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, timer units will
                implicitly have dependencies of type
                Conflicts= and
                Before= on
                shutdown.target. These ensure
                that timer units are stopped cleanly prior to system
                shutdown. Only timer units involved with early boot or
                late system shutdown should disable this
                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.
OnCalendar=¶Defines realtime
                                (i.e. wallclock) timers via 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.
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.