diff options
Diffstat (limited to 'man/systemd.timer.xml')
| -rw-r--r-- | man/systemd.timer.xml | 58 |
1 files changed, 49 insertions, 9 deletions
diff --git a/man/systemd.timer.xml b/man/systemd.timer.xml index 3841588820..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> @@ -245,11 +276,20 @@ </varlistentry> <varlistentry> - <term><varname>RemainAfterExit=</varname></term> + <term><varname>RemainAfterElapse=</varname></term> <listitem><para>Takes a boolean argument. If true, an elapsed - timer will stay loaded, and its state remains - queriable. Defaults to + timer will stay loaded, and its state remains queriable. 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 + elapse. Note that this setting has an effect on repeatedly + starting the a timer unit that only elapses once: if + <varname>RemainAfterElapse=</varname> is on, it will not be + started again, and is guaranteed to elapse only once. However, + if <varname>RemainAfterLeapse=</varname> is off, it might be + started again if it is already elapsed, and thus be triggered + multiple times. Defaults to <varname>yes</varname>.</para></listitem> </varlistentry> </variablelist> |