Adding upstream version 241.upstream/241upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1866 insertions, 0 deletions

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+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
+<!ENTITY % entities SYSTEM "custom-entities.ent" >
+%entities;
+]>
+
+<!--
+  SPDX-License-Identifier: LGPL-2.1+
+-->
+
+<refentry id="systemd.unit">
+
+  <refentryinfo>
+    <title>systemd.unit</title>
+    <productname>systemd</productname>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>systemd.unit</refentrytitle>
+    <manvolnum>5</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>systemd.unit</refname>
+    <refpurpose>Unit configuration</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <para><filename><replaceable>service</replaceable>.service</filename>,
+    <filename><replaceable>socket</replaceable>.socket</filename>,
+    <filename><replaceable>device</replaceable>.device</filename>,
+    <filename><replaceable>mount</replaceable>.mount</filename>,
+    <filename><replaceable>automount</replaceable>.automount</filename>,
+    <filename><replaceable>swap</replaceable>.swap</filename>,
+    <filename><replaceable>target</replaceable>.target</filename>,
+    <filename><replaceable>path</replaceable>.path</filename>,
+    <filename><replaceable>timer</replaceable>.timer</filename>,
+    <filename><replaceable>slice</replaceable>.slice</filename>,
+    <filename><replaceable>scope</replaceable>.scope</filename></para>
+
+    <refsect2>
+      <title>System Unit Search Path</title>
+
+      <para><literallayout><filename>/etc/systemd/system.control/*</filename>
+<filename>/run/systemd/system.control/*</filename>
+<filename>/run/systemd/transient/*</filename>
+<filename>/run/systemd/generator.early/*</filename>
+<filename>/etc/systemd/system/*</filename>
+<filename>/etc/systemd/systemd.attached/*</filename>
+<filename>/run/systemd/system/*</filename>
+<filename>/run/systemd/systemd.attached/*</filename>
+<filename>/run/systemd/generator/*</filename>
+<filename>…</filename>
+<filename>/usr/lib/systemd/system/*</filename>
+<filename>/run/systemd/generator.late/*</filename></literallayout></para>
+    </refsect2>
+
+    <refsect2>
+      <title>User Unit Search Path</title>
+      <para><literallayout><filename>~/.config/systemd/user.control/*</filename>
+<filename>$XDG_RUNTIME_DIR/systemd/user.control/*</filename>
+<filename>$XDG_RUNTIME_DIR/systemd/transient/*</filename>
+<filename>$XDG_RUNTIME_DIR/systemd/generator.early/*</filename>
+<filename>~/.config/systemd/user/*</filename>
+<filename>/etc/systemd/user/*</filename>
+<filename>$XDG_RUNTIME_DIR/systemd/user/*</filename>
+<filename>/run/systemd/user/*</filename>
+<filename>$XDG_RUNTIME_DIR/systemd/generator/*</filename>
+<filename>~/.local/share/systemd/user/*</filename>
+<filename>…</filename>
+<filename>/usr/lib/systemd/user/*</filename>
+<filename>$XDG_RUNTIME_DIR/systemd/generator.late/*</filename></literallayout></para>
+    </refsect2>
+
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para>A unit file is a plain text ini-style file that encodes information about a service, a
+    socket, a device, a mount point, an automount point, a swap file or partition, a start-up
+    target, a watched file system path, a timer controlled and supervised by
+    <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, a
+    resource management slice or a group of externally created processes. See
+    <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for a general description of the syntax.</para>
+
+    <para>This man page lists the common configuration options of all
+    the unit types. These options need to be configured in the [Unit]
+    or [Install] sections of the unit files.</para>
+
+    <para>In addition to the generic [Unit] and [Install] sections
+    described here, each unit may have a type-specific section, e.g.
+    [Service] for a service unit. See the respective man pages for
+    more information:
+    <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+    </para>
+
+    <para>Unit files are loaded from a set of paths determined during
+    compilation, described in the next section.</para>
+
+    <para>Unit files can be parameterized by a single argument called the "instance name". The unit
+    is then constructed based on a "template file" which serves as the definition of multiple
+    services or other units. A template unit must have a single <literal>@</literal> at the end of
+    the name (right before the type suffix). The name of the full unit is formed by inserting the
+    instance name between <literal>@</literal> and the unit type suffix. In the unit file itself,
+    the instance parameter may be referred to using <literal>%i</literal> and other specifiers, see
+    below.</para>
+
+    <para>Unit files may contain additional options on top of those
+    listed here. If systemd encounters an unknown option, it will
+    write a warning log message but continue loading the unit. If an
+    option or section name is prefixed with <option>X-</option>, it is
+    ignored completely by systemd. Options within an ignored section
+    do not need the prefix. Applications may use this to include
+    additional information in the unit files.</para>
+
+    <para>Units can be aliased (have an alternative name), by creating a symlink from the new name
+    to the existing name in one of the unit search paths. For example,
+    <filename>systemd-networkd.service</filename> has the alias
+    <filename>dbus-org.freedesktop.network1.service</filename>, created during installation as the
+    symlink <filename>/usr/lib/systemd/system/dbus-org.freedesktop.network1.service</filename>. In
+    addition, unit files may specify aliases through the <varname>Alias=</varname> directive in the
+    [Install] section; those aliases are only effective when the unit is enabled. When the unit is
+    enabled, symlinks will be created for those names, and removed when the unit is disabled. For
+    example, <filename>reboot.target</filename> specifies
+    <varname>Alias=ctrl-alt-del.target</varname>, so when enabled it will be invoked whenever
+    CTRL+ALT+DEL is pressed. Alias names may be used in commands like <command>enable</command>,
+    <command>disable</command>, <command>start</command>, <command>stop</command>,
+    <command>status</command>, …, and in unit dependency directives <varname>Wants=</varname>,
+    <varname>Requires=</varname>, <varname>Before=</varname>, <varname>After=</varname>, …, with the
+    limitation that aliases specified through <varname>Alias=</varname> are only effective when the
+    unit is enabled. Aliases cannot be used with the <command>preset</command> command.</para>
+
+    <para>Along with a unit file <filename>foo.service</filename>, the directory
+    <filename>foo.service.wants/</filename> may exist. All unit files symlinked from such a
+    directory are implicitly added as dependencies of type <varname>Wants=</varname> to the unit.
+    This is useful to hook units into the start-up of other units, without having to modify their
+    unit files. For details about the semantics of <varname>Wants=</varname>, see below. The
+    preferred way to create symlinks in the <filename>.wants/</filename> directory of a unit file is
+    with the <command>enable</command> command of the
+    <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+    tool which reads information from the [Install] section of unit files (see below). A similar
+    functionality exists for <varname>Requires=</varname> type dependencies as well, the directory
+    suffix is <filename>.requires/</filename> in this case.</para>
+
+    <para>Along with a unit file <filename>foo.service</filename>, a "drop-in" directory
+    <filename>foo.service.d/</filename> may exist. All files with the suffix <literal>.conf</literal> from this
+    directory will be parsed after the unit file itself is parsed. This is useful to alter or add configuration
+    settings for a unit, without having to modify unit files. Drop-in files must contain appropriate section
+    headers. For instantiated units, this logic will first look for the instance <literal>.d/</literal> subdirectory
+    (e.g. <literal>foo@bar.service.d/</literal>) and read its <literal>.conf</literal> files, followed by the template
+    <literal>.d/</literal> subdirectory (e.g. <literal>foo@.service.d/</literal>) and the <literal>.conf</literal>
+    files there. Moreover for units names containing dashes (<literal>-</literal>), the set of directories generated by
+    truncating the unit name after all dashes is searched too. Specifically, for a unit name
+    <filename>foo-bar-baz.service</filename> not only the regular drop-in directory
+    <filename>foo-bar-baz.service.d/</filename> is searched but also both <filename>foo-bar-.service.d/</filename> and
+    <filename>foo-.service.d/</filename>. This is useful for defining common drop-ins for a set of related units, whose
+    names begin with a common prefix. This scheme is particularly useful for mount, automount and slice units, whose
+    systematic naming structure is built around dashes as component separators. Note that equally named drop-in files
+    further down the prefix hierarchy override those further up,
+    i.e. <filename>foo-bar-.service.d/10-override.conf</filename> overrides
+    <filename>foo-.service.d/10-override.conf</filename>.</para>
+
+    <para>In addition to <filename>/etc/systemd/system</filename>, the drop-in <literal>.d/</literal>
+    directories for system services can be placed in <filename>/usr/lib/systemd/system</filename> or
+    <filename>/run/systemd/system</filename> directories. Drop-in files in <filename>/etc</filename>
+    take precedence over those in <filename>/run</filename> which in turn take precedence over those
+    in <filename>/usr/lib</filename>. Drop-in files under any of these directories take precedence
+    over unit files wherever located. Multiple drop-in files with different names are applied in
+    lexicographic order, regardless of which of the directories they reside in.</para>
+
+    <!-- Note that we do not document .include here, as we consider it mostly obsolete, and want
+         people to use .d/ drop-ins instead. -->
+
+    <para>Note that while systemd offers a flexible dependency system
+    between units it is recommended to use this functionality only
+    sparingly and instead rely on techniques such as bus-based or
+    socket-based activation which make dependencies implicit,
+    resulting in a both simpler and more flexible system.</para>
+
+    <para>As mentioned above, a unit may be instantiated from a template file. This allows creation
+    of multiple units from a single configuration file. If systemd looks for a unit configuration
+    file, it will first search for the literal unit name in the file system. If that yields no
+    success and the unit name contains an <literal>@</literal> character, systemd will look for a
+    unit template that shares the same name but with the instance string (i.e. the part between the
+    <literal>@</literal> character and the suffix) removed. Example: if a service
+    <filename>getty@tty3.service</filename> is requested and no file by that name is found, systemd
+    will look for <filename>getty@.service</filename> and instantiate a service from that
+    configuration file if it is found.</para>
+
+    <para>To refer to the instance string from within the
+    configuration file you may use the special <literal>%i</literal>
+    specifier in many of the configuration options. See below for
+    details.</para>
+
+    <para>If a unit file is empty (i.e. has the file size 0) or is
+    symlinked to <filename>/dev/null</filename>, its configuration
+    will not be loaded and it appears with a load state of
+    <literal>masked</literal>, and cannot be activated. Use this as an
+    effective way to fully disable a unit, making it impossible to
+    start it even manually.</para>
+
+    <para>The unit file format is covered by the
+    <ulink
+    url="https://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
