Adding upstream version 252.22.upstream/252.22upstream

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

1 files changed, 398 insertions, 0 deletions

diff --git a/man/systemd.timer.xml b/man/systemd.timer.xml
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+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="systemd.timer" xmlns:xi="http://www.w3.org/2001/XInclude">
+  <refentryinfo>
+    <title>systemd.timer</title>
+    <productname>systemd</productname>
+  </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>Note that in case the unit to activate is already active at the time the timer elapses it is not restarted,
+    but simply left running. There is no concept of spawning new service instances in this case. Due to this, services
+    with <varname>RemainAfterExit=</varname> set (which stay around continuously even after the service's main process
+    exited) are usually not suitable for activation via repetitive timers, as they will only be activated once, and
+    then stay around forever.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Automatic Dependencies</title>
+
+    <refsect2>
+      <title>Implicit Dependencies</title>
+
+      <para>The following dependencies are implicitly added:</para>
+
+      <itemizedlist>
+        <listitem><para>Timer units automatically gain a <varname>Before=</varname>
+        dependency on the service they are 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>Timer units will automatically have dependencies of type <varname>Requires=</varname> and
+        <varname>After=</varname> on <filename>sysinit.target</filename>, a dependency of type <varname>Before=</varname>
+        on <filename>timers.target</filename>, as well as <varname>Conflicts=</varname> and <varname>Before=</varname> on
+        <filename>shutdown.target</filename> to ensure that they are stopped cleanly prior to system shutdown. Only timer
+        units involved with early boot or late system shutdown should disable the
+        <varname>DefaultDependencies=</varname> option.</para></listitem>
+
+        <listitem><para>Timer units with at least one <varname>OnCalendar=</varname> directive acquire a pair
+        of additional <varname>After=</varname> dependencies on <filename>time-set.target</filename> and
+        <filename>time-sync.target</filename>, in order to avoid being started before the system clock has
+        been correctly set. See
+        <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+        for details on these two targets.</para></listitem>
+      </itemizedlist>
+    </refsect2>
+  </refsect1>
+
+  <refsect1>
+    <title>Options</title>
+
+    <para>Timer unit files may include [Unit] and [Install] sections, which are described in
+    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+    </para>
+
+    <para>Timer unit 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:</para>
+
+        <table>
+          <title>Settings and their starting points</title>
+
+          <tgroup cols='2'>
+            <thead>
+              <row>
+                <entry>Setting</entry>
+                <entry>Meaning</entry>
+              </row>
+            </thead>
+            <tbody>
+              <row>
+                <entry><varname>OnActiveSec=</varname></entry>
+                <entry>Defines a timer relative to the moment the timer unit itself is activated.</entry>
+              </row>
+              <row>
+                <entry><varname>OnBootSec=</varname></entry>
+                <entry>Defines a timer relative to when the machine was booted up. In containers, for the system manager instance, this is mapped to <varname>OnStartupSec=</varname>, making both equivalent.</entry>
+              </row>
+              <row>
+                <entry><varname>OnStartupSec=</varname></entry>
+                <entry>Defines a timer relative to when the service manager was first started. For system timer units this is very similar to <varname>OnBootSec=</varname> as the system service manager is generally started very early at boot. It's primarily useful when configured in units running in the per-user service manager, as the user service manager is generally started on first login only, not already during boot.</entry>
+              </row>
+              <row>
+                <entry><varname>OnUnitActiveSec=</varname></entry>
+                <entry>Defines a timer relative to when the unit the timer unit is activating was last activated.</entry>
+              </row>
+              <row>
+                <entry><varname>OnUnitInactiveSec=</varname></entry>
+                <entry>Defines a timer relative to when the unit the timer unit is activating was last deactivated.</entry>
+              </row>
+            </tbody>
+          </tgroup>
+        </table>
+
+        <para>Multiple directives may be combined of the same and of different types, in which case the timer
+        unit will trigger whenever any of the specified timer expressions elapse. 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. Moreover, both
+        monotonic time expressions and <varname>OnCalendar=</varname> calendar expressions may be combined in
