systemd.timer - Timer unit configuration




   A unit configuration file whose name ends in ".timer" encodes
   information about a timer controlled and supervised by systemd, for
   timer-based activation.

   This man page lists the configuration options specific to this unit
   type. See systemd.unit(5) 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.

   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 foo.timer activates a matching service foo.service. The unit
   to activate may be controlled by Unit= (see below).

   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 RemainAfterExit= 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.


   Timer units automatically gain a Before= dependency on the service they
   are supposed to activate.

   Unless DefaultDependencies= in the "[Unit]" section is set to false,
   all timer units will implicitly have dependencies of type Requires= and
   After= on, a dependency of type Before= on, as well as Conflicts= and Before= on to
   ensure that they are stopped cleanly prior to system shutdown. Timer
   units with at least one OnCalendar= directive will have an additional
   After= dependency on 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
   DefaultDependencies= option.


   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:

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

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

       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 systemd.time(7).

       If a timer configured with OnBootSec= or OnStartupSec= 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.

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

       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.

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

       Defines realtime (i.e. wallclock) timers with calendar event
       expressions. See systemd.time(7) for more information on the syntax
       of calendar event expressions. Otherwise, the semantics are similar
       to OnActiveSec= and related settings.

       Note that timers do not necessarily expire at the precise time
       configured with this setting, as it is subject to the AccuracySec=
       setting below.

       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 OnCalendar=, OnActiveSec=, OnBootSec=,
       OnStartupSec=, OnUnitActiveSec= or OnUnitInactiveSec= and ending
       the time configured with AccuracySec= 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 systemd-system.conf(5)'s
       TimerSlackNSec= setting. See prctl(2) for details. To optimize
       power consumption, make sure to set this value as high as possible
       and as low as necessary.

       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 each time it is started,
       and the delay will simply be added on top of the next determined
       elapsing time. This is useful to stretch dispatching of similarly
       configured timer events over a certain amount time, to avoid that
       they all fire at the same time, possibly resulting in resource
       congestion. Note the relation to AccuracySec= above: the latter
       allows the service manager to coalesce timer events within a
       specified time range in order to minimize wakeups, the former does
       the opposite: it stretches timer events over a time range, to make
       it unlikely that they fire simultaneously. If RandomizedDelaySec=
       and AccuracySec= 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 AccuracySec= defaults to 1min and
       RandomizedDelaySec= to 0, thus encouraging coalescing of timer
       events. In order to optimally stretch timer events over a certain
       range of time, make sure to set RandomizedDelaySec= to a higher
       value, and AccuracySec=1us.

       The unit to activate when this timer elapses. The argument is a
       unit name, whose suffix is not ".timer". 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.

       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 OnCalendar=. Defaults to false.

       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 false.

       Takes a boolean argument. If true, an elapsed timer will stay
       loaded, and its state remains queriable. If false, an elapsed timer
       unit that cannot elapse anymore is unloaded. Turning this off is
       particularly useful for transient timer units that shall disappear
       after they first elapse. Note that this setting has an effect on
       repeatedly starting a timer unit that only elapses once: if
       RemainAfterElapse= is on, it will not be started again, and is
       guaranteed to elapse only once. However, if RemainAfterElapse= is
       off, it might be started again if it is already elapsed, and thus
       be triggered multiple times. Defaults to yes.


   systemd(1), systemctl(1), systemd.unit(5), systemd.service(5),
   systemd.time(7), systemd.directives(7), systemd-system.conf(5),


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