timers defined in the other directives.</para>
<para>These are monotonic timers, independent of wall-clock time and timezones. If the computer is
- temporarily suspended, the monotonic clock pauses, too.</para>
+ temporarily suspended, the monotonic clock generally pauses, too. Note that if
+ <varname>WakeSystem=</varname> is used, a different monotonic clock is selected that continues to
+ advance while the system is suspended and thus can be used as the trigger to resume the
+ system.</para>
<para>If the empty string is assigned to any of these options, the list of timers is reset (both
monotonic timers and <varname>OnCalendar=</varname> timers, see below), and all prior assignments
<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details. To optimize power consumption, make sure to set
this value as high as possible and as low as
- necessary.</para></listitem>
+ necessary.</para>
+
+ <para>Note that this setting is primarily a power saving option that allows coalescing CPU
+ wake-ups. It should not be confused with <varname>RandomizedDelaySec=</varname> (see below) which
+ adds a random value to the time the timer shall elapse next and whose purpose is the opposite: to
+ stretch elapsing of timer events over a longer period to reduce workload spikes. For further details
+ and explanations and how both settings play together, see below.</para></listitem>
</varlistentry>
<varlistentry>
<varname>AccuracySec=1us</varname>.</para></listitem>
</varlistentry>
+ <varlistentry>
+ <term><varname>OnClockChange=</varname></term>
+ <term><varname>OnTimezoneChange=</varname></term>
+
+ <listitem><para>These options take boolean arguments. When true, the service unit will be triggered
+ when the system clock (<constant>CLOCK_REALTIME</constant>) jumps relative to the monotonic clock
+ (<constant>CLOCK_MONOTONIC</constant>), or when the local system timezone is modified. These options
+ can be used alone or in combination with other timer expressions (see above) within the same timer
+ unit. These options default to false.</para></listitem>
+ </varlistentry>
+
<varlistentry>
<term><varname>Unit=</varname></term>
<varlistentry>
<term><varname>Persistent=</varname></term>
- <listitem><para>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 <varname>OnCalendar=</varname>. Defaults
- to <varname>false</varname>.
- </para></listitem>
+ <listitem><para>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 system was powered down. Note that this setting
+ only has an effect on timers configured with <varname>OnCalendar=</varname>. Defaults to
+ <varname>false</varname>.</para>
+
+ <para>Use <command>systemctl clean --what=state …</command> on the timer unit to remove the timestamp
+ file maintained by this option from disk. In particular, use this command before uninstalling a timer
+ unit. See
+ <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> for
+ details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>WakeSystem=</varname></term>
- <listitem><para>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 <varname>false</varname>.</para></listitem>
+ <listitem><para>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
+ <varname>false</varname>.</para>
+
+ <para>Note that this functionality requires privileges and is thus generally only available in the
+ system service manager.</para>
+
+ <para>Note that behaviour of monotonic clock timers (as configured with
+ <varname>OnActiveSec=</varname>, <varname>OnBootSec=</varname>, <varname>OnStartupSec=</varname>,
+ <varname>OnUnitActiveSec=</varname>, <varname>OnUnitInactiveSec=</varname>, see above) is altered
+ depending on this option. If false, a monotonic clock is used that is paused during system suspend
+ (<constant>CLOCK_MONOTONIC</constant>), if true a different monotonic clock is used that continues
+ advancing during system suspend (<constant>CLOCK_BOOTTIME</constant>), see
+ <citerefentry><refentrytitle>clock_getres</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
+ details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RemainAfterElapse=</varname></term>
<listitem><para>Takes a boolean argument. If true, an elapsed
- timer will stay loaded, and its state remains queriable. If
+ timer will stay loaded, and its state remains queryable. 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
projects / thirdparty / systemd.git / blobdiff