man/sd_event_set_watchdog.xml

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  10   Copyright 2015 Lennart Poettering
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  25
  26 <refentry id="sd_event_set_watchdog" xmlns:xi="http://www.w3.org/2001/XInclude">
  27
  28   <refentryinfo>
  29     <title>sd_event_set_watchdog</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>Developer</contrib>
  35         <firstname>Lennart</firstname>
  36         <surname>Poettering</surname>
  37         <email>lennart@poettering.net</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>sd_event_set_watchdog</refentrytitle>
  44     <manvolnum>3</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>sd_event_set_watchdog</refname>
  49     <refname>sd_event_get_watchdog</refname>
  50
  51     <refpurpose>Enable event loop watchdog support</refpurpose>
  52   </refnamediv>
  53
  54   <refsynopsisdiv>
  55     <funcsynopsis>
  56       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  57
  58       <funcprototype>
  59         <funcdef>int <function>sd_event_set_watchdog</function></funcdef>
  60         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  61         <paramdef>int b</paramdef>
  62       </funcprototype>
  63
  64       <funcprototype>
  65         <funcdef>int <function>sd_event_get_watchdog</function></funcdef>
  66         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  67       </funcprototype>
  68
  69     </funcsynopsis>
  70   </refsynopsisdiv>
  71
  72   <refsect1>
  73     <title>Description</title>
  74
  75     <para><function>sd_event_set_watchdog()</function> may be used to
  76     enable or disable automatic watchdog notification support in the
  77     event loop object specified in the <parameter>event</parameter>
  78     parameter. Specifically, depending on the <parameter>b</parameter>
  79     boolean argument this will make sure the event loop wakes up in
  80     regular intervals and sends watchdog notification messages to the
  81     service manager, if this was requested by the service
  82     manager. Watchdog support is determined with
  83     <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  84     and watchdog messages are sent with
  85     <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>. See
  86     the <varname>WatchdogSec=</varname> setting in
  87     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  88     for details on how to enable watchdog support for a service and
  89     the protocol used. The wake-up interval is chosen as half the
  90     watchdog timeout declared by the service manager via the
  91     <varname>$WATCHDOG_USEC</varname> environment variable. If the
  92     service manager did not request watchdog notifications, or if the
  93     process was not invoked by the service manager this call with a
  94     true <parameter>b</parameter> parameter executes no
  95     operation. Passing a false <parameter>b</parameter> parameter will
  96     disable the automatic sending of watchdog notification messages if
  97     it was enabled before. Newly allocated event loop objects have
  98     this feature disabled.</para>
  99
 100     <para>The first watchdog notification message is sent immediately
 101     when <function>set_event_set_watchdog()</function> is invoked with
 102     a true <parameter>b</parameter> parameter.</para>
 103
 104     <para>The watchdog logic is designed to allow the service manager
 105     to automatically detect services that ceased processing of
 106     incoming events, and thus appear "hung". Watchdog notifications
 107     are sent out only at the beginning of each event loop
 108     iteration. If an event source dispatch function blocks for an
 109     excessively long time and does not return execution to the event
 110     loop quickly, this might hence cause the notification message to
 111     be delayed, and possibly result in abnormal program termination,
 112     as configured in the service unit file.</para>
 113
 114     <para><function>sd_event_get_watchdog()</function> may be used to
 115     determine whether watchdog support was previously requested by a
 116     call to <function>sd_event_set_watchdog()</function> with a true
 117     <parameter>b</parameter> parameter and successfully
 118     enabled.</para>
 119   </refsect1>
 120
 121   <refsect1>
 122     <title>Return Value</title>
 123
 124     <para>On success, <function>sd_event_set_watchdog()</function> and
 125     <function>sd_event_get_watchdog()</function> return a non-zero
 126     positive integer if the service manager requested watchdog support
 127     and watchdog support was successfully enabled. They return zero if
 128     the service manager did not request watchdog support, or if
 129     watchdog support was explicitly disabled with a false
 130     <parameter>b</parameter> parameter. On failure, they return a
 131     negative errno-style error
 132     code.</para>
 133   </refsect1>
 134
 135   <refsect1>
 136     <title>Errors</title>
 137
 138     <para>Returned errors may indicate the following problems:</para>
 139
 140     <variablelist>
 141
 142       <varlistentry>
 143         <term><constant>-ECHILD</constant></term>
 144
 145         <listitem><para>The event loop has been created in a different process.</para></listitem>
 146       </varlistentry>
 147
 148       <varlistentry>
 149         <term><constant>-EINVAL</constant></term>
 150
 151         <listitem><para>The passed event loop object was invalid.</para></listitem>
 152       </varlistentry>
 153
 154     </variablelist>
 155   </refsect1>
 156
 157   <xi:include href="libsystemd-pkgconfig.xml" />
 158
 159   <refsect1>
 160     <title>See Also</title>
 161
 162     <para>
 163       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 164       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 165       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 166       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 167       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 168       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 169       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 170       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 171       <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 172       <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 173       <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 174       <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 175       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 176     </para>
 177   </refsect1>
 178
 179 </refentry>