+        the same timer unit.</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.time</refentrytitle><manvolnum>7</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 generally pauses, too. Note that if
+        <varname>WakeSystem=</varname> is used, a different monotonic clock is selected that continues to
+        advance while the system is suspended and thus can be used as the trigger to resume the
+        system.</para>
+
+        <para>If the empty string is assigned to any of these options, the list of timers is reset (both
+        monotonic timers and <varname>OnCalendar=</varname> timers, see below), 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>
+
+        <para>May be specified more than once, in which case the timer unit will trigger whenever any of the
+        specified expressions elapse. Moreover calendar timers and monotonic timers (see above) may be
+        combined within the same timer unit.</para>
+
+        <para>If the empty string is assigned to any of these options, the list of timers is reset (both
+        <varname>OnCalendar=</varname> timers and monotonic timers, see above), and all prior assignments
+        will have no effect.</para>
+
+        <para>Note that calendar timers might be triggered at unexpected times if the system's realtime clock
+        is not set correctly. Specifically, on systems that lack a battery-buffered Realtime Clock (RTC) it
+        might be wise to enable <filename>systemd-time-wait-sync.service</filename> to ensure the clock is
+        adjusted to a network time source <emphasis>before</emphasis> the timer event is set up. Timer units
+        with at least one <varname>OnCalendar=</varname> expression are automatically ordered after
+        <filename>time-sync.target</filename>, which <filename>systemd-time-wait-sync.service</filename> is
+        ordered before.</para>
+
+        <para>When a system is temporarily put to sleep (i.e. system suspend or hibernation) the realtime
+        clock does not pause. When a calendar timer elapses while the system is sleeping it will not be acted
+        on immediately, but once the system is later resumed it will catch up and process all timers that
+        triggered while the system was sleeping. Note that if a calendar timer elapsed more than once while
+        the system was continously sleeping the timer will only result in a single service activation. If
+        <varname>WakeSystem=</varname> (see below) is enabled a calendar time event elapsing while the system
+        is suspended will cause the system to wake up (under the condition the system's hardware supports
+        time-triggered wake-up functionality).</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 optimize 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>
+
+        <para>Note that this setting is primarily a power saving option that allows coalescing CPU
+        wake-ups. It should not be confused with <varname>RandomizedDelaySec=</varname> (see below) which
+        adds a random value to the time the timer shall elapse next and whose purpose is the opposite: to
+        stretch elapsing of timer events over a longer period to reduce workload spikes. For further details
+        and explanations and how both settings play together, see below.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>RandomizedDelaySec=</varname></term>
+
+        <listitem><para>Delay the timer by a randomly selected, evenly distributed amount of time between 0
+        and the specified time value. Defaults to 0, indicating that no randomized delay shall be applied.
+        Each timer unit will determine this delay randomly before each iteration, and the delay will simply
+        be added on top of the next determined elapsing time, unless modified with
+        <varname>FixedRandomDelay=</varname>, see below.</para>
+
+        <para>This setting is useful to stretch dispatching of similarly configured timer events over a
+        certain time interval, to prevent them from firing all at the same time, possibly resulting in
+        resource congestion.</para>
+
+        <para>Note the relation to <varname>AccuracySec=</varname> above: the latter allows the service
+        manager to coalesce timer events within a specified time range in order to minimize wakeups, while
+        this setting does the opposite: it stretches timer events over an interval, to make it unlikely that
+        they fire simultaneously. If <varname>RandomizedDelaySec=</varname> and
+        <varname>AccuracySec=</varname> are used in conjunction, first the randomized delay is added, and
+        then the result is possibly further shifted to coalesce it with other timer events happening on the
+        system. As mentioned above <varname>AccuracySec=</varname> defaults to 1 minute and
+        <varname>RandomizedDelaySec=</varname> to 0, thus encouraging coalescing of timer events. In order to
+        optimally stretch timer events over a certain range of time, set
+        <varname>AccuracySec=1us</varname> and <varname>RandomizedDelaySec=</varname> to some higher value.
