SYSTEMD.TIMER(5)



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:

       o   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:

       o   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.

       o   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. 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.

       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. 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, an elapsed timer will stay
           loaded, and its state remains queryable. 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)

systemd 245                                                   SYSTEMD.TIMER(5)

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