+    Stability Promise</ulink>.</para>
+
+  </refsect1>
+
+  <refsect1>
+    <title>String Escaping for Inclusion in Unit Names</title>
+
+    <para>Sometimes it is useful to convert arbitrary strings into unit names. To facilitate this, a method of string
+    escaping is used, in order to map strings containing arbitrary byte values (except NUL) into valid unit names and
+    their restricted character set. A common special case are unit names that reflect paths to objects in the file
+    system hierarchy. Example: a device unit <filename>dev-sda.device</filename> refers to a device with the device
+    node <filename noindex='true'>/dev/sda</filename> in the file system.</para>
+
+    <para>The escaping algorithm operates as follows: given a string, any <literal>/</literal> character is replaced by
+    <literal>-</literal>, and all other characters which are not ASCII alphanumerics or <literal>_</literal> are
+    replaced by C-style <literal>\x2d</literal> escapes. In addition, <literal>.</literal> is replaced with such a
+    C-style escape when it would appear as the first character in the escaped string.</para>
+
+    <para>When the input qualifies as absolute file system path, this algorithm is extended slightly: the path to the
+    root directory <literal>/</literal> is encoded as single dash <literal>-</literal>. In addition, any leading,
+    trailing or duplicate <literal>/</literal> characters are removed from the string before transformation. Example:
+    <filename>/foo//bar/baz/</filename> becomes <literal>foo-bar-baz</literal>.</para>
+
+    <para>This escaping is fully reversible, as long as it is known whether the escaped string was a path (the
+    unescaping results are different for paths and non-path strings). The
+    <citerefentry><refentrytitle>systemd-escape</refentrytitle><manvolnum>1</manvolnum></citerefentry> command may be
+    used to apply and reverse escaping on arbitrary strings. Use <command>systemd-escape --path</command> to escape
+    path strings, and <command>systemd-escape</command> without <option>--path</option> otherwise.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Automatic dependencies</title>
+
+    <refsect2>
+      <title>Implicit Dependencies</title>
+
+      <para>A number of unit dependencies are implicitly established, depending on unit type and
+      unit configuration. These implicit dependencies can make unit configuration file cleaner. For
+      the implicit dependencies in each unit type, please refer to section "Implicit Dependencies"
+      in respective man pages.</para>
+
+      <para>For example, service units with <varname>Type=dbus</varname> automatically acquire
+      dependencies of type <varname>Requires=</varname> and <varname>After=</varname> on
+      <filename>dbus.socket</filename>. See
+      <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+      for details.</para>
+    </refsect2>
+
+    <refsect2>
+      <title>Default Dependencies</title>
+
+      <para>Default dependencies are similar to implicit dependencies, but can be turned on and off
+      by setting <varname>DefaultDependencies=</varname> to <varname>yes</varname> (the default) and
+      <varname>no</varname>, while implicit dependencies are always in effect. See section "Default
+      Dependencies" in respective man pages for the effect of enabling
+      <varname>DefaultDependencies=</varname> in each unit types.</para>
+
+      <para>For example, target units will complement all configured dependencies of type
+      <varname>Wants=</varname> or <varname>Requires=</varname> with dependencies of type
+      <varname>After=</varname> unless <varname>DefaultDependencies=no</varname> is set in the
+      specified units. See
+      <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+      for details. Note that this behavior can be turned off by setting
+      <varname>DefaultDependencies=no</varname>.</para>
+    </refsect2>
+  </refsect1>
+
+  <refsect1>
+    <title>Unit File Load Path</title>
+
+    <para>Unit files are loaded from a set of paths determined during
+    compilation, described in the two tables below. Unit files found
+    in directories listed earlier override files with the same name in
+    directories lower in the list.</para>
+
+    <para>When the variable <varname>$SYSTEMD_UNIT_PATH</varname> is set,
+    the contents of this variable overrides the unit load path. If
+    <varname>$SYSTEMD_UNIT_PATH</varname> ends with an empty component
+    (<literal>:</literal>), the usual unit load path will be appended
+    to the contents of the variable.</para>
+
+    <table>
+      <title>
+        Load path when running in system mode (<option>--system</option>).
+      </title>
+
+      <tgroup cols='2'>
+        <colspec colname='path' />
+        <colspec colname='expl' />
+        <thead>
+          <row>
+            <entry>Path</entry>
+            <entry>Description</entry>
+          </row>
+        </thead>
+        <tbody>
+          <row>
+            <entry><filename>/etc/systemd/system.control</filename></entry>
+            <entry morerows="1">Persistent and transient configuration created using the dbus API</entry>
+          </row>
+          <row>
+            <entry><filename>/run/systemd/system.control</filename></entry>
+          </row>
+          <row>
+            <entry><filename>/run/systemd/transient</filename></entry>
+            <entry>Dynamic configuration for transient units</entry>
+          </row>
+          <row>
+            <entry><filename>/run/systemd/generator.early</filename></entry>
+            <entry>Generated units with high priority (see <replaceable>early-dir</replaceable> in <citerefentry
+            ><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>)</entry>
+          </row>
+          <row>
+            <entry><filename>/etc/systemd/system</filename></entry>
+            <entry>Local configuration</entry>
+          </row>
+          <row>
+            <entry><filename>/run/systemd/system</filename></entry>
+            <entry>Runtime units</entry>
+          </row>
+          <row>
+            <entry><filename>/run/systemd/generator</filename></entry>
+            <entry>Generated units with medium priority (see <replaceable>normal-dir</replaceable> in <citerefentry
+            ><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>)</entry>
+          </row>
+          <row>
+            <entry><filename>/usr/local/lib/systemd/system</filename></entry>
+            <entry morerows="1">Units of installed packages</entry>
+          </row>
+          <row>
+            <entry><filename>/usr/lib/systemd/system</filename></entry>
+          </row>
+          <row>
+            <entry><filename>/run/systemd/generator.late</filename></entry>
+            <entry>Generated units with low priority (see <replaceable>late-dir</replaceable> in <citerefentry
+            ><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>)</entry>
+          </row>
+        </tbody>
+      </tgroup>
+    </table>
+
+    <table>
+      <title>
+        Load path when running in user mode (<option>--user</option>).
+      </title>
+
+      <tgroup cols='2'>
+        <colspec colname='path' />
+        <colspec colname='expl' />
+        <thead>
+          <row>
+            <entry>Path</entry>
+            <entry>Description</entry>
+          </row>
+        </thead>
+        <tbody>
+          <row>
+            <entry><filename>$XDG_CONFIG_HOME/systemd/user.control</filename> or <filename
+            >~/.config/systemd/user.control</filename></entry>
+            <entry morerows="1">Persistent and transient configuration created using the dbus API (<varname>$XDG_CONFIG_HOME</varname> is used if set, <filename>~/.config</filename> otherwise)</entry>
+          </row>
+          <row>
+            <entry><filename>$XDG_RUNTIME_DIR/systemd/user.control</filename></entry>
+          </row>
+          <row>
+            <entry><filename>/run/systemd/transient</filename></entry>
+            <entry>Dynamic configuration for transient units</entry>
+          </row>
+          <row>
+            <entry><filename>/run/systemd/generator.early</filename></entry>
+            <entry>Generated units with high priority (see <replaceable>early-dir</replaceable> in <citerefentry
+            ><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>)</entry>
+          </row>
+          <row>
+            <entry><filename>$XDG_CONFIG_HOME/systemd/user</filename> or <filename>$HOME/.config/systemd/user</filename></entry>
+            <entry>User configuration (<varname>$XDG_CONFIG_HOME</varname> is used if set, <filename>~/.config</filename> otherwise)</entry>
+          </row>
+          <row>
+            <entry><filename>/etc/systemd/user</filename></entry>
+            <entry>Local configuration</entry>
+          </row>
+          <row>
+            <entry><filename>$XDG_RUNTIME_DIR/systemd/user</filename></entry>
+            <entry>Runtime units (only used when $XDG_RUNTIME_DIR is set)</entry>
+          </row>
+          <row>
+            <entry><filename>/run/systemd/user</filename></entry>
+            <entry>Runtime units</entry>
+          </row>
+          <row>
+            <entry><filename>$XDG_RUNTIME_DIR/systemd/generator</filename></entry>
+            <entry>Generated units with medium priority (see <replaceable>normal-dir</replaceable> in <citerefentry
+            ><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>)</entry>
+          </row>
+          <row>
+            <entry><filename>$XDG_DATA_HOME/systemd/user</filename> or <filename>$HOME/.local/share/systemd/user</filename></entry>
+            <entry>Units of packages that have been installed in the home directory (<varname>$XDG_DATA_HOME</varname> is used if set, <filename>~/.local/share</filename> otherwise)</entry>
+          </row>
+          <row>
+            <entry><filename>$dir/systemd/user</filename> for each <varname noindex='true'>$dir</varname> in <varname>$XDG_DATA_DIRS</varname></entry>
+            <entry>Additional locations for installed user units, one for each entry in <varname>$XDG_DATA_DIRS</varname></entry>
+          </row>
+          <row>
+            <entry><filename>/usr/local/lib/systemd/user</filename></entry>
+            <entry morerows="1">Units of packages that have been installed system-wide</entry>
+          </row>
+          <row>
+            <entry><filename>/usr/lib/systemd/user</filename></entry>
+          </row>
+          <row>
+            <entry><filename>$XDG_RUNTIME_DIR/systemd/generator.late</filename></entry>
+            <entry>Generated units with low priority (see <replaceable>late-dir</replaceable> in <citerefentry
+            ><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>)</entry>
+          </row>
+        </tbody>
+      </tgroup>
+    </table>
+
+    <para>The set of load paths for the user manager instance may be augmented or
+    changed using various environment variables. And environment variables may in
+    turn be set using environment generators, see
+    <citerefentry><refentrytitle>systemd.environment-generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
+    In particular, <varname>$XDG_DATA_HOME</varname> and
+    <varname>$XDG_DATA_DIRS</varname> may be easily set using
+    <citerefentry><refentrytitle>systemd-environment-d-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
+    Thus, directories listed here are just the defaults. To see the actual list that
+    would be used based on compilation options and current environment use
+    <programlisting>systemd-analyze --user unit-paths</programlisting>
+    </para>
+
+    <para>Moreover, additional units might be loaded into systemd ("linked") from
+    directories not on the unit load path. See the <command>link</command> command
+    for
+    <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
+    </para>
+  </refsect1>
+
+  <refsect1>
+    <title>Unit Garbage Collection</title>
+
+    <para>The system and service manager loads a unit's configuration automatically when a unit is referenced for the
