> or
    <filename>/var/spool/</filename> 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.</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></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></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></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></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></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></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></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></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></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></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></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></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></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></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.</para>

        <para>To query <varname>$libdir</varname> for the primary architecture of the system, invoke:
        <programlisting>systemd-path system-library-arch</programlisting></para></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>

        <para>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
        <filename>/usr/lib/</filename>, where ownership is generally not shared.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><filename>/usr/share/doc/</filename></term>
        <listitem><para>Documentation for the operating system or system packages.</para></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></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></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></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></listitem>
      </varlistentry>

      <varlistentry>
        <term><filename>/var/lib/</filename></term>
        <listitem><para>Persistent system data. System components may place private data in this
        directory.</para></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></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></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></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></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></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></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></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></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></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></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></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></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></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></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></listitem>
      </varlistentry>

      <varlistentry>
        <term><filename>~/.local/lib/</filename></term>

        <listitem><para>Static, private vendor data that is compatible with all
        architectures.</para></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></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></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></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>

    <para>Applications should expect that a security policy might be enforced on a system that enforces these
    rules.</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>
        </tbody>
      </tgroup>
    </table>

    <para>Additional static vendor files with shared ownership 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>
        </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 with shared ownership 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 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>
          <row>
      <entry><filename>~/.local/state/<replaceable>package</replaceable>/</filename></entry>
      <entry>Persistent state data of the package.</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>