man/systemd.path.xml

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<refentry id="systemd.path">
  <refentryinfo>
    <title>systemd.path</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Lennart</firstname>
        <surname>Poettering</surname>
        <email>lennart@poettering.net</email>
      </author>
    </authorgroup>
  </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>
  </refsect1>

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

    <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>

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

    <para>Unless <varname>DefaultDependencies=false</varname> is used,
    path units will implicitly 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
    this option.
    </para>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>Path files must include a [Path] section, which carries
    information about the path(s) 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>
    </variablelist>
  </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>