+    first time. It will automatically unload the unit configuration and state again when the unit is not needed anymore
+    ("garbage collection"). A unit may be referenced through a number of different mechanisms:</para>
+
+    <orderedlist>
+      <listitem><para>Another loaded unit references it with a dependency such as <varname>After=</varname>,
+      <varname>Wants=</varname>, …</para></listitem>
+
+      <listitem><para>The unit is currently starting, running, reloading or stopping.</para></listitem>
+
+      <listitem><para>The unit is currently in the <constant>failed</constant> state. (But see below.)</para></listitem>
+
+      <listitem><para>A job for the unit is pending.</para></listitem>
+
+      <listitem><para>The unit is pinned by an active IPC client program.</para></listitem>
+
+      <listitem><para>The unit is a special "perpetual" unit that is always active and loaded. Examples for perpetual
+      units are the root mount unit <filename>-.mount</filename> or the scope unit <filename>init.scope</filename> that
+      the service manager itself lives in.</para></listitem>
+
+      <listitem><para>The unit has running processes associated with it.</para></listitem>
+    </orderedlist>
+
+    <para>The garbage collection logic may be altered with the <varname>CollectMode=</varname> option, which allows
+    configuration whether automatic unloading of units that are in <constant>failed</constant> state is permissible,
+    see below.</para>
+
+    <para>Note that when a unit's configuration and state is unloaded, all execution results, such as exit codes, exit
+    signals, resource consumption and other statistics are lost, except for what is stored in the log subsystem.</para>
+
+    <para>Use <command>systemctl daemon-reload</command> or an equivalent command to reload unit configuration while
+    the unit is already loaded. In this case all configuration settings are flushed out and replaced with the new
+    configuration (which however might not be in effect immediately), however all runtime state is
+    saved/restored.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>[Unit] Section Options</title>
+
+    <para>The unit file may include a [Unit] section, which carries
+    generic information about the unit that is not dependent on the
+    type of unit:</para>
+
+    <variablelist class='unit-directives'>
+
+      <varlistentry>
+        <term><varname>Description=</varname></term>
+        <listitem><para>A human readable name for the unit. This is used by
+        <command>systemd</command> (and other UIs) as the label for the unit, so this string should
+        identify the unit rather than describe it, despite the name. <literal>Apache2 Web
+        Server</literal> is a good example. Bad examples are <literal>high-performance light-weight
+        HTTP server</literal> (too generic) or <literal>Apache2</literal> (too specific and
+        meaningless for people who do not know Apache). <command>systemd</command> will use this
+        string as a noun in status messages (<literal>Starting
+        <replaceable>description</replaceable>...</literal>, <literal>Started
+        <replaceable>description</replaceable>.</literal>, <literal>Reached target
+        <replaceable>description</replaceable>.</literal>, <literal>Failed to start
+        <replaceable>description</replaceable>.</literal>), so it should be capitalized, and should
+        not be a full sentence or a phrase with a continous verb. Bad examples include
+        <literal>exiting the container</literal> or <literal>updating the database once per
+        day.</literal>.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>Documentation=</varname></term>
+        <listitem><para>A space-separated list of URIs referencing
+        documentation for this unit or its configuration. Accepted are
+        only URIs of the types <literal>http://</literal>,
+        <literal>https://</literal>, <literal>file:</literal>,
+        <literal>info:</literal>, <literal>man:</literal>. For more
+        information about the syntax of these URIs, see <citerefentry
+        project='man-pages'><refentrytitle>uri</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
+        The URIs should be listed in order of relevance, starting with
+        the most relevant. It is a good idea to first reference
+        documentation that explains what the unit's purpose is,
+        followed by how it is configured, followed by any other
+        related documentation. This option may be specified more than
+        once, in which case the specified list of URIs is merged. If
+        the empty string is assigned to this option, the list is reset
+        and all prior assignments will have no
+        effect.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>Requires=</varname></term>
+
+        <listitem><para>Configures requirement dependencies on other units. If this unit gets activated, the units
+        listed here will be activated as well. If one of the other units fails to activate, and an ordering dependency
+        <varname>After=</varname> on the failing unit is set, this unit will not be started. Besides, with or without
+        specifying <varname>After=</varname>, this unit will be stopped if one of the other units is explicitly
+        stopped. This option may be specified more than once or multiple space-separated units may be
+        specified in one option in which case requirement dependencies for all listed names will be created. Note that
+        requirement dependencies do not influence the order in which services are started or stopped.  This has to be
+        configured independently with the <varname>After=</varname> or <varname>Before=</varname> options. If a unit
+        <filename>foo.service</filename> requires a unit <filename>bar.service</filename> as configured with
+        <varname>Requires=</varname> and no ordering is configured with <varname>After=</varname> or
+        <varname>Before=</varname>, then both units will be started simultaneously and without any delay between them
+        if <filename>foo.service</filename> is activated. Often, it is a better choice to use <varname>Wants=</varname>
+        instead of <varname>Requires=</varname> in order to achieve a system that is more robust when dealing with
+        failing services.</para>
+
+        <para>Note that this dependency type does not imply that the other unit always has to be in active state when
+        this unit is running. Specifically: failing condition checks (such as <varname>ConditionPathExists=</varname>,
+        <varname>ConditionPathIsSymbolicLink=</varname>, … — see below) do not cause the start job of a unit with a
+        <varname>Requires=</varname> dependency on it to fail. Also, some unit types may deactivate on their own (for
+        example, a service process may decide to exit cleanly, or a device may be unplugged by the user), which is not
+        propagated to units having a <varname>Requires=</varname> dependency. Use the <varname>BindsTo=</varname>
+        dependency type together with <varname>After=</varname> to ensure that a unit may never be in active state
+        without a specific other unit also in active state (see below).</para>
+
+        <para>Note that dependencies of this type may also be configured outside of the unit configuration file by
+        adding a symlink to a <filename>.requires/</filename> directory accompanying the unit file. For details, see
+        above.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>Requisite=</varname></term>
+
+        <listitem><para>Similar to <varname>Requires=</varname>. However, if the units listed here
+        are not started already, they will not be started and the starting of this unit will fail
+        immediately. <varname>Requisite=</varname> does not imply an ordering dependency, even if
+        both units are started in the same transaction. Hence this setting should usually be
+        combined with <varname>After=</varname>, to ensure this unit is not started before the other
+        unit.</para>
+
+        <para>When <varname>Requisite=b.service</varname> is used on
+        <filename>a.service</filename>, this dependency will show as
+        <varname>RequisiteOf=a.service</varname> in property listing of
+        <filename>b.service</filename>. <varname>RequisiteOf=</varname>
+        dependency cannot be specified directly.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>Wants=</varname></term>
+
+        <listitem><para>A weaker version of
+        <varname>Requires=</varname>. Units listed in this option will
+        be started if the configuring unit is. However, if the listed
+        units fail to start or cannot be added to the transaction,
+        this has no impact on the validity of the transaction as a
+        whole. This is the recommended way to hook start-up of one
+        unit to the start-up of another unit.</para>
+
+        <para>Note that dependencies of this type may also be
+        configured outside of the unit configuration file by adding
+        symlinks to a <filename>.wants/</filename> directory
+        accompanying the unit file. For details, see
+        above.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>BindsTo=</varname></term>
+
+        <listitem><para>Configures requirement dependencies, very similar in style to
+        <varname>Requires=</varname>. However, this dependency type is stronger: in addition to the effect of
+        <varname>Requires=</varname> it declares that if the unit bound to is stopped, this unit will be stopped
+        too. This means a unit bound to another unit that suddenly enters inactive state will be stopped too.
+        Units can suddenly, unexpectedly enter inactive state for different reasons: the main process of a service unit
+        might terminate on its own choice, the backing device of a device unit might be unplugged or the mount point of
+        a mount unit might be unmounted without involvement of the system and service manager.</para>
+
+        <para>When used in conjunction with <varname>After=</varname> on the same unit the behaviour of
+        <varname>BindsTo=</varname> is even stronger. In this case, the unit bound to strictly has to be in active
+        state for this unit to also be in active state. This not only means a unit bound to another unit that suddenly
+        enters inactive state, but also one that is bound to another unit that gets skipped due to a failed condition
+        check (such as <varname>ConditionPathExists=</varname>, <varname>ConditionPathIsSymbolicLink=</varname>, … —
+        see below) will be stopped, should it be running. Hence, in many cases it is best to combine
+        <varname>BindsTo=</varname> with <varname>After=</varname>.</para>
+
+        <para>When <varname>BindsTo=b.service</varname> is used on
+        <filename>a.service</filename>, this dependency will show as
+        <varname>BoundBy=a.service</varname> in property listing of
+        <filename>b.service</filename>. <varname>BoundBy=</varname>
+        dependency cannot be specified directly.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>PartOf=</varname></term>
+
+        <listitem><para>Configures dependencies similar to
+        <varname>Requires=</varname>, but limited to stopping and
+        restarting of units. When systemd stops or restarts the units
+        listed here, the action is propagated to this unit. Note that
+        this is a one-way dependency — changes to this unit do not
+        affect the listed units.</para>
+
+        <para>When <varname>PartOf=b.service</varname> is used on
+        <filename>a.service</filename>, this dependency will show as
+        <varname>ConsistsOf=a.service</varname> in property listing of
+        <filename>b.service</filename>. <varname>ConsistsOf=</varname>
+        dependency cannot be specified directly.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>Conflicts=</varname></term>
+
+        <listitem><para>A space-separated list of unit names.
