A unit configuration file whose name ends in ".timer" encodes
information about a timer controlled and supervised by systemd, for
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.
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=,
Defines monotonic timers relative to different starting
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.
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
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.
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
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=
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 OnCalendar=
and ending the time configured with
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)
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.
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
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.
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.
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.
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.