# systemd.timer

## 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=yes_ 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 _StopWhenUnneeded=yes_ 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.
    


## 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 acquire a
               pair of additional _After=_ dependencies on time-set.target and
               time-sync.target, in order to avoid being started before the
               system clock has been correctly set. See systemd.special(7)
               for details on these two targets.
    


## OPTIONS



           Timer unit files may include [Unit] and [Install] sections, which
           are described in systemd.unit(5).
    
           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:
    
           _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.
    
               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
               systemd-time-wait-sync.service to ensure the clock is adjusted
               to a network time source _before_ the timer event is set up.
               Timer units with at least one _OnCalendar=_ expression are
               automatically ordered after time-sync.target, which
               systemd-time-wait-sync.service is ordered before.
    
               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 _WakeSystem=_ (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).
    
               Added in version 197.
    
           _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.
    
               Added in version 209.
    
           _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, unless modified with _FixedRandomDelay=_ ,
               see below. The delay is added on top of the next determined
               elapsing time or the service manager's startup time, whichever
               is later.
    
               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 on the local system.
    
               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.
    
               Added in version 229.
    
           _FixedRandomDelay=_
               Takes a boolean argument. When enabled, the randomized delay
               specified by _RandomizedDelaySec=_ is chosen deterministically,
               and remains stable between all firings of the same timer, even
               if the manager is restarted. The delay is derived from the
               machine ID, the manager's user identifier, and the timer
               unit's name. This effectively creates a unique fixed offset
               for each timer, reducing the jitter in firings of an
               individual timer while still avoiding firing at the same time
               as other similarly configured timers.
    
               This setting has an effect only if _RandomizedDelaySec=_ is not
               0. Defaults to **false**.
    
               Added in version 247.
    
           _RandomizedOffsetSec=_
               Offsets the timer by a stable, randomly-selected, and evenly
               distributed amount of time between 0 and the specified time
               value. Defaults to 0, indicating that no such offset shall be
               applied. The offset is chosen deterministically, and is
               derived the same way as _FixedRandomDelay=_ , see above. The
               offset is added on top of the next determined elapsing time.
               This setting only has an effect on timers configured with
               _OnCalendar=_ , and it can be combined with _RandomizedDelaySec=_.
    
               Much like _RandomizedDelaySec=_ , this setting is for
               distributing timer events to prevent them from firing all at
               once. However, this setting is most useful to prevent resource
               congestion on a remote service, from a fleet of
               similarly-configured clients. Unlike _RandomizedDelaySec=_ , this
               setting applies its offset with no regard to manager startup
               time. This maintains the periodicity of configured _OnCalendar=_
               events across manager restarts.
    
               For example, let's say you're running a backup service and
               have a fleet of laptops that wish to make backups weekly. To
               distribute load on the backup service, each laptop should
               randomly pick a weekday to upload its backups. This could be
               achieved by setting _OnCalendar=_ to "weekly", and then
               configuring a _RandomizedDelaySec=_ of "5 days" with
               _FixedRandomDelay=_ enabled. Let's say that some laptop randomly
               chooses a delay of 4 days. If this laptop is restarted more
               often than that, then the timer will never fire: on each fresh
               boot, the 4 day delay is restarted and will not be finished by
               the time of the next shutdown. Instead, you should use
               _RandomizedOffsetSec=_ , which will maintain the configured
               weekly cadence of timer events, even across reboots.
    
               Added in version 258.
    
           _DeferReactivation=_
               Takes a boolean argument. When enabled, the timer schedules
               the next elapse based on the trigger unit entering inactivity,
               instead of the last trigger time. This is most apparent in the
               case where the service unit takes longer to run than the timer
               interval. With this setting enabled, the timer will schedule
               the next elapse based on when the service finishes running,
               and so it will have to wait until the next realtime elapse
               time to trigger. Otherwise, the default behavior is for the
               timer unit to immediately trigger again once the service
               finishes running. This happens because the timer schedules the
               next elapse based on the previous trigger time, and since the
               interval is shorter than the service runtime, that elapse will
               be in the past, causing it to immediately trigger once done.
    
               This setting has an effect only if a realtime timer has been
               specified with _OnCalendar=_. Defaults to **false**.
    
               Added in version 257.
    
           _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**.
    
               Added in version 242.
    
           _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.
    
               Added in version 212.
    
           _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.
    
               Added in version 212.
    
           _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**.
    
               Added in version 229.
    
           Check systemd.unit(5), systemd.exec(5), and systemd.kill(5) for
           more settings.
    


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