systemd/man/systemd.path.xml

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<refentry id="systemd.path" xmlns:xi="http://www.w3.org/2001/XInclude">
  <refentryinfo>
    <title>systemd.path</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd.path</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd.path</refname>
    <refpurpose>Path unit configuration</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename><replaceable>path</replaceable>.path</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>A unit configuration file whose name ends in
    <literal>.path</literal> encodes information about a path
    monitored by systemd, for path-based activation.</para>

    <para>This man page lists the configuration options specific to
    this unit type. See
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for the common options of all unit configuration files. The common
    configuration items are configured in the generic [Unit] and
    [Install] sections. The path specific configuration options are
    configured in the [Path] section.</para>

    <para>For each path file, a matching unit file must exist,
    describing the unit to activate when the path changes. By default,
    a service by the same name as the path (except for the suffix) is
    activated. Example: a path file <filename>foo.path</filename>
    activates a matching service <filename>foo.service</filename>. The
    unit to activate may be controlled by <varname>Unit=</varname>
    (see below).</para>

    <para>Internally, path units use the
    <citerefentry project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry>
    API to monitor file systems. Due to that, it suffers by the same
    limitations as inotify, and for example cannot be used to monitor
    files or directories changed by other machines on remote NFS file
    systems.</para>

    <para>When a service unit triggered by a path unit terminates (regardless whether it exited successfully
    or failed), monitored paths are checked immediately again, and the service accordingly restarted
    instantly. As protection against busy looping in this trigger/start cycle, a start rate limit is enforced
    on the service unit, see <varname>StartLimitIntervalSec=</varname> and
    <varname>StartLimitBurst=</varname> in
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Unlike
    other service failures, the error condition that the start rate limit is hit is propagated from the
    service unit to the path unit and causes the path unit to fail as well, thus ending the loop.</para>
  </refsect1>

  <refsect1>
    <title>Automatic Dependencies</title>

    <refsect2>
      <title>Implicit Dependencies</title>

      <para>The following dependencies are implicitly added:</para>

      <itemizedlist>
        <listitem><para>If a path unit is beneath another mount unit in the file
        system hierarchy, both a requirement and an ordering dependency
        between both units are created automatically.</para></listitem>

        <listitem><para>An implicit <varname>Before=</varname> dependency is added
        between a path unit and the unit it is supposed to activate.</para></listitem>
      </itemizedlist>
    </refsect2>

    <refsect2>
      <title>Default Dependencies</title>

      <para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para>

      <itemizedlist>
        <listitem><para>Path units will automatically have dependencies of type <varname>Before=</varname> on
        <filename>paths.target</filename>,
        dependencies of type <varname>After=</varname> and <varname>Requires=</varname> on
        <filename>sysinit.target</filename>, and have dependencies of type <varname>Conflicts=</varname> and
        <varname>Before=</varname> on <filename>shutdown.target</filename>. These ensure that path units are terminated
        cleanly prior to system shutdown. Only path units involved with early boot or late system shutdown should
        disable <varname>DefaultDependencies=</varname> option.</para></listitem>
      </itemizedlist>

      <para></para>
    </refsect2>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>Path unit files may include [Unit] and [Install] sections, which are described in
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    </para>

    <para>Path unit files must include a [Path] section, which carries information about the path or paths it
    monitors. The options specific to the [Path] section of path units are the following:</para>

    <variablelist class='unit-directives'>
      <varlistentry>
        <term><varname>PathExists=</varname></term>
        <term><varname>PathExistsGlob=</varname></term>
        <term><varname>PathChanged=</varname></term>
        <term><varname>PathModified=</varname></term>
        <term><varname>DirectoryNotEmpty=</varname></term>

        <listitem><para>Defines paths to monitor for certain changes:
        <varname>PathExists=</varname> may be used to watch the mere
        existence of a file or directory. If the file specified
        exists, the configured unit is activated.
        <varname>PathExistsGlob=</varname> works similar, but checks
        for the existence of at least one file matching the globbing
        pattern specified. <varname>PathChanged=</varname> may be used
        to watch a file or directory and activate the configured unit
        whenever it changes. It is not activated on every write to the
        watched file but it is activated if the file which was open
        for writing gets closed. <varname>PathModified=</varname> is
        similar, but additionally it is activated also on simple
        writes to the watched file.
        <varname>DirectoryNotEmpty=</varname> may be used to watch a
        directory and activate the configured unit whenever it
        contains at least one file.</para>

        <para>The arguments of these directives must be absolute file
        system paths.</para>

        <para>Multiple directives may be combined, of the same and of
        different types, to watch multiple paths. If the empty string
        is assigned to any of these options, the list of paths to
        watch is reset, and any prior assignments of these options
        will not have any effect.</para>

        <para>If a path already exists (in case of
        <varname>PathExists=</varname> and
        <varname>PathExistsGlob=</varname>) or a directory already is
        not empty (in case of <varname>DirectoryNotEmpty=</varname>)
        at the time the path unit is activated, then the configured
        unit is immediately activated as well. Something similar does
        not apply to <varname>PathChanged=</varname> and
        <varname>PathModified=</varname>.</para>

        <para>If the path itself or any of the containing directories
        are not accessible, <command>systemd</command> will watch for
        permission changes and notice that conditions are satisfied
        when permissions allow that. </para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>Unit=</varname></term>

        <listitem><para>The unit to activate when any of the
        configured paths changes. The argument is a unit name, whose
        suffix is not <literal>.path</literal>. If not specified, this
        value defaults to a service that has the same name as the path
        unit, except for the suffix. (See above.) It is recommended
        that the unit name that is activated and the unit name of the
        path unit are named identical, except for the
        suffix.</para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>MakeDirectory=</varname></term>

        <listitem><para>Takes a boolean argument. If true, the
        directories to watch are created before watching. This option
        is ignored for <varname>PathExists=</varname> settings.
        Defaults to <option>false</option>.</para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>DirectoryMode=</varname></term>

        <listitem><para>If <varname>MakeDirectory=</varname> is
        enabled, use the mode specified here to create the directories
        in question. Takes an access mode in octal notation. Defaults
        to <option>0755</option>.</para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>TriggerLimitIntervalSec=</varname></term>
        <term><varname>TriggerLimitBurst=</varname></term>

        <listitem><para>Configures a limit on how often this path unit may be activated within a specific
        time interval. The <varname>TriggerLimitIntervalSec=</varname> may be used to configure the length of
        the time interval in the usual time units <literal>us</literal>, <literal>ms</literal>,
        <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, … and defaults to 2s. See
        <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
        details on the various time units understood. The <varname>TriggerLimitBurst=</varname> setting takes
        a positive integer value and specifies the number of permitted activations per time interval, and
        defaults to 200. Set either to 0 to disable any form of trigger rate limiting. If the limit is hit,
        the unit is placed into a failure mode, and will not watch the path(s) anymore until restarted. Note
        that this limit is enforced before the service activation is enqueued.</para></listitem>
      </varlistentry>
    </variablelist>

    <xi:include href="systemd.service.xml" xpointer="shared-unit-options" />
  </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.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
      </para>
  </refsect1>

</refentry>