NAME¶systemd.timer - Timer unit configuration
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¶Timer units automatically gain a Before= dependency on the service they are supposed to activate.
Unless DefaultDependencies= in the "[Unit]" section is set to false, all timer units will implicitly 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. 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.
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=
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 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.
Note that timers do not necessarily expire at the precise time configured with this setting, as it is subject to the AccuracySec= setting below.
SEE ALSO¶systemd(1), systemctl(1), systemd.unit(5), systemd.service(5), systemd.time(7), systemd.directives(7), systemd-system.conf(5), prctl(2)