+        </para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>FixedRandomDelay=</varname></term>
+
+        <listitem><para>Takes a boolean argument. When enabled, the randomized offset specified by
+        <varname>RandomizedDelaySec=</varname> is reused for all firings of the same timer. For a given timer
+        unit, the offset depends on the machine ID, user identifier and timer name, which means that it is
+        stable between restarts of the manager. This effectively creates a fixed offset for an individual
+        timer, reducing the jitter in firings of this timer, while still avoiding firing at the same time as
+        other similarly configured timers.</para>
+
+        <para>This setting has no effect if <varname>RandomizedDelaySec=</varname> is set to 0. Defaults to
+        <option>false</option>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>OnClockChange=</varname></term>
+        <term><varname>OnTimezoneChange=</varname></term>
+
+        <listitem><para>These options take boolean arguments. When true, the service unit will be triggered
+        when the system clock (<constant>CLOCK_REALTIME</constant>) jumps relative to the monotonic clock
+        (<constant>CLOCK_MONOTONIC</constant>), or when the local system timezone is modified. These options
+        can be used alone or in combination with other timer expressions (see above) within the same timer
+        unit. These options default to <option>false</option>.</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. Such triggering
+        is nonetheless subject to the delay imposed by <varname>RandomizedDelaySec=</varname>.
+        This is useful to catch up on missed runs of the service when the system was powered down. Note that
+        this setting only has an effect on timers configured with <varname>OnCalendar=</varname>. Defaults to
+        <option>false</option>.</para>
+
+        <para>Use <command>systemctl clean --what=state …</command> on the timer unit to remove the timestamp
+        file maintained by this option from disk. In particular, use this command before uninstalling a timer
+        unit. See
+        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> for
+        details.</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
+        <option>false</option>.</para>
+
+        <para>Note that this functionality requires privileges and is thus generally only available in the
+        system service manager.</para>
+
+        <para>Note that behaviour of monotonic clock timers (as configured with
+        <varname>OnActiveSec=</varname>, <varname>OnBootSec=</varname>, <varname>OnStartupSec=</varname>,
+        <varname>OnUnitActiveSec=</varname>, <varname>OnUnitInactiveSec=</varname>, see above) is altered
+        depending on this option. If false, a monotonic clock is used that is paused during system suspend
+        (<constant>CLOCK_MONOTONIC</constant>), if true a different monotonic clock is used that continues
+        advancing during system suspend (<constant>CLOCK_BOOTTIME</constant>), see
+        <citerefentry><refentrytitle>clock_getres</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
+        details.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>RemainAfterElapse=</varname></term>
+
+        <listitem><para>Takes a boolean argument. If true, a timer will stay loaded, and its state remains
+        queryable even after it elapsed and the associated unit (as configured with <varname>Unit=</varname>,
+        see above) deactivated again. If false, an elapsed timer unit that cannot elapse anymore is unloaded
+        once its associated unit deactivated again. Turning this off is particularly useful for transient
+        timer units. Note that this setting has an effect when repeatedly starting a timer unit: if
+        <varname>RemainAfterElapse=</varname> is on, starting the timer a second time has no effect. However,
+        if <varname>RemainAfterElapse=</varname> is off and the timer unit was already unloaded, it can be
+        started again, and thus the service can be triggered multiple times. Defaults to
+        <option>true</option>.</para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <xi:include href="systemd.service.xml" xpointer="shared-unit-options" />
+  </refsect1>
+
+  <refsect1>
+      <title>See Also</title>
+      <para>Environment variables with details on the trigger will be set for triggered units. See the
+      <literal>Environment Variables Set on Triggered Units</literal> section in
+      <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+      for more details.</para>
+      <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>