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-rw-r--r--man/systemd.timer.xml43
1 files changed, 37 insertions, 6 deletions
diff --git a/man/systemd.timer.xml b/man/systemd.timer.xml
index 5826773a99..fd03bda9cd 100644
--- a/man/systemd.timer.xml
+++ b/man/systemd.timer.xml
@@ -190,13 +190,12 @@
<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
+ 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
+ order to optimize 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>
@@ -204,6 +203,38 @@
this value as high as possible and as low as
necessary.</para></listitem>
</varlistentry>
+
+ <varlistentry>
+ <term><varname>RandomSec=</varname></term>
+
+ <listitem><para>Delay the timer by a randomly selected, evenly
+ distributed amount of time between 0 and the specified time
+ value. Defaults to 0, indicating that no randomized delay
+ shall be applied. Each timer unit will determine this delay
+ randomly each time it is started, and the delay will simply be
+ added on top of the next determined elapsing time. This is
+ useful to stretch dispatching of similarly configured timer
+ events over a certain amount time, to avoid that they all fire
+ at the same time, possibly resulting in resource
+ congestion. Note the relation to
+ <varname>AccuracySec=</varname> above: the latter allows the
+ service manager to coalesce timer events within a specified
+ time range in order to minimize wakeups, the former does the
+ opposite: it stretches timer events over a time range, to make
+ it unlikely that they fire simultaneously. If
+ <varname>RandomSec=</varname> and
+ <varname>AccuracySec=</varname> are used in conjunction, first
+ the a randomized time is added, and the result is then
+ possibly shifted further to coalesce it with other timer
+ events possibly happening on the system. As mentioned above
+ <varname>AccuracySec=</varname> defaults to 1min and
+ <varname>RandomSec=</varname> to 0, thus encouraging
+ coalescing of timer events. In order to optimally stretch
+ timer events over a certain range of time, make sure to set
+ <varname>RandomSec=</varname> to a higher value, and
+ <varname>AccuracySec=1us</varname>.</para></listitem>
+ </varlistentry>
+
<varlistentry>
<term><varname>Unit=</varname></term>