+        Configures negative requirement dependencies. If a unit has a
+        <varname>Conflicts=</varname> setting on another unit,
+        starting the former will stop the latter and vice versa. Note
+        that this setting is independent of and orthogonal to the
+        <varname>After=</varname> and <varname>Before=</varname>
+        ordering dependencies.</para>
+
+        <para>If a unit A that conflicts with a unit B is scheduled to
+        be started at the same time as B, the transaction will either
+        fail (in case both are required parts of the transaction) or be
+        modified to be fixed (in case one or both jobs are not a
+        required part of the transaction). In the latter case, the job
+        that is not required will be removed, or in case both are
+        not required, the unit that conflicts will be started and the
+        unit that is conflicted is stopped.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>Before=</varname></term>
+        <term><varname>After=</varname></term>
+
+        <listitem><para>These two settings expect a space-separated list of unit names. They configure ordering
+        dependencies between units. If a unit <filename>foo.service</filename> contains a setting
+        <option>Before=bar.service</option> and both units are being started, <filename>bar.service</filename>'s
+        start-up is delayed until <filename>foo.service</filename> has finished starting up.  Note that this setting is
+        independent of and orthogonal to the requirement dependencies as configured by <varname>Requires=</varname>,
+        <varname>Wants=</varname> or <varname>BindsTo=</varname>. It is a common pattern to include a unit name in both
+        the <varname>After=</varname> and <varname>Requires=</varname> options, in which case the unit listed will be
+        started before the unit that is configured with these options. This option may be specified more than once, in
+        which case ordering dependencies for all listed names are created. <varname>After=</varname> is the inverse of
+        <varname>Before=</varname>, i.e. while <varname>After=</varname> ensures that the configured unit is started
+        after the listed unit finished starting up, <varname>Before=</varname> ensures the opposite, that the
+        configured unit is fully started up before the listed unit is started. Note that when two units with an
+        ordering dependency between them are shut down, the inverse of the start-up order is applied. i.e. if a unit is
+        configured with <varname>After=</varname> on another unit, the former is stopped before the latter if both are
+        shut down. Given two units with any ordering dependency between them, if one unit is shut down and the other is
+        started up, the shutdown is ordered before the start-up. It doesn't matter if the ordering dependency is
+        <varname>After=</varname> or <varname>Before=</varname>, in this case. It also doesn't matter which of the two
+        is shut down, as long as one is shut down and the other is started up. The shutdown is ordered before the
+        start-up in all cases. If two units have no ordering dependencies between them, they are shut down or started
+        up simultaneously, and no ordering takes place. It depends on the unit type when precisely a unit has finished
+        starting up. Most importantly, for service units start-up is considered completed for the purpose of
+        <varname>Before=</varname>/<varname>After=</varname> when all its configured start-up commands have been
+        invoked and they either failed or reported start-up success.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>OnFailure=</varname></term>
+
+        <listitem><para>A space-separated list of one or more units
+        that are activated when this unit enters the
+        <literal>failed</literal> state.  A service unit using
+        <varname>Restart=</varname> enters the failed state only after
+        the start limits are reached.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>PropagatesReloadTo=</varname></term>
+        <term><varname>ReloadPropagatedFrom=</varname></term>
+
+        <listitem><para>A space-separated list of one or more units
+        where reload requests on this unit will be propagated to, or
+        reload requests on the other unit will be propagated to this
+        unit, respectively. Issuing a reload request on a unit will
+        automatically also enqueue a reload request on all units that
+        the reload request shall be propagated to via these two
+        settings.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>JoinsNamespaceOf=</varname></term>
+
+        <listitem><para>For units that start processes (such as
+        service units), lists one or more other units whose network
+        and/or temporary file namespace to join. This only applies to
+        unit types which support the
+        <varname>PrivateNetwork=</varname> and
+        <varname>PrivateTmp=</varname> directives (see
+        <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        for details). If a unit that has this setting set is started,
+        its processes will see the same <filename>/tmp</filename>,
+        <filename>/var/tmp</filename> and network namespace as one
+        listed unit that is started. If multiple listed units are
+        already started, it is not defined which namespace is joined.
+        Note that this setting only has an effect if
+        <varname>PrivateNetwork=</varname> and/or
+        <varname>PrivateTmp=</varname> is enabled for both the unit
+        that joins the namespace and the unit whose namespace is
+        joined.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>RequiresMountsFor=</varname></term>
+
+        <listitem><para>Takes a space-separated list of absolute
+        paths. Automatically adds dependencies of type
+        <varname>Requires=</varname> and <varname>After=</varname> for
+        all mount units required to access the specified path.</para>
+
+        <para>Mount points marked with <option>noauto</option> are not
+        mounted automatically through <filename>local-fs.target</filename>,
+        but are still honored for the purposes of this option, i.e. they
+        will be pulled in by this unit.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>OnFailureJobMode=</varname></term>
+
+        <listitem><para>Takes a value of
+        <literal>fail</literal>,
+        <literal>replace</literal>,
+        <literal>replace-irreversibly</literal>,
+        <literal>isolate</literal>,
+        <literal>flush</literal>,
+        <literal>ignore-dependencies</literal> or
+        <literal>ignore-requirements</literal>. Defaults to
+        <literal>replace</literal>. Specifies how the units listed in
+        <varname>OnFailure=</varname> will be enqueued. See
+        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
+        <option>--job-mode=</option> option for details on the
+        possible values. If this is set to <literal>isolate</literal>,
+        only a single unit may be listed in
+        <varname>OnFailure=</varname>..</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>IgnoreOnIsolate=</varname></term>
+
+        <listitem><para>Takes a boolean argument. If <option>true</option>, this unit
+        will not be stopped when isolating another unit. Defaults to
+        <option>false</option> for service, target, socket, busname, timer, and path
+        units, and <option>true</option> for slice, scope, device, swap, mount, and
+        automount units.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>StopWhenUnneeded=</varname></term>
+
+        <listitem><para>Takes a boolean argument. If
+        <option>true</option>, this unit will be stopped when it is no
+        longer used. Note that, in order to minimize the work to be
+        executed, systemd will not stop units by default unless they
+        are conflicting with other units, or the user explicitly
+        requested their shut down. If this option is set, a unit will
+        be automatically cleaned up if no other active unit requires
+        it. Defaults to <option>false</option>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>RefuseManualStart=</varname></term>
+        <term><varname>RefuseManualStop=</varname></term>
+
+        <listitem><para>Takes a boolean argument. If
+        <option>true</option>, this unit can only be activated or
+        deactivated indirectly. In this case, explicit start-up or
+        termination requested by the user is denied, however if it is
+        started or stopped as a dependency of another unit, start-up
+        or termination will succeed. This is mostly a safety feature
+        to ensure that the user does not accidentally activate units
+        that are not intended to be activated explicitly, and not
+        accidentally deactivate units that are not intended to be
+        deactivated. These options default to
+        <option>false</option>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>AllowIsolate=</varname></term>
+
+        <listitem><para>Takes a boolean argument. If
+        <option>true</option>, this unit may be used with the
+        <command>systemctl isolate</command> command. Otherwise, this
+        will be refused. It probably is a good idea to leave this
+        disabled except for target units that shall be used similar to
+        runlevels in SysV init systems, just as a precaution to avoid
+        unusable system states. This option defaults to
+        <option>false</option>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>DefaultDependencies=</varname></term>
+
+        <listitem><para>Takes a boolean argument. If
+        <option>true</option>, (the default), a few default
+        dependencies will implicitly be created for the unit. The
+        actual dependencies created depend on the unit type. For
+        example, for service units, these dependencies ensure that the
+        service is started only after basic system initialization is
+        completed and is properly terminated on system shutdown. See
+        the respective man pages for details. Generally, only services
+        involved with early boot or late shutdown should set this
+        option to <option>false</option>. It is highly recommended to
+        leave this option enabled for the majority of common units. If
+        set to <option>false</option>, this option does not disable
+        all implicit dependencies, just non-essential
+        ones.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>CollectMode=</varname></term>
+
+        <listitem><para>Tweaks the "garbage collection" algorithm for this unit. Takes one of <option>inactive</option>
+        or <option>inactive-or-failed</option>. If set to <option>inactive</option> the unit will be unloaded if it is
+        in the <constant>inactive</constant> state and is not referenced by clients, jobs or other units — however it
+        is not unloaded if it is in the <constant>failed</constant> state. In <option>failed</option> mode, failed
+        units are not unloaded until the user invoked <command>systemctl reset-failed</command> on them to reset the
+        <constant>failed</constant> state, or an equivalent command. This behaviour is altered if this option is set to
+        <option>inactive-or-failed</option>: in this case the unit is unloaded even if the unit is in a
+        <constant>failed</constant> state, and thus an explicitly resetting of the <constant>failed</constant> state is
+        not necessary. Note that if this mode is used unit results (such as exit codes, exit signals, consumed
+        resources, …) are flushed out immediately after the unit completed, except for what is stored in the logging
+        subsystem. Defaults to <option>inactive</option>.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>FailureAction=</varname></term>
+        <term><varname>SuccessAction=</varname></term>
+
+        <listitem><para>Configure the action to take when the unit stops and enters a failed state or inactive state.
+        Takes one of <option>none</option>, <option>reboot</option>, <option>reboot-force</option>,
+        <option>reboot-immediate</option>, <option>poweroff</option>, <option>poweroff-force</option>,
+        <option>poweroff-immediate</option>, <option>exit</option>, and <option>exit-force</option>. In system mode,
+        all options are allowed. In user mode, only <option>none</option>, <option>exit</option>, and
+        <option>exit-force</option> are allowed. Both options default to <option>none</option>.</para>
+
+        <para>If <option>none</option> is set, no action will be triggered. <option>reboot</option> causes a reboot
+        following the normal shutdown procedure (i.e. equivalent to <command>systemctl reboot</command>).
