systemd.timer — Timer unit configuration
A unit configuration file whose name ends in
.timer" encodes information about a timer
controlled and supervised by systemd, for timer-based
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
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
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.
The following dependencies are implicitly added:
Timer units automatically gain a
dependency on the service they are supposed to activate.
The following dependencies are added unless
DefaultDependencies=no is set:
Timer units will automatically have dependencies of type
sysinit.target, a dependency of type
timers.target, as well as
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
with at least one
OnCalendar= directive will have an additional
time-sync.target to avoid being started before the system clock has been
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:
Defines monotonic timers relative to different
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.
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
Multiple directives may be combined of the same and of
different types. For example, by combining
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
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
Defines realtime (i.e. wallclock) timers with
calendar event expressions. See
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
May be specified more than once.
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
OnUnitInactiveSec= and ending the time
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
TimerSlackNSec= setting. See
for details. To optimize power consumption, make sure to set
this value as high as possible and as low as
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
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
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
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
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
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,
RemainAfterElapse= is off, it might be
started again if it is already elapsed, and thus be triggered
multiple times. Defaults to