systemd.timer

SYSTEMD.TIMER(5)                  systemd.timer                 SYSTEMD.TIMER(5)



NAME
       systemd.timer - Timer unit configuration

SYNOPSIS
       timer.timer

DESCRIPTION
       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.

AUTOMATIC DEPENDENCIES
   Implicit Dependencies
       The following dependencies are implicitly added:

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

   Default Dependencies
       The following dependencies are added unless DefaultDependencies=no is
       set:

       •   Timer units will automatically have dependencies of type Requires=
           and After= on sysinit.target, a dependency of type Before= on
           timers.target, as well as Conflicts= and Before= on shutdown.target
           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 DefaultDependencies= option.

       •   Timer units with at least one OnCalendar= directive will have an
           additional After= dependency on time-sync.target to avoid being
           started before the system clock has been correctly set.

OPTIONS
       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=,
       OnUnitInactiveSec=
           Defines monotonic timers relative to different starting points:

           Table 1. Settings and their starting points
           ┌───────────────────┬─────────────────────────────┐
           │Setting            Meaning                     │
           ├───────────────────┼─────────────────────────────┤
           │OnActiveSec=       │ Defines a timer relative to │
           │                   │ the moment the timer unit   │
           │                   │ itself is activated.        │
           ├───────────────────┼─────────────────────────────┤
           │OnBootSec=         │ Defines a timer relative to │
           │                   │ when the machine was booted │
           │                   │ up. In containers, for the  │
           │                   │ system manager instance,    │
           │                   │ this is mapped to           │
           │                   │ OnStartupSec=, making both  │
           │                   │ equivalent.                 │
           ├───────────────────┼─────────────────────────────┤
           │OnStartupSec=      │ Defines a timer relative to │
           │                   │ when the service manager    │
           │                   │ was first started. For      │
           │                   │ system timer units this is  │
           │                   │ very similar to OnBootSec=  │
           │                   │ 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.                │
           ├───────────────────┼─────────────────────────────┤
           │OnUnitActiveSec=   │ Defines a timer relative to │
           │                   │ when the unit the timer     │
           │                   │ unit is activating was last │
           │                   │ activated.                  │
           ├───────────────────┼─────────────────────────────┤
           │OnUnitInactiveSec= │ Defines a timer relative to │
           │                   │ when the unit the timer     │
           │                   │ unit is activating was last │
           │                   │ deactivated.                │
           └───────────────────┴─────────────────────────────┘
           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
           OnBootSec= and OnUnitActiveSec=, 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 OnCalendar=
           calendar expressions may be combined in the same timer unit.

           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 generally pauses, too. Note that if WakeSystem= 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.

           If the empty string is assigned to any of these options, the list of
           timers is reset (both monotonic timers and OnCalendar= timers, see
           below), 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.

       OnCalendar=
           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.

           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.

           If the empty string is assigned to any of these options, the list of
           timers is reset (both OnCalendar= timers and monotonic timers, see
           above), and all prior assignments will have no effect.

       AccuracySec=
           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.

           Note that this setting is primarily a power saving option that allows
           coalescing CPU wake-ups. It should not be confused with
           RandomizedDelaySec= (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.

       RandomizedDelaySec=
           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 FixedRandomDelay=, see below.

           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.

           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, while this setting does the
           opposite: it stretches timer events over an interval, 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 1 minute and RandomizedDelaySec= to 0, thus
           encouraging coalescing of timer events. In order to optimally stretch
           timer events over a certain range of time, set AccuracySec=1us and
           RandomizedDelaySec= to some higher value.

       FixedRandomDelay=
           Takes a boolean argument. When enabled, the randomized offset
           specified by RandomizedDelaySec= 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.

           This setting has no effect if RandomizedDelaySec= is set to 0.
           Defaults to false.

       OnClockChange=, OnTimezoneChange=
           These options take boolean arguments. When true, the service unit
           will be triggered when the system clock (CLOCK_REALTIME) jumps
           relative to the monotonic clock (CLOCK_MONOTONIC), 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 false.

       Unit=
           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.

       Persistent=
           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
           RandomizedDelaySec=. 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 OnCalendar=. Defaults to
           false.

           Use systemctl clean --what=state ...  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 systemctl(1)
           for details.

       WakeSystem=
           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.

           Note that this functionality requires privileges and is thus
           generally only available in the system service manager.

           Note that behaviour of monotonic clock timers (as configured with
           OnActiveSec=, OnBootSec=, OnStartupSec=, OnUnitActiveSec=,
           OnUnitInactiveSec=, see above) is altered depending on this option.
           If false, a monotonic clock is used that is paused during system
           suspend (CLOCK_MONOTONIC), if true a different monotonic clock is
           used that continues advancing during system suspend (CLOCK_BOOTTIME),
           see clock_getres(2) for details.

       RemainAfterElapse=
           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 Unit=, 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 RemainAfterElapse=
           is on, starting the timer a second time has no effect. However, if
           RemainAfterElapse= 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 true.

SEE ALSO
       systemd(1), systemctl(1), systemd.unit(5), systemd.service(5),
       systemd.time(7), systemd.directives(7), systemd-system.conf(5), prctl(2)



systemd 247                                                     SYSTEMD.TIMER(5)