man/sd_event_set_watchdog.xml

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  23
  24 <refentry id="sd_event_set_watchdog" xmlns:xi="http://www.w3.org/2001/XInclude">
  25
  26   <refentryinfo>
  27     <title>sd_event_set_watchdog</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>Developer</contrib>
  33         <firstname>Lennart</firstname>
  34         <surname>Poettering</surname>
  35         <email>lennart@poettering.net</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>sd_event_set_watchdog</refentrytitle>
  42     <manvolnum>3</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sd_event_set_watchdog</refname>
  47     <refname>sd_event_get_watchdog</refname>
  48
  49     <refpurpose>Enable event loop watchdog support</refpurpose>
  50   </refnamediv>
  51
  52   <refsynopsisdiv>
  53     <funcsynopsis>
  54       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  55
  56       <funcprototype>
  57         <funcdef>int <function>sd_event_set_watchdog</function></funcdef>
  58         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  59         <paramdef>int b</paramdef>
  60       </funcprototype>
  61
  62       <funcprototype>
  63         <funcdef>int <function>sd_event_get_watchdog</function></funcdef>
  64         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  65       </funcprototype>
  66
  67     </funcsynopsis>
  68   </refsynopsisdiv>
  69
  70   <refsect1>
  71     <title>Description</title>
  72
  73     <para><function>sd_event_set_watchdog()</function> may be used to
  74     enable or disable automatic watchdog notification support in the
  75     event loop object specified in the <parameter>event</parameter>
  76     parameter. Specifically, depending on the <parameter>b</parameter>
  77     boolean argument this will make sure the event loop wakes up in
  78     regular intervals and sends watchdog notification messages to the
  79     service manager, if this was requested by the service
  80     manager. Watchdog support is determined with
  81     <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  82     and watchdog messages are sent with
  83     <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>. See
  84     the <varname>WatchdogSec=</varname> setting in
  85     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  86     for details on how to enable watchdog support for a service and
  87     the protocol used. The wake-up interval is chosen as half the
  88     watchdog timeout declared by the service manager via the
  89     <varname>$WATCHDOG_USEC</varname> environment variable. If the
  90     service manager did not request watchdog notifications, or if the
  91     process was not invoked by the service manager this call with a
  92     true <parameter>b</parameter> parameter executes no
  93     operation. Passing a false <parameter>b</parameter> parameter will
  94     disable the automatic sending of watchdog notification messages if
  95     it was enabled before. Newly allocated event loop objects have
  96     this feature disabled.</para>
  97
  98     <para>The first watchdog notification message is sent immediately
  99     when <function>set_event_set_watchdog()</function> is invoked with
 100     a true <parameter>b</parameter> parameter.</para>
 101
 102     <para>The watchdog logic is designed to allow the service manager
 103     to automatically detect services that ceased processing of
 104     incoming events, and thus appear "hung". Watchdog notifications
 105     are sent out only at the beginning of each event loop
 106     iteration. If an event source dispatch function blocks for an
 107     excessively long time and does not return execution to the event
 108     loop quickly, this might hence cause the notification message to
 109     be delayed, and possibly result in abnormal program termination,
 110     as configured in the service unit file.</para>
 111
 112     <para><function>sd_event_get_watchdog()</function> may be used to
 113     determine whether watchdog support was previously requested by a
 114     call to <function>sd_event_set_watchdog()</function> with a true
 115     <parameter>b</parameter> parameter and successfully
 116     enabled.</para>
 117   </refsect1>
 118
 119   <refsect1>
 120     <title>Return Value</title>
 121
 122     <para>On success, <function>sd_event_set_watchdog()</function> and
 123     <function>sd_event_get_watchdog()</function> return a non-zero
 124     positive integer if the service manager requested watchdog support
 125     and watchdog support was successfully enabled. They return zero if
 126     the service manager did not request watchdog support, or if
 127     watchdog support was explicitly disabled with a false
 128     <parameter>b</parameter> parameter. On failure, they return a
 129     negative errno-style error
 130     code.</para>
 131   </refsect1>
 132
 133   <refsect1>
 134     <title>Errors</title>
 135
 136     <para>Returned errors may indicate the following problems:</para>
 137
 138     <variablelist>
 139
 140       <varlistentry>
 141         <term><constant>-ECHILD</constant></term>
 142
 143         <listitem><para>The event loop has been created in a different process.</para></listitem>
 144       </varlistentry>
 145
 146       <varlistentry>
 147         <term><constant>-EINVAL</constant></term>
 148
 149         <listitem><para>The passed event loop object was invalid.</para></listitem>
 150       </varlistentry>
 151
 152     </variablelist>
 153   </refsect1>
 154
 155   <xi:include href="libsystemd-pkgconfig.xml" />
 156
 157   <refsect1>
 158     <title>See Also</title>
 159
 160     <para>
 161       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 162       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 163       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 164       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 165       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 166       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 167       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 168       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 169       <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 170       <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 171       <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 172       <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 173       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 174     </para>
 175   </refsect1>
 176
 177 </refentry>