systemd/man/systemd.timer.xml

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<refentry id="systemd.timer">
  <refentryinfo>
    <title>systemd.timer</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.timer</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd.timer</refname>
    <refpurpose>Timer unit configuration</refpurpose>
  </refnamediv>

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

  <refsect1>
    <title>Description</title>

    <para>A unit configuration file whose name ends in
    <literal>.timer</literal> encodes information about a timer
    controlled and supervised by systemd, for timer-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 timer specific configuration options are
    configured in the [Timer] section.</para>

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

    <para>Unless <varname>DefaultDependencies=</varname> is set to
    <option>false</option>, all timer units will implicitly have
    dependencies of type <varname>Conflicts=</varname> and
    <varname>Before=</varname> on <filename>shutdown.target</filename>
    to ensure that they are stopped cleanly prior to system shutdown.
    Timer units with at least one <varname>OnCalendar=</varname>
    directive will have an additional <varname>After=</varname>
    dependency on <filename>timer-sync.target</filename> to avoid
    being started before the system clock has been correctly set. Only
    timer units involved with early boot or late system shutdown
    should disable the <varname>DefaultDependencies=</varname>
    option.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>Timer files must include a [Timer] section, which carries
    information about the timer it defines. The options specific to
    the [Timer] section of timer units are the following:</para>

    <variablelist class='unit-directives'>
      <varlistentry>
        <term><varname>OnActiveSec=</varname></term>
        <term><varname>OnBootSec=</varname></term>
        <term><varname>OnStartupSec=</varname></term>
        <term><varname>OnUnitActiveSec=</varname></term>
        <term><varname>OnUnitInactiveSec=</varname></term>

        <listitem><para>Defines monotonic timers relative to different
        starting points: <varname>OnActiveSec=</varname> defines a
        timer relative to the moment the timer itself is activated.
        <varname>OnBootSec=</varname> defines a timer relative to when
        the machine was booted up. <varname>OnStartupSec=</varname>
        defines a timer relative to when systemd was first started.
        <varname>OnUnitActiveSec=</varname> defines a timer relative
        to when the unit the timer is activating was last activated.
        <varname>OnUnitInactiveSec=</varname> defines a timer relative
        to when the unit the timer is activating was last
        deactivated.</para>

        <para>Multiple directives may be combined of the same and of
        different types. For example, by combining
        <varname>OnBootSec=</varname> and
        <varname>OnUnitActiveSec=</varname>, it is possible to define
        a timer that elapses in regular intervals and activates a
        specific service each time.</para>

        <para>The arguments to the directives are time spans
        configured in seconds. Example: "OnBootSec=50" means 50s after
        boot-up. The argument may also include time units. Example:
        "OnBootSec=5h 30min" means 5 hours and 30 minutes after
        boot-up. For details about the syntax of time spans, see
        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

        <para>If a timer configured with <varname>OnBootSec=</varname>
        or <varname>OnStartupSec=</varname> is already in the past
        when the timer unit is activated, it will immediately elapse
        and the configured unit is started. This is not the case for
        timers defined in the other directives.</para>

        <para>These are monotonic timers, independent of wall-clock
        time and timezones. If the computer is temporarily suspended,
        the monotonic clock stops too.</para>

        <para>If the empty string is assigned to any of these options,
        the list of timers is reset, and all prior assignments will
        have no effect.</para>

        <para>Note that timers do not necessarily expire at the
        precise time configured with these settings, as they are
        subject to the <varname>AccuracySec=</varname> setting
        below.</para></listitem>

      </varlistentry>

      <varlistentry>
        <term><varname>OnCalendar=</varname></term>

        <listitem><para>Defines realtime (i.e. wallclock) timers with
        calendar event expressions. See
        <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
        for more information on the syntax of calendar event
        expressions. Otherwise, the semantics are similar to
        <varname>OnActiveSec=</varname> and related settings.</para>

        <para>Note that timers do not necessarily expire at the
        precise time configured with this setting, as it is subject to
        the <varname>AccuracySec=</varname> setting
        below.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>AccuracySec=</varname></term>

        <listitem><para>Specify the accuracy the timer shall elapse
        with. Defaults to 1min. The timer is scheduled to elapse
        within a time window starting with the time specified in
        <varname>OnCalendar=</varname>,
        <varname>OnActiveSec=</varname>,
        <varname>OnBootSec=</varname>,
        <varname>OnStartupSec=</varname>,
        <varname>OnUnitActiveSec=</varname> or
        <varname>OnUnitInactiveSec=</varname> and ending the time
        configured with <varname>AccuracySec=</varname> later. Within
        this time window, the expiry time will be placed at a
        host-specific, randomized but stable position that is
        synchronized between all local timer units. This is done in
        order to distribute the wake-up time in networked
        installations, as well as optimizing power consumption to
        suppress unnecessary CPU wake-ups. To get best accuracy, set
        this option to 1us. Note that the timer is still subject to
        the timer slack configured via
        <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
        <varname>TimerSlackNSec=</varname> setting. See
        <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        for details. To optimize power consumption, make sure to set
        this value as high as possible and as low as
        necessary.</para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>Unit=</varname></term>

        <listitem><para>The unit to activate when this timer elapses.
        The argument is a unit name, whose suffix is not
        <literal>.timer</literal>. If not specified, this value
        defaults to a service that has the same name as the timer
        unit, except for the suffix. (See above.) It is recommended
        that the unit name that is activated and the unit name of the
        timer unit are named identically, except for the
        suffix.</para></listitem>
      </varlistentry>


      <varlistentry>
        <term><varname>Persistent=</varname></term>

        <listitem><para>Takes a boolean argument. If true, the time
        when the service unit was last triggered is stored on disk.
        When the timer is activated, the service unit is triggered
        immediately if it would have been triggered at least once
        during the time when the timer was inactive. This is useful to
        catch up on missed runs of the service when the machine was
        off. Note that this setting only has an effect on timers
        configured with <varname>OnCalendar=</varname>.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>WakeSystem=</varname></term>

        <listitem><para>Takes a boolean argument. If true, an elapsing
        timer will cause the system to resume from suspend, should it
        be suspended and if the system supports this. Note that this
        option will only make sure the system resumes on the
        appropriate times, it will not take care of suspending it
        again after any work that is to be done is finished. Defaults
        to <varname>false</varname>.</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><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
      </para>
  </refsect1>

</refentry>