+        <option>reboot-force</option> causes a forced reboot which will terminate all processes forcibly but should
+        cause no dirty file systems on reboot (i.e. equivalent to <command>systemctl reboot -f</command>) and
+        <option>reboot-immediate</option> causes immediate execution of the
+        <citerefentry><refentrytitle>reboot</refentrytitle><manvolnum>2</manvolnum></citerefentry> system call, which
+        might result in data loss (i.e. equivalent to <command>systemctl reboot -ff</command>). Similarly,
+        <option>poweroff</option>, <option>poweroff-force</option>, <option>poweroff-immediate</option> have the effect
+        of powering down the system with similar semantics. <option>exit</option> causes the manager to exit following
+        the normal shutdown procedure, and <option>exit-force</option> causes it terminate without shutting down
+        services. When <option>exit</option> or <option>exit-force</option> is used by default the exit status of the
+        main process of the unit (if this applies) is returned from the service manager. However, this may be overriden
+        with <varname>FailureActionExitStatus=</varname>/<varname>SuccessActionExitStatus=</varname>, see
+        below.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>FailureActionExitStatus=</varname></term>
+        <term><varname>SuccessActionExitStatus=</varname></term>
+
+        <listitem><para>Controls the exit status to propagate back to an invoking container manager (in case of a
+        system service) or service manager (in case of a user manager) when the
+        <varname>FailureAction=</varname>/<varname>SuccessAction=</varname> are set to <option>exit</option> or
+        <option>exit-force</option> and the action is triggered. By default the exit status of the main process of the
+        triggering unit (if this applies) is propagated. Takes a value in the range 0…255 or the empty string to
+        request default behaviour.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>JobTimeoutSec=</varname></term>
+        <term><varname>JobRunningTimeoutSec=</varname></term>
+
+        <listitem><para>When a job for this unit is queued, a timeout <varname>JobTimeoutSec=</varname> may be
+        configured. Similarly, <varname>JobRunningTimeoutSec=</varname> starts counting when the queued job is actually
+        started. If either time limit is reached, the job will be cancelled, the unit however will not change state or
+        even enter the <literal>failed</literal> mode. This value defaults to <literal>infinity</literal> (job timeouts
+        disabled), except for device units (<varname>JobRunningTimeoutSec=</varname> defaults to
+        <varname>DefaultTimeoutStartSec=</varname>). NB: this timeout is independent from any unit-specific timeout
+        (for example, the timeout set with <varname>TimeoutStartSec=</varname> in service units) as the job timeout has
+        no effect on the unit itself, only on the job that might be pending for it. Or in other words: unit-specific
+        timeouts are useful to abort unit state changes, and revert them. The job timeout set with this option however
+        is useful to abort only the job waiting for the unit state to change.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>JobTimeoutAction=</varname></term>
+        <term><varname>JobTimeoutRebootArgument=</varname></term>
+
+        <listitem><para><varname>JobTimeoutAction=</varname> optionally configures an additional action to take when
+        the timeout is hit, see description of <varname>JobTimeoutSec=</varname> and
+        <varname>JobRunningTimeoutSec=</varname> above. It takes the same values as
+        <varname>StartLimitAction=</varname>. Defaults to <option>none</option>.
+        <varname>JobTimeoutRebootArgument=</varname> configures an optional reboot string to pass to the
+        <citerefentry><refentrytitle>reboot</refentrytitle><manvolnum>2</manvolnum></citerefentry> system call.
+        </para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>StartLimitIntervalSec=<replaceable>interval</replaceable></varname></term>
+        <term><varname>StartLimitBurst=<replaceable>burst</replaceable></varname></term>
+
+        <listitem><para>Configure unit start rate limiting. Units which are started more than
+        <replaceable>burst</replaceable> times within an <replaceable>interval</replaceable> time interval are not
+        permitted to start any more. Use <varname>StartLimitIntervalSec=</varname> to configure the checking interval
+        (defaults to <varname>DefaultStartLimitIntervalSec=</varname> in manager configuration file, set it to 0 to
+        disable any kind of rate limiting). Use <varname>StartLimitBurst=</varname> to configure how many starts per
+        interval are allowed (defaults to <varname>DefaultStartLimitBurst=</varname> in manager configuration
+        file). These configuration options are particularly useful in conjunction with the service setting
+        <varname>Restart=</varname> (see
+        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>); however,
+        they apply to all kinds of starts (including manual), not just those triggered by the
+        <varname>Restart=</varname> logic. Note that units which are configured for <varname>Restart=</varname> and
+        which reach the start limit are not attempted to be restarted anymore; however, they may still be restarted
+        manually at a later point, after the <replaceable>interval</replaceable> has passed.  From this point on, the
+        restart logic is activated again. Note that <command>systemctl reset-failed</command> will cause the restart
+        rate counter for a service to be flushed, which is useful if the administrator wants to manually start a unit
+        and the start limit interferes with that. Note that this rate-limiting is enforced after any unit condition
+        checks are executed, and hence unit activations with failing conditions do not count towards this rate
+        limit. This setting does not apply to slice, target, device, and scope units, since they are unit types whose
+        activation may either never fail, or may succeed only a single time.</para>
+
+        <para>When a unit is unloaded due to the garbage collection logic (see above) its rate limit counters are
+        flushed out too. This means that configuring start rate limiting for a unit that is not referenced continuously
+        has no effect.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>StartLimitAction=</varname></term>
+
+        <listitem><para>Configure an additional action to take if the rate limit configured with
+        <varname>StartLimitIntervalSec=</varname> and <varname>StartLimitBurst=</varname> is hit.  Takes the same
+        values as the setting <varname>FailureAction=</varname>/<varname>SuccessAction=</varname> settings and executes
+        the same actions. If <option>none</option> is set, hitting the rate limit will trigger no action besides that
+        the start will not be permitted. Defaults to <option>none</option>.</para></listitem>
+      </varlistentry>
+
+
+      <varlistentry>
+        <term><varname>RebootArgument=</varname></term>
+        <listitem><para>Configure the optional argument for the
+        <citerefentry><refentrytitle>reboot</refentrytitle><manvolnum>2</manvolnum></citerefentry> system call if
+        <varname>StartLimitAction=</varname> or <varname>FailureAction=</varname> is a reboot action. This
+        works just like the optional argument to <command>systemctl reboot</command> command.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>ConditionArchitecture=</varname></term>
+        <term><varname>ConditionVirtualization=</varname></term>
+        <term><varname>ConditionHost=</varname></term>
+        <term><varname>ConditionKernelCommandLine=</varname></term>
+        <term><varname>ConditionKernelVersion=</varname></term>
+        <term><varname>ConditionSecurity=</varname></term>
+        <term><varname>ConditionCapability=</varname></term>
+        <term><varname>ConditionACPower=</varname></term>
+        <term><varname>ConditionNeedsUpdate=</varname></term>
+        <term><varname>ConditionFirstBoot=</varname></term>
+        <term><varname>ConditionPathExists=</varname></term>
+        <term><varname>ConditionPathExistsGlob=</varname></term>
+        <term><varname>ConditionPathIsDirectory=</varname></term>
+        <term><varname>ConditionPathIsSymbolicLink=</varname></term>
+        <term><varname>ConditionPathIsMountPoint=</varname></term>
+        <term><varname>ConditionPathIsReadWrite=</varname></term>
+        <term><varname>ConditionDirectoryNotEmpty=</varname></term>
+        <term><varname>ConditionFileNotEmpty=</varname></term>
+        <term><varname>ConditionFileIsExecutable=</varname></term>
+        <term><varname>ConditionUser=</varname></term>
+        <term><varname>ConditionGroup=</varname></term>
+        <term><varname>ConditionControlGroupController=</varname></term>
+
+        <!-- We do not document ConditionNull=
+             here, as it is not particularly
+             useful and probably just
+             confusing. -->
+
+        <listitem><para>Before starting a unit, verify that the specified condition is true. If it is not true, the
+        starting of the unit will be (mostly silently) skipped, however all ordering dependencies of it are still
+        respected. A failing condition will not result in the unit being moved into the <literal>failed</literal>
+        state. The condition is checked at the time the queued start job is to be executed. Use condition expressions
+        in order to silently skip units that do not apply to the local running system, for example because the kernel
+        or runtime environment doesn't require their functionality. Use the various
+        <varname>AssertArchitecture=</varname>, <varname>AssertVirtualization=</varname>, … options for a similar
+        mechanism that causes the job to fail (instead of being skipped) and results in logging about the failed check
+        (instead of being silently processed). For details about assertion conditions see below.</para>
+
+        <para><varname>ConditionArchitecture=</varname> may be used to
+        check whether the system is running on a specific
+        architecture. Takes one of
+        <varname>x86</varname>,
+        <varname>x86-64</varname>,
+        <varname>ppc</varname>,
+        <varname>ppc-le</varname>,
+        <varname>ppc64</varname>,
+        <varname>ppc64-le</varname>,
+        <varname>ia64</varname>,
+        <varname>parisc</varname>,
+        <varname>parisc64</varname>,
+        <varname>s390</varname>,
+        <varname>s390x</varname>,
+        <varname>sparc</varname>,
+        <varname>sparc64</varname>,
+        <varname>mips</varname>,
+        <varname>mips-le</varname>,
+        <varname>mips64</varname>,
+        <varname>mips64-le</varname>,
+        <varname>alpha</varname>,
+        <varname>arm</varname>,
+        <varname>arm-be</varname>,
+        <varname>arm64</varname>,
+        <varname>arm64-be</varname>,
+        <varname>sh</varname>,
+        <varname>sh64</varname>,
+        <varname>m68k</varname>,
+        <varname>tilegx</varname>,
+        <varname>cris</varname>,
+        <varname>arc</varname>,
+        <varname>arc-be</varname> to test
+        against a specific architecture. The architecture is
+        determined from the information returned by
+        <citerefentry project='man-pages'><refentrytitle>uname</refentrytitle><manvolnum>2</manvolnum></citerefentry>
+        and is thus subject to
+        <citerefentry><refentrytitle>personality</refentrytitle><manvolnum>2</manvolnum></citerefentry>.
+        Note that a <varname>Personality=</varname> setting in the
+        same unit file has no effect on this condition. A special
+        architecture name <varname>native</varname> is mapped to the
+        architecture the system manager itself is compiled for. The
+        test may be negated by prepending an exclamation mark.</para>
+
+        <para><varname>ConditionVirtualization=</varname> may be used
+        to check whether the system is executed in a virtualized
+        environment and optionally test whether it is a specific
+        implementation. Takes either boolean value to check if being
+        executed in any virtualized environment, or one of
+        <varname>vm</varname> and
+        <varname>container</varname> to test against a generic type of
+        virtualization solution, or one of
+        <varname>qemu</varname>,
+        <varname>kvm</varname>,
+        <varname>zvm</varname>,
+        <varname>vmware</varname>,
+        <varname>microsoft</varname>,
+        <varname>oracle</varname>,
+        <varname>xen</varname>,
+        <varname>bochs</varname>,
+        <varname>uml</varname>,
+        <varname>bhyve</varname>,
+        <varname>qnx</varname>,
+        <varname>openvz</varname>,
+        <varname>lxc</varname>,
+        <varname>lxc-libvirt</varname>,
+        <varname>systemd-nspawn</varname>,
+        <varname>docker</varname>,
+        <varname>rkt</varname> to test
+        against a specific implementation, or
+        <varname>private-users</varname> to check whether we are running in a user namespace. See
+        <citerefentry><refentrytitle>systemd-detect-virt</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+        for a full list of known virtualization technologies and their
+        identifiers. If multiple virtualization technologies are
+        nested, only the innermost is considered. The test may be
+        negated by prepending an exclamation mark.</para>
+
+        <para><varname>ConditionHost=</varname> may be used to match
+        against the hostname or machine ID of the host. This either
+        takes a hostname string (optionally with shell style globs)
+        which is tested against the locally set hostname as returned
+        by
+        <citerefentry><refentrytitle>gethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
+        or a machine ID formatted as string (see
+        <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
+        The test may be negated by prepending an exclamation
+        mark.</para>
+
+        <para><varname>ConditionKernelCommandLine=</varname> may be
+        used to check whether a specific kernel command line option is
+        set (or if prefixed with the exclamation mark unset). The
+        argument must either be a single word, or an assignment (i.e.
