</refnamediv>
<refsynopsisdiv>
- <para><filename>systemd.timer</filename></para>
+ <para><filename><replaceable>timer</replaceable>.timer</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>A unit configuration file whose name ends in
- <filename>.timer</filename> encodes information about
+ <literal>.timer</literal> encodes information about
a timer controlled and supervised by systemd, for
timer-based activation.</para>
defines. The options specific to the [Timer] section
of timer units are the following:</para>
- <variablelist>
+ <variablelist class='unit-directives'>
<varlistentry>
<term><varname>OnActiveSec=</varname></term>
<term><varname>OnBootSec=</varname></term>
machine was booted
up. <varname>OnStartupSec=</varname>
defines a timer relative to when
- systemd was
+ systemd was first
started. <varname>OnUnitActiveSec=</varname>
defines a timer relative to when the
unit the timer is activating was last
combined of the same and of different
types. For example, by combining
<varname>OnBootSec=</varname> and
- <varname>OnUnitActiveSec=</varname> it is
+ <varname>OnUnitActiveSec=</varname>, it is
possible to define a timer that
elapses in regular intervals and
activates a specific service each
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
+ about the syntax of time spans, see
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
<para>If a timer configured with
<para>These are monotonic timers,
independent of wall-clock time and timezones. If the
computer is temporarily suspended, the
- monotonic clock stops too.</para></listitem>
+ monotonic clock stops too.</para>
+
+ <para>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.</para>
+
+ <para>Note that timers do not
+ necessarily expire at the precise
+ time configured with these settings,
+ as they are subject to the
+ <varname>AccuracySec=</varname>
+ setting below.</para></listitem>
</varlistentry>
<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.</para></listitem>
+ calendar event expressions. Otherwise,
+ the semantics are similar to
+ <varname>OnActiveSec=</varname> and
+ related settings.</para>
+
+ <para>Note that timers do not
+ necessarily expire 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
+ elapse 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
when this timer elapses. The argument is a
unit name, whose suffix is not
- <filename>.timer</filename>. If not
+ <literal>.timer</literal>. If not
specified, this value defaults to a
service that has the same name as the
timer unit, except for the
<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>
~ianmdlvl / elogind.git / blobdiff