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[thirdparty/systemd.git] / man / sd_event_set_watchdog.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1+ -->

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

  <refentryinfo>
    <title>sd_event_set_watchdog</title>
    <productname>systemd</productname>
  </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>

    <refsect2>
      <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>
    </refsect2>
  </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_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_defer</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>