+        two words, separated <literal>=</literal>). In the former case
+        the kernel command line is searched for the word appearing as
+        is, or as left hand side of an assignment. In the latter case,
+        the exact assignment is looked for with right and left hand
+        side matching.</para>
+
+        <para><varname>ConditionKernelVersion=</varname> may be used to check whether the kernel version (as reported
+        by <command>uname -r</command>) matches a certain expression (or if prefixed with the exclamation mark does not
+        match it). The argument must be a single string. If the string starts with one of <literal>&lt;</literal>,
+        <literal>&lt;=</literal>, <literal>=</literal>, <literal>&gt;=</literal>, <literal>&gt;</literal> a relative
+        version comparison is done, otherwise the specified string is matched with shell-style globs.</para>
+
+        <para>Note that using the kernel version string is an unreliable way to determine which features are supported
+        by a kernel, because of the widespread practice of backporting drivers, features, and fixes from newer upstream
+        kernels into older versions provided by distributions. Hence, this check is inherently unportable and should
+        not be used for units which may be used on different distributions.</para>
+
+        <para><varname>ConditionSecurity=</varname> may be used to check
+        whether the given security technology is enabled on the
+        system. Currently, the recognized values are
+        <varname>selinux</varname>, <varname>apparmor</varname>,
+        <varname>tomoyo</varname>, <varname>ima</varname>,
+        <varname>smack</varname>, <varname>audit</varname> and
+        <varname>uefi-secureboot</varname>. The test may be negated by
+        prepending an exclamation mark.</para>
+
+        <para><varname>ConditionCapability=</varname> may be used to
+        check whether the given capability exists in the capability
+        bounding set of the service manager (i.e. this does not check
+        whether capability is actually available in the permitted or
+        effective sets, see
+        <citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+        for details). Pass a capability name such as
+        <literal>CAP_MKNOD</literal>, possibly prefixed with an
+        exclamation mark to negate the check.</para>
+
+        <para><varname>ConditionACPower=</varname> may be used to
+        check whether the system has AC power, or is exclusively
+        battery powered at the time of activation of the unit. This
+        takes a boolean argument. If set to <varname>true</varname>,
+        the condition will hold only if at least one AC connector of
+        the system is connected to a power source, or if no AC
+        connectors are known. Conversely, if set to
+        <varname>false</varname>, the condition will hold only if
+        there is at least one AC connector known and all AC connectors
+        are disconnected from a power source.</para>
+
+        <para><varname>ConditionNeedsUpdate=</varname> takes one of
+        <filename>/var</filename> or <filename>/etc</filename> as
+        argument, possibly prefixed with a <literal>!</literal> (for
+        inverting the condition). This condition may be used to
+        conditionalize units on whether the specified directory
+        requires an update because <filename>/usr</filename>'s
+        modification time is newer than the stamp file
+        <filename>.updated</filename> in the specified directory. This
+        is useful to implement offline updates of the vendor operating
+        system resources in <filename>/usr</filename> that require
+        updating of <filename>/etc</filename> or
+        <filename>/var</filename> on the next following boot. Units
+        making use of this condition should order themselves before
+        <citerefentry><refentrytitle>systemd-update-done.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+        to make sure they run before the stamp file's modification
+        time gets reset indicating a completed update.</para>
+
+        <para><varname>ConditionFirstBoot=</varname> takes a boolean argument. This condition may be used to
+        conditionalize units on whether the system is booting up with an unpopulated <filename>/etc</filename>
+        directory (specifically: an <filename>/etc</filename> with no <filename>/etc/machine-id</filename>). This may
+        be used to populate <filename>/etc</filename> on the first boot after factory reset, or when a new system
+        instance boots up for the first time.</para>
+
+        <para>With <varname>ConditionPathExists=</varname> a file
+        existence condition is checked before a unit is started. If
+        the specified absolute path name does not exist, the condition
+        will fail. If the absolute path name passed to
+        <varname>ConditionPathExists=</varname> is prefixed with an
+        exclamation mark (<literal>!</literal>), the test is negated,
+        and the unit is only started if the path does not
+        exist.</para>
+
+        <para><varname>ConditionPathExistsGlob=</varname> is similar
+        to <varname>ConditionPathExists=</varname>, but checks for the
+        existence of at least one file or directory matching the
+        specified globbing pattern.</para>
+
+        <para><varname>ConditionPathIsDirectory=</varname> is similar
+        to <varname>ConditionPathExists=</varname> but verifies
+        whether a certain path exists and is a directory.</para>
+
+        <para><varname>ConditionPathIsSymbolicLink=</varname> is
+        similar to <varname>ConditionPathExists=</varname> but
+        verifies whether a certain path exists and is a symbolic
+        link.</para>
+
+        <para><varname>ConditionPathIsMountPoint=</varname> is similar
+        to <varname>ConditionPathExists=</varname> but verifies
+        whether a certain path exists and is a mount point.</para>
+
+        <para><varname>ConditionPathIsReadWrite=</varname> is similar
+        to <varname>ConditionPathExists=</varname> but verifies
+        whether the underlying file system is readable and writable
+        (i.e. not mounted read-only).</para>
+
+        <para><varname>ConditionDirectoryNotEmpty=</varname> is
+        similar to <varname>ConditionPathExists=</varname> but
+        verifies whether a certain path exists and is a non-empty
+        directory.</para>
+
+        <para><varname>ConditionFileNotEmpty=</varname> is similar to
+        <varname>ConditionPathExists=</varname> but verifies whether a
+        certain path exists and refers to a regular file with a
+        non-zero size.</para>
+
+        <para><varname>ConditionFileIsExecutable=</varname> is similar
+        to <varname>ConditionPathExists=</varname> but verifies
+        whether a certain path exists, is a regular file and marked
+        executable.</para>
+
+        <para><varname>ConditionUser=</varname> takes a numeric
+        <literal>UID</literal>, a UNIX user name, or the special value
+        <literal>@system</literal>. This condition may be used to check
+        whether the service manager is running as the given user. The
+        special value <literal>@system</literal> can be used to check
+        if the user id is within the system user range. This option is not
+        useful for system services, as the system manager exclusively
+        runs as the root user, and thus the test result is constant.</para>
+
+        <para><varname>ConditionGroup=</varname> is similar
+        to <varname>ConditionUser=</varname> but verifies that the
+        service manager's real or effective group, or any of its
+        auxiliary groups match the specified group or GID. This setting
+        does not have a special value <literal>@system</literal>.</para>
+
+        <para><varname>ConditionControlGroupController=</varname> takes a
+        cgroup controller name (eg. <option>cpu</option>), verifying that it is
+        available for use on the system. For example, a particular controller
+        may not be available if it was disabled on the kernel command line with
+        <varname>cgroup_disable=controller</varname>. Multiple controllers may
+        be passed with a space separating them; in this case the condition will
+        only pass if all listed controllers are available for use. Controllers
+        unknown to systemd are ignored. Valid controllers are
+        <option>cpu</option>, <option>cpuacct</option>, <option>io</option>,
+        <option>blkio</option>, <option>memory</option>,
+        <option>devices</option>, and <option>pids</option>.</para>
+
+        <para>If multiple conditions are specified, the unit will be
+        executed if all of them apply (i.e. a logical AND is applied).
+        Condition checks can be prefixed with a pipe symbol (|) in
+        which case a condition becomes a triggering condition. If at
+        least one triggering condition is defined for a unit, then the
+        unit will be executed if at least one of the triggering
+        conditions apply and all of the non-triggering conditions. If
+        you prefix an argument with the pipe symbol and an exclamation
+        mark, the pipe symbol must be passed first, the exclamation
+        second. Except for
+        <varname>ConditionPathIsSymbolicLink=</varname>, all path
+        checks follow symlinks. If any of these options is assigned
+        the empty string, the list of conditions is reset completely,
+        all previous condition settings (of any kind) will have no
+        effect.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>AssertArchitecture=</varname></term>
+        <term><varname>AssertVirtualization=</varname></term>
+        <term><varname>AssertHost=</varname></term>
+        <term><varname>AssertKernelCommandLine=</varname></term>
+        <term><varname>AssertKernelVersion=</varname></term>
+        <term><varname>AssertSecurity=</varname></term>
+        <term><varname>AssertCapability=</varname></term>
+        <term><varname>AssertACPower=</varname></term>
+        <term><varname>AssertNeedsUpdate=</varname></term>
+        <term><varname>AssertFirstBoot=</varname></term>
+        <term><varname>AssertPathExists=</varname></term>
+        <term><varname>AssertPathExistsGlob=</varname></term>
+        <term><varname>AssertPathIsDirectory=</varname></term>
+        <term><varname>AssertPathIsSymbolicLink=</varname></term>
+        <term><varname>AssertPathIsMountPoint=</varname></term>
+        <term><varname>AssertPathIsReadWrite=</varname></term>
+        <term><varname>AssertDirectoryNotEmpty=</varname></term>
+        <term><varname>AssertFileNotEmpty=</varname></term>
+        <term><varname>AssertFileIsExecutable=</varname></term>
+        <term><varname>AssertUser=</varname></term>
+        <term><varname>AssertGroup=</varname></term>
+        <term><varname>AssertControlGroupController=</varname></term>
+
+        <listitem><para>Similar to the <varname>ConditionArchitecture=</varname>,
+        <varname>ConditionVirtualization=</varname>, …, condition settings described above, these settings add
+        assertion checks to the start-up of the unit. However, unlike the conditions settings, any assertion setting
+        that is not met results in failure of the start job (which means this is logged loudly). Note that hitting a
+        configured assertion does not cause the unit to enter the <literal>failed</literal> state (or in fact result in
+        any state change of the unit), it affects only the job queued for it. Use assertion expressions for units that
+        cannot operate when specific requirements are not met, and when this is something the administrator or user
+        should look into.</para>
+
+        <para>Note that neither assertion nor condition expressions result in unit state changes. Also note that both
+        are checked at the time the job is to be executed, i.e. long after depending jobs and it itself were
+        queued. Thus, neither condition nor assertion expressions are suitable for conditionalizing unit
+        dependencies.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>SourcePath=</varname></term>
+        <listitem><para>A path to a configuration file this unit has
+        been generated from. This is primarily useful for
+        implementation of generator tools that convert configuration
+        from an external configuration file format into native unit
+        files. This functionality should not be used in normal
+        units.</para></listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Mapping of unit properties to their inverses</title>
+
+    <para>Unit settings that create a relationship with a second unit usually show up
+    in properties of both units, for example in <command>systemctl show</command>
+    output. In some cases the name of the property is the same as the name of the
+    configuration setting, but not always. This table lists the properties
+    that are shown on two units which are connected through some dependency, and shows
+    which property on "source" unit corresponds to which property on the "target" unit.
