NAME | SYNOPSIS | DESCRIPTION | AUTOMATIC DEPENDENCIES | OPTIONS | SEE ALSO | COLOPHON

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

NAME         top

       systemd.timer - Timer unit configuration

SYNOPSIS         top

       timer.timer

DESCRIPTION         top

       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         top

       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 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.
       Timer units with at least one OnCalendar= directive will have an
       additional After= dependency on timer-sync.target 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.

OPTIONS         top

       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:
           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.

       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.

       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.

       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 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.

       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. 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.

       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.

       RemainAfterElapse=
           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.

SEE ALSO         top

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

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have a bug
       report for this manual page, see 
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.  This
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       COLOPHON (which is not part of the original manual page), send a mail
       to man-pages@man7.org

systemd 233                                                 SYSTEMD.TIMER(5)