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.

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: 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.

           May be specified more than once.

       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

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