systemd-stable/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>, timer units will
                implicitly have dependencies of type
                <varname>Conflicts=</varname> and
                <varname>Before=</varname> on
                <filename>shutdown.target</filename>. These ensure
                that timer units are stopped cleanly prior to system
                shutdown. Only timer units involved with early boot or
                late system shutdown should disable this
                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>
                </variablelist>
        </refsect1>

        <refsect1>
                  <title>See Also</title>
                  <para>
                          <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</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>