man/sd_event_set_watchdog.xml

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   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   This file is part of systemd.
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  10   Copyright 2015 Lennart Poettering
  11 -->
  12
  13 <refentry id="sd_event_set_watchdog" xmlns:xi="http://www.w3.org/2001/XInclude">
  14
  15   <refentryinfo>
  16     <title>sd_event_set_watchdog</title>
  17     <productname>systemd</productname>
  18
  19     <authorgroup>
  20       <author>
  21         <contrib>Developer</contrib>
  22         <firstname>Lennart</firstname>
  23         <surname>Poettering</surname>
  24         <email>lennart@poettering.net</email>
  25       </author>
  26     </authorgroup>
  27   </refentryinfo>
  28
  29   <refmeta>
  30     <refentrytitle>sd_event_set_watchdog</refentrytitle>
  31     <manvolnum>3</manvolnum>
  32   </refmeta>
  33
  34   <refnamediv>
  35     <refname>sd_event_set_watchdog</refname>
  36     <refname>sd_event_get_watchdog</refname>
  37
  38     <refpurpose>Enable event loop watchdog support</refpurpose>
  39   </refnamediv>
  40
  41   <refsynopsisdiv>
  42     <funcsynopsis>
  43       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  44
  45       <funcprototype>
  46         <funcdef>int <function>sd_event_set_watchdog</function></funcdef>
  47         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  48         <paramdef>int b</paramdef>
  49       </funcprototype>
  50
  51       <funcprototype>
  52         <funcdef>int <function>sd_event_get_watchdog</function></funcdef>
  53         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  54       </funcprototype>
  55
  56     </funcsynopsis>
  57   </refsynopsisdiv>
  58
  59   <refsect1>
  60     <title>Description</title>
  61
  62     <para><function>sd_event_set_watchdog()</function> may be used to
  63     enable or disable automatic watchdog notification support in the
  64     event loop object specified in the <parameter>event</parameter>
  65     parameter. Specifically, depending on the <parameter>b</parameter>
  66     boolean argument this will make sure the event loop wakes up in
  67     regular intervals and sends watchdog notification messages to the
  68     service manager, if this was requested by the service
  69     manager. Watchdog support is determined with
  70     <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  71     and watchdog messages are sent with
  72     <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>. See
  73     the <varname>WatchdogSec=</varname> setting in
  74     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  75     for details on how to enable watchdog support for a service and
  76     the protocol used. The wake-up interval is chosen as half the
  77     watchdog timeout declared by the service manager via the
  78     <varname>$WATCHDOG_USEC</varname> environment variable. If the
  79     service manager did not request watchdog notifications, or if the
  80     process was not invoked by the service manager this call with a
  81     true <parameter>b</parameter> parameter executes no
  82     operation. Passing a false <parameter>b</parameter> parameter will
  83     disable the automatic sending of watchdog notification messages if
  84     it was enabled before. Newly allocated event loop objects have
  85     this feature disabled.</para>
  86
  87     <para>The first watchdog notification message is sent immediately
  88     when <function>set_event_set_watchdog()</function> is invoked with
  89     a true <parameter>b</parameter> parameter.</para>
  90
  91     <para>The watchdog logic is designed to allow the service manager
  92     to automatically detect services that ceased processing of
  93     incoming events, and thus appear "hung". Watchdog notifications
  94     are sent out only at the beginning of each event loop
  95     iteration. If an event source dispatch function blocks for an
  96     excessively long time and does not return execution to the event
  97     loop quickly, this might hence cause the notification message to
  98     be delayed, and possibly result in abnormal program termination,
  99     as configured in the service unit file.</para>
 100
 101     <para><function>sd_event_get_watchdog()</function> may be used to
 102     determine whether watchdog support was previously requested by a
 103     call to <function>sd_event_set_watchdog()</function> with a true
 104     <parameter>b</parameter> parameter and successfully
 105     enabled.</para>
 106   </refsect1>
 107
 108   <refsect1>
 109     <title>Return Value</title>
 110
 111     <para>On success, <function>sd_event_set_watchdog()</function> and
 112     <function>sd_event_get_watchdog()</function> return a non-zero
 113     positive integer if the service manager requested watchdog support
 114     and watchdog support was successfully enabled. They return zero if
 115     the service manager did not request watchdog support, or if
 116     watchdog support was explicitly disabled with a false
 117     <parameter>b</parameter> parameter. On failure, they return a
 118     negative errno-style error
 119     code.</para>
 120   </refsect1>
 121
 122   <refsect1>
 123     <title>Errors</title>
 124
 125     <para>Returned errors may indicate the following problems:</para>
 126
 127     <variablelist>
 128
 129       <varlistentry>
 130         <term><constant>-ECHILD</constant></term>
 131
 132         <listitem><para>The event loop has been created in a different process.</para></listitem>
 133       </varlistentry>
 134
 135       <varlistentry>
 136         <term><constant>-EINVAL</constant></term>
 137
 138         <listitem><para>The passed event loop object was invalid.</para></listitem>
 139       </varlistentry>
 140
 141     </variablelist>
 142   </refsect1>
 143
 144   <xi:include href="libsystemd-pkgconfig.xml" />
 145
 146   <refsect1>
 147     <title>See Also</title>
 148
 149     <para>
 150       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 151       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 152       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 153       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 154       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 155       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 156       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 157       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 158       <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 159       <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 160       <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 161       <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 162       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 163     </para>
 164   </refsect1>
 165
 166 </refentry>