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.