diff --git a/man/systemd.timer.xml b/man/systemd.timer.xml index 80dbd641015..b0aa5930f01 100644 --- a/man/systemd.timer.xml +++ b/man/systemd.timer.xml @@ -187,17 +187,13 @@ OnCalendar= - Defines realtime (i.e. wallclock) timers with - calendar event expressions. See - systemd.time7 - for more information on the syntax of calendar event - expressions. Otherwise, the semantics are similar to + Defines realtime (i.e. wallclock) timers with calendar event expressions. See + systemd.time7 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. + Note that timers do not necessarily expire at the precise time configured with this setting, as + it is subject to the AccuracySec= setting below. May be specified more than once, in which case the timer unit will trigger whenever any of the specified expressions elapse. Moreover calendar timers and monotonic timers (see above) may be @@ -205,7 +201,15 @@ If the empty string is assigned to any of these options, the list of timers is reset (both OnCalendar= timers and monotonic timers, see above), and all prior assignments - will have no effect. + will have no effect. + + Note that calendar timers might be triggered at unexpected times if the system's realtime clock + is not set correctly. Specifically, on systems that lack a battery-buffered Realtime Clock (RTC) it + might be wise to enable systemd-time-wait-sync.service to ensure the clock is + adjusted to a network time source before the timer event is set up. Timer units + with at least one OnCalendar= expression are automatically ordered after + time-sync.target, which systemd-time-wait-sync.service is + ordered before.