systemd.timer — Timer unit configuration
timer.timer
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).
Unless DefaultDependencies= is set to
false, all timer units will implicitly have
dependencies of type 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.
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.unit(5).
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 distribute the wake-up time in networked
installations, as well as optimizing 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.
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=.
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.