mirror of
https://github.com/systemd/systemd.git
synced 2024-12-22 17:35:35 +03:00
417 lines
23 KiB
XML
417 lines
23 KiB
XML
<?xml version='1.0'?>
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.5/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=yes</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. Target units, which by default do not deactivate on their own, can be
|
|
activated repeatedly by timers by setting <varname>StopWhenUnneeded=yes</varname> on them. This will cause a
|
|
target unit to be stopped immediately after its activation, if it is not a dependency of another running unit.</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 continuously 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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v197"/></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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v209"/></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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v229"/></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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v247"/></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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v242"/></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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v212"/></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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v212"/></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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v229"/></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 or Propagated by the Service Manager</literal> section in
|
|
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
for more details.</para>
|
|
<para><simplelist type="inline">
|
|
<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>
|
|
</simplelist></para>
|
|
</refsect1>
|
|
|
|
</refentry>
|