+    </para>
+
+    <table>
+      <title>
+        "Forward" and "reverse" unit properties
+      </title>
+
+      <tgroup cols='2'>
+        <colspec colname='forward' />
+        <colspec colname='reverse' />
+        <colspec colname='notes' />
+        <thead>
+          <row>
+            <entry>"Forward" property</entry>
+            <entry>"Reverse" property</entry>
+            <entry>Where used</entry>
+          </row>
+        </thead>
+        <tbody>
+          <row>
+            <entry><varname>Before=</varname></entry>
+            <entry><varname>After=</varname></entry>
+            <entry morerows='1' valign='middle'>Both are unit file options</entry>
+          </row>
+          <row>
+            <entry><varname>After=</varname></entry>
+            <entry><varname>Before=</varname></entry>
+          </row>
+          <row>
+            <entry><varname>Requires=</varname></entry>
+            <entry><varname>RequiredBy=</varname></entry>
+            <entry>A unit file option; an option in the [Install] section</entry>
+          </row>
+          <row>
+            <entry><varname>Wants=</varname></entry>
+            <entry><varname>WantedBy=</varname></entry>
+            <entry>A unit file option; an option in the [Install] section</entry>
+          </row>
+          <row>
+            <entry><varname>PartOf=</varname></entry>
+            <entry><varname>ConsistsOf=</varname></entry>
+            <entry>A unit file option; an automatic property</entry>
+          </row>
+          <row>
+            <entry><varname>BindsTo=</varname></entry>
+            <entry><varname>BoundBy=</varname></entry>
+            <entry>A unit file option; an automatic property</entry>
+          </row>
+          <row>
+            <entry><varname>Requisite=</varname></entry>
+            <entry><varname>RequisiteOf=</varname></entry>
+            <entry>A unit file option; an automatic property</entry>
+          </row>
+          <row>
+            <entry><varname>Triggers=</varname></entry>
+            <entry><varname>TriggeredBy=</varname></entry>
+            <entry>Automatic properties, see notes below</entry>
+          </row>
+          <row>
+            <entry><varname>Conflicts=</varname></entry>
+            <entry><varname>ConflictedBy=</varname></entry>
+            <entry>A unit file option; an automatic property</entry>
+          </row>
+          <row>
+            <entry><varname>PropagatesReloadTo=</varname></entry>
+            <entry><varname>ReloadPropagatedFrom=</varname></entry>
+            <entry morerows='1' valign='middle'>Both are unit file options</entry>
+          </row>
+          <row>
+            <entry><varname>ReloadPropagatedFrom=</varname></entry>
+            <entry><varname>PropagatesReloadTo=</varname></entry>
+          </row>
+          <row>
+            <entry><varname>Following=</varname></entry>
+            <entry>n/a</entry>
+            <entry>An automatic property</entry>
+          </row>
+        </tbody>
+      </tgroup>
+    </table>
+
+    <para>Note: <varname>WantedBy=</varname> and <varname>RequiredBy=</varname> are
+    used in the [Install] section to create symlinks in <filename>.wants/</filename>
+    and <filename>.requires/</filename> directories. They cannot be used directly as a
+    unit configuration setting.</para>
+
+    <para>Note: <varname>ConsistsOf=</varname>, <varname>BoundBy=</varname>,
+    <varname>RequisiteOf=</varname>, <varname>ConflictedBy=</varname> are created
+    implicitly along with their reverse and cannot be specified directly.</para>
+
+    <para>Note: <varname>Triggers=</varname> is created implicitly between a socket,
+    path unit, or an automount unit, and the unit they activate. By default a unit
+    with the same name is triggered, but this can be overridden using
+    <varname>Sockets=</varname>, <varname>Service=</varname>, and <varname>Unit=</varname>
+    settings. See
+    <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    and
+    <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for details. <varname>TriggersBy=</varname> is created implicitly on the
+    triggered unit.</para>
+
+    <para>Note: <varname>Following=</varname> is used to group device aliases and points to the
+    "primary" device unit that systemd is using to track device state, usually corresponding to a
+    sysfs path. It does not show up in the "target" unit.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>[Install] Section Options</title>
+
+    <para>Unit files may include an <literal>[Install]</literal> section, which carries installation information for
+    the unit. This section is not interpreted by
+    <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> during runtime; it is
+    used by the <command>enable</command> and <command>disable</command> commands of the
+    <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> tool during
+    installation of a unit.</para>
+
+    <variablelist class='unit-directives'>
+      <varlistentry>
+        <term><varname>Alias=</varname></term>
+
+        <listitem><para>A space-separated list of additional names this unit shall be installed under. The names listed
+        here must have the same suffix (i.e. type) as the unit filename. This option may be specified more than once,
+        in which case all listed names are used. At installation time, <command>systemctl enable</command> will create
+        symlinks from these names to the unit filename. Note that not all unit types support such alias names, and this
+        setting is not supported for them. Specifically, mount, slice, swap, and automount units do not support
+        aliasing.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>WantedBy=</varname></term>
+        <term><varname>RequiredBy=</varname></term>
+
+        <listitem><para>This option may be used more than once, or a
+        space-separated list of unit names may be given. A symbolic
+        link is created in the <filename>.wants/</filename> or
+        <filename>.requires/</filename> directory of each of the
+        listed units when this unit is installed by <command>systemctl
+        enable</command>. This has the effect that a dependency of
+        type <varname>Wants=</varname> or <varname>Requires=</varname>
+        is added from the listed unit to the current unit. The primary
+        result is that the current unit will be started when the
+        listed unit is started. See the description of
+        <varname>Wants=</varname> and <varname>Requires=</varname> in
+        the [Unit] section for details.</para>
+
+        <para><command>WantedBy=foo.service</command> in a service
+        <filename>bar.service</filename> is mostly equivalent to
+        <command>Alias=foo.service.wants/bar.service</command> in the
+        same file. In case of template units, <command>systemctl
+        enable</command> must be called with an instance name, and
+        this instance will be added to the
+        <filename>.wants/</filename> or
+        <filename>.requires/</filename> list of the listed unit. E.g.
+        <command>WantedBy=getty.target</command> in a service
+        <filename>getty@.service</filename> will result in
+        <command>systemctl enable getty@tty2.service</command>
+        creating a
+        <filename>getty.target.wants/getty@tty2.service</filename>
+        link to <filename>getty@.service</filename>.
+        </para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>Also=</varname></term>
+
+        <listitem><para>Additional units to install/deinstall when
+        this unit is installed/deinstalled. If the user requests
+        installation/deinstallation of a unit with this option
+        configured, <command>systemctl enable</command> and
+        <command>systemctl disable</command> will automatically
+        install/uninstall units listed in this option as well.</para>
+
+        <para>This option may be used more than once, or a
+        space-separated list of unit names may be
+        given.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>DefaultInstance=</varname></term>
+
+        <listitem><para>In template unit files, this specifies for
+        which instance the unit shall be enabled if the template is
+        enabled without any explicitly set instance. This option has
+        no effect in non-template unit files. The specified string
+        must be usable as instance identifier.</para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <para>The following specifiers are interpreted in the Install
+    section: %n, %N, %p, %i, %j, %g, %G, %U, %u, %m, %H, %b, %v. For their
+    meaning see the next section.
