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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"

"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<refentry id="sd_event_set_watchdog" xmlns:xi="http://www.w3.org/2001/XInclude">

<refentryinfo>

<title>sd_event_set_watchdog</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>Developer</contrib>

<firstname>Lennart</firstname>

<surname>Poettering</surname>

<email>lennart@poettering.net</email>

</author>

</authorgroup>

</refentryinfo>

<refmeta>

<refentrytitle>sd_event_set_watchdog</refentrytitle>

<manvolnum>3</manvolnum>

</refmeta>

<refnamediv>

<refname>sd_event_set_watchdog</refname>

<refname>sd_event_get_watchdog</refname>

<refpurpose>Enable event loop watchdog support</refpurpose>

</refnamediv>

<refsynopsisdiv>

<funcsynopsis>

<funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>

<funcprototype>

<funcdef>int <function>sd_event_set_watchdog</function></funcdef>

<paramdef>sd_event *<parameter>event</parameter></paramdef>

<paramdef>int b</paramdef>

</funcprototype>

<funcprototype>

<funcdef>int <function>sd_event_get_watchdog</function></funcdef>

<paramdef>sd_event *<parameter>event</parameter></paramdef>

</funcprototype>

</funcsynopsis>

</refsynopsisdiv>

<refsect1>

<title>Description</title>

<para><function>sd_event_set_watchdog()</function> may be used to

enable or disable automatic watchdog notification support in the

event loop object specified in the <parameter>event</parameter>

parameter. Specifically, depending on the <parameter>b</parameter>

boolean argument this will make sure the event loop wakes up in

regular intervals and sends watchdog notification messages to the

service manager, if this was requested by the service

manager. Watchdog support is determined with

<citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

and watchdog messages are sent with

<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>. See

the <varname>WatchdogSec=</varname> setting in

<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>

for details on how to enable watchdog support for a service and

the protocol used. The wake-up interval is chosen as half the

watchdog timeout declared by the service manager via the

<varname>$WATCHDOG_USEC</varname> environment variable. If the

service manager did not request watchdog notifications, or if the

process was not invoked by the service manager this call with a

true <parameter>b</parameter> parameter executes no

operation. Passing a false <parameter>b</parameter> parameter will

disable the automatic sending of watchdog notification messages if

it was enabled before. Newly allocated event loop objects have

this feature disabled.</para>

<para>The first watchdog notification message is sent immediately

when <function>set_event_set_watchdog()</function> is invoked with

a true <parameter>b</parameter> parameter.</para>

<para>The watchdog logic is designed to allow the service manager

to automatically detect services that ceased processing of

incoming events, and thus appear "hung". Watchdog notifications

are sent out only at the beginning of each event loop

iteration. If an event source dispatch function blocks for an

excessively long time and does not return execution to the event

loop quickly, this might hence cause the notification message to

be delayed, and possibly result in abnormal program termination,

as configured in the service unit file.</para>

<para><function>sd_event_get_watchdog()</function> may be used to

determine whether watchdog support was previously requested by a

call to <function>sd_event_set_watchdog()</function> with a true

<parameter>b</parameter> parameter and successfully

enabled.</para>

</refsect1>

<refsect1>

<title>Return Value</title>

<para>On success, <function>sd_event_set_watchdog()</function> and

<function>sd_event_get_watchdog()</function> return a non-zero

positive integer if the service manager requested watchdog support

and watchdog support was successfully enabled. They return zero if

the service manager did not request watchdog support, or if

watchdog support was explicitly disabled with a false

<parameter>b</parameter> parameter. On failure, they return a

negative errno-style error

code.</para>

</refsect1>

<refsect1>

<title>Errors</title>

<para>Returned errors may indicate the following problems:</para>

<variablelist>

<varlistentry>

<term><constant>-ECHILD</constant></term>

<listitem><para>The event loop has been created in a different process.</para></listitem>

</varlistentry>

<varlistentry>

<term><constant>-EINVAL</constant></term>

<listitem><para>The passed event loop object was invalid.</para></listitem>

</varlistentry>

</variablelist>

</refsect1>

<xi:include href="libsystemd-pkgconfig.xml" />

<refsect1>

<title>See Also</title>

<para>

<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>