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-rw-r--r--man/systemd.timer.xml62
1 files changed, 58 insertions, 4 deletions
diff --git a/man/systemd.timer.xml b/man/systemd.timer.xml
index 659bc81ccd..484287ccf6 100644
--- a/man/systemd.timer.xml
+++ b/man/systemd.timer.xml
@@ -163,7 +163,14 @@
to any of these options, the list of
timers is reset, and all prior
assignments will have no
- effect.</para></listitem>
+ effect.</para>
+
+ <para>Note that timers are not
+ necessarily expired at the precise
+ time configured with these settings,
+ as they are subject to the
+ <varname>AccuracySec=</varname>
+ setting below.</para></listitem>
</varlistentry>
@@ -171,17 +178,62 @@
<term><varname>OnCalendar=</varname></term>
<listitem><para>Defines realtime
- (i.e. wallclock) timers via calendar
+ (i.e. wallclock) timers with calendar
event expressions. See
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for more information on the syntax of
calendar event expressions. Otherwise
the semantics are similar to
<varname>OnActiveSec=</varname> and
- related settings.</para></listitem>
+ related settings.</para>
+
+ <para>Note that timers are not
+ necessarily expired at the precise
+ time configured with this setting,
+ as it is subject to the
+ <varname>AccuracySec=</varname>
+ setting below.</para></listitem>
</varlistentry>
<varlistentry>
+ <term><varname>AccuracySec=</varname></term>
+
+ <listitem><para>Specify the accuracy
+ the timer shall elapse with. Defaults
+ to 1min. The timer is scheduled to
+ expire within a time window starting
+ with the time specified in
+ <varname>OnCalendar=</varname>,
+ <varname>OnActiveSec=</varname>,
+ <varname>OnBootSec=</varname>,
+ <varname>OnStartupSec=</varname>,
+ <varname>OnUnitActiveSec=</varname> or
+ <varname>OnUnitInactiveSec=</varname>
+ and ending the time configured with
+ <varname>AccuracySec=</varname>
+ 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
+ <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
+ <varname>TimerSlackNSec=</varname>
+ setting. See
+ <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>
+ </varlistentry>
+ <varlistentry>
<term><varname>Unit=</varname></term>
<listitem><para>The unit to activate
@@ -208,7 +260,9 @@
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
</para>
</refsect1>