+    </para>
+  </refsect1>
+
+  <refsect1>
+    <title>Specifiers</title>
+
+    <para>Many settings resolve specifiers which may be used to write
+    generic unit files referring to runtime or unit parameters that
+    are replaced when the unit files are loaded. Specifiers must be known
+    and resolvable for the setting to be valid. The following
+    specifiers are understood:</para>
+
+    <table>
+      <title>Specifiers available in unit files</title>
+      <tgroup cols='3' align='left' colsep='1' rowsep='1'>
+        <colspec colname="spec" />
+        <colspec colname="mean" />
+        <colspec colname="detail" />
+        <thead>
+          <row>
+            <entry>Specifier</entry>
+            <entry>Meaning</entry>
+            <entry>Details</entry>
+          </row>
+        </thead>
+        <tbody>
+          <row>
+            <entry><literal>%b</literal></entry>
+            <entry>Boot ID</entry>
+            <entry>The boot ID of the running system, formatted as string. See <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> for more information.</entry>
+          </row>
+          <row>
+            <entry><literal>%C</literal></entry>
+            <entry>Cache directory root</entry>
+            <entry>This is either <filename>/var/cache</filename> (for the system manager) or the path <literal>$XDG_CACHE_HOME</literal> resolves to (for user managers).</entry>
+          </row>
+          <row>
+            <entry><literal>%E</literal></entry>
+            <entry>Configuration directory root</entry>
+            <entry>This is either <filename>/etc</filename> (for the system manager) or the path <literal>$XDG_CONFIG_HOME</literal> resolves to (for user managers).</entry>
+          </row>
+          <row>
+            <entry><literal>%f</literal></entry>
+            <entry>Unescaped filename</entry>
+            <entry>This is either the unescaped instance name (if applicable) with <filename>/</filename> prepended (if applicable), or the unescaped prefix name prepended with <filename>/</filename>. This implements unescaping according to the rules for escaping absolute file system paths discussed above.</entry>
+          </row>
+          <row>
+            <entry><literal>%h</literal></entry>
+            <entry>User home directory</entry>
+            <entry>This is the home directory of the user running the service manager instance. In case of the system manager this resolves to <literal>/root</literal>.</entry>
+          </row>
+          <row>
+            <entry><literal>%H</literal></entry>
+            <entry>Host name</entry>
+            <entry>The hostname of the running system at the point in time the unit configuration is loaded.</entry>
+          </row>
+          <row>
+            <entry><literal>%i</literal></entry>
+            <entry>Instance name</entry>
+            <entry>For instantiated units this is the string between the first <literal>@</literal> character and the type suffix. Empty for non-instantiated units.</entry>
+          </row>
+          <row>
+            <entry><literal>%I</literal></entry>
+            <entry>Unescaped instance name</entry>
+            <entry>Same as <literal>%i</literal>, but with escaping undone.</entry>
+          </row>
+          <row>
+            <entry><literal>%j</literal></entry>
+            <entry>Final component of the prefix</entry>
+            <entry>This is the string between the last <literal>-</literal> and the end of the prefix name. If there is no <literal>-</literal>, this is the same as <literal>%p</literal>.</entry>
+          </row>
+          <row>
+            <entry><literal>%J</literal></entry>
+            <entry>Unescaped final component of the prefix</entry>
+            <entry>Same as <literal>%j</literal>, but with escaping undone.</entry>
+          </row>
+          <row>
+            <entry><literal>%L</literal></entry>
+            <entry>Log directory root</entry>
+            <entry>This is either <filename>/var/log</filename> (for the system manager) or the path <literal>$XDG_CONFIG_HOME</literal> resolves to with <filename noindex='true'>/log</filename> appended (for user managers).</entry>
+          </row>
+          <row>
+            <entry><literal>%m</literal></entry>
+            <entry>Machine ID</entry>
+            <entry>The machine ID of the running system, formatted as string. See <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more information.</entry>
+          </row>
+          <row>
+            <entry><literal>%n</literal></entry>
+            <entry>Full unit name</entry>
+            <entry></entry>
+          </row>
+          <row>
+            <entry><literal>%N</literal></entry>
+            <entry>Full unit name</entry>
+            <entry>Same as <literal>%n</literal>, but with the type suffix removed.</entry>
+          </row>
+          <row>
+            <entry><literal>%p</literal></entry>
+            <entry>Prefix name</entry>
+            <entry>For instantiated units, this refers to the string before the first <literal>@</literal> character of the unit name. For non-instantiated units, same as <literal>%N</literal>.</entry>
+          </row>
+          <row>
+            <entry><literal>%P</literal></entry>
+            <entry>Unescaped prefix name</entry>
+            <entry>Same as <literal>%p</literal>, but with escaping undone.</entry>
+          </row>
+          <row>
+            <entry><literal>%s</literal></entry>
+            <entry>User shell</entry>
+            <entry>This is the shell of the user running the service manager instance. In case of the system manager this resolves to <literal>/bin/sh</literal>.</entry>
+          </row>
+          <row>
+            <entry><literal>%S</literal></entry>
+            <entry>State directory root</entry>
+            <entry>This is either <filename>/var/lib</filename> (for the system manager) or the path <literal>$XDG_CONFIG_HOME</literal> resolves to (for user managers).</entry>
+          </row>
+          <row>
+            <entry><literal>%t</literal></entry>
+            <entry>Runtime directory root</entry>
+            <entry>This is either <filename>/run</filename> (for the system manager) or the path <literal>$XDG_RUNTIME_DIR</literal> resolves to (for user managers).</entry>
+          </row>
+          <row>
+            <entry><literal>%T</literal></entry>
+            <entry>Directory for temporary files</entry>
+            <entry>This is either <filename>/tmp</filename> or the path <literal>$TMPDIR</literal>, <literal>$TEMP</literal> or <literal>$TMP</literal> are set to.</entry>
+          </row>
+          <row>
+            <entry><literal>%g</literal></entry>
+            <entry>User group</entry>
+            <entry>This is the name of the group running the service manager instance. In case of the system manager this resolves to <literal>root</literal>.</entry>
+          </row>
+          <row>
+            <entry><literal>%G</literal></entry>
+            <entry>User GID</entry>
+            <entry>This is the numeric GID of the user running the service manager instance. In case of the system manager this resolves to <literal>0</literal>.</entry>
+          </row>
+          <row>
+            <entry><literal>%u</literal></entry>
+            <entry>User name</entry>
+            <entry>This is the name of the user running the service manager instance. In case of the system manager this resolves to <literal>root</literal>.</entry>
+          </row>
+          <row>
+            <entry><literal>%U</literal></entry>
+            <entry>User UID</entry>
+            <entry>This is the numeric UID of the user running the service manager instance. In case of the system manager this resolves to <literal>0</literal>.</entry>
+          </row>
+          <row>
+            <entry><literal>%v</literal></entry>
+            <entry>Kernel release</entry>
+            <entry>Identical to <command>uname -r</command> output</entry>
+          </row>
+          <row>
+            <entry><literal>%V</literal></entry>
+            <entry>Directory for larger and persistent temporary files</entry>
+            <entry>This is either <filename>/var/tmp</filename> or the path <literal>$TMPDIR</literal>, <literal>$TEMP</literal> or <literal>$TMP</literal> are set to.</entry>
+          </row>
+          <row>
+            <entry><literal>%%</literal></entry>
+            <entry>Single percent sign</entry>
+            <entry>Use <literal>%%</literal> in place of <literal>%</literal> to specify a single percent sign.</entry>
+          </row>
+        </tbody>
+      </tgroup>
+    </table>
+  </refsect1>
+
+  <refsect1>
+    <title>Examples</title>
+
+    <example>
+      <title>Allowing units to be enabled</title>
+
+      <para>The following snippet (highlighted) allows a unit (e.g.
+      <filename>foo.service</filename>) to be enabled via
+      <command>systemctl enable</command>:</para>
+
+      <programlisting>[Unit]
+Description=Foo
+
+[Service]
+ExecStart=/usr/sbin/foo-daemon
+
+<emphasis>[Install]</emphasis>
+<emphasis>WantedBy=multi-user.target</emphasis></programlisting>
+
+      <para>After running <command>systemctl enable</command>, a
+      symlink
+      <filename>/etc/systemd/system/multi-user.target.wants/foo.service</filename>
+      linking to the actual unit will be created. It tells systemd to
+      pull in the unit when starting
+      <filename>multi-user.target</filename>. The inverse
+      <command>systemctl disable</command> will remove that symlink
+      again.</para>
+    </example>
+
+    <example>
+      <title>Overriding vendor settings</title>
+
+      <para>There are two methods of overriding vendor settings in
+      unit files: copying the unit file from
+      <filename>/usr/lib/systemd/system</filename> to
+      <filename>/etc/systemd/system</filename> and modifying the
+      chosen settings. Alternatively, one can create a directory named
+      <filename><replaceable>unit</replaceable>.d/</filename> within
+      <filename>/etc/systemd/system</filename> and place a drop-in
+      file <filename><replaceable>name</replaceable>.conf</filename>
+      there that only changes the specific settings one is interested
+      in. Note that multiple such drop-in files are read if
+      present, processed in lexicographic order of their filename.</para>
+
+      <para>The advantage of the first method is that one easily
+      overrides the complete unit, the vendor unit is not parsed at
+      all anymore. It has the disadvantage that improvements to the
+      unit file by the vendor are not automatically incorporated on
+      updates.</para>
+
+      <para>The advantage of the second method is that one only
+      overrides the settings one specifically wants, where updates to
+      the unit by the vendor automatically apply. This has the
+      disadvantage that some future updates by the vendor might be
+      incompatible with the local changes.</para>
+
+      <para>This also applies for user instances of systemd, but with
+      different locations for the unit files. See the section on unit
+      load paths for further details.</para>
+
+      <para>Suppose there is a vendor-supplied unit
+      <filename>/usr/lib/systemd/system/httpd.service</filename> with
+      the following contents:</para>
+
+      <programlisting>[Unit]
+Description=Some HTTP server
+After=remote-fs.target sqldb.service
+Requires=sqldb.service
+AssertPathExists=/srv/webserver
+
+[Service]
+Type=notify
+ExecStart=/usr/sbin/some-fancy-httpd-server
+Nice=5
+
+[Install]
+WantedBy=multi-user.target</programlisting>
+
+      <para>Now one wants to change some settings as an administrator:
+      firstly, in the local setup, <filename>/srv/webserver</filename>
+      might not exist, because the HTTP server is configured to use
+      <filename>/srv/www</filename> instead. Secondly, the local
+      configuration makes the HTTP server also depend on a memory
+      cache service, <filename>memcached.service</filename>, that
+      should be pulled in (<varname>Requires=</varname>) and also be
+      ordered appropriately (<varname>After=</varname>). Thirdly, in
+      order to harden the service a bit more, the administrator would
+      like to set the <varname>PrivateTmp=</varname> setting (see
+      <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+      for details). And lastly, the administrator would like to reset
+      the niceness of the service to its default value of 0.</para>
+
+      <para>The first possibility is to copy the unit file to
+      <filename>/etc/systemd/system/httpd.service</filename> and
+      change the chosen settings:</para>
+
+      <programlisting>[Unit]
+Description=Some HTTP server
+After=remote-fs.target sqldb.service <emphasis>memcached.service</emphasis>
+Requires=sqldb.service <emphasis>memcached.service</emphasis>
+AssertPathExists=<emphasis>/srv/www</emphasis>
+
+[Service]
+Type=notify
+ExecStart=/usr/sbin/some-fancy-httpd-server
+<emphasis>Nice=0</emphasis>
+<emphasis>PrivateTmp=yes</emphasis>
+
+[Install]
+WantedBy=multi-user.target</programlisting>
+
+      <para>Alternatively, the administrator could create a drop-in
+      file
+      <filename>/etc/systemd/system/httpd.service.d/local.conf</filename>
+      with the following contents:</para>
+
+      <programlisting>[Unit]
+After=memcached.service
+Requires=memcached.service
+# Reset all assertions and then re-add the condition we want
+AssertPathExists=
+AssertPathExists=/srv/www
+
+[Service]
+Nice=0
+PrivateTmp=yes</programlisting>
+
+      <para>Note that for drop-in files, if one wants to remove
+      entries from a setting that is parsed as a list (and is not a
+      dependency), such as <varname>AssertPathExists=</varname> (or
+      e.g. <varname>ExecStart=</varname> in service units), one needs
+      to first clear the list before re-adding all entries except the
+      one that is to be removed. Dependencies (<varname>After=</varname>, etc.)
+      cannot be reset to an empty list, so dependencies can only be
+      added in drop-ins. If you want to remove dependencies, you have
+      to override the entire unit.</para>
+
+    </example>
+  </refsect1>
+
+  <refsect1>
+    <title>See Also</title>
+    <para>
+      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+      <citerefentry project='man-pages'><refentrytitle>uname</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+
+</refentry>