systemd/man/sd_watchdog_enabled.xml

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

  <refentryinfo>
    <title>sd_watchdog_enabled</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_watchdog_enabled</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_watchdog_enabled</refname>
    <refpurpose>Check whether the service manager expects watchdog keep-alive notifications from a service</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int <function>sd_watchdog_enabled</function></funcdef>
        <paramdef>int <parameter>unset_environment</parameter></paramdef>
        <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>
    <para><function>sd_watchdog_enabled()</function> may be called by
    a service to detect whether the service manager expects regular
    keep-alive watchdog notification events from it, and the timeout
    after which the manager will act on the service if it did not get
    such a notification.</para>

    <para>If the <varname>$WATCHDOG_USEC</varname> environment
    variable is set, and the <varname>$WATCHDOG_PID</varname> variable
    is unset or set to the PID of the current process, the service
    manager expects notifications from this process. The manager will
    usually terminate a service when it does not get a notification
    message within the specified time after startup and after each
    previous message. It is recommended that a daemon sends a
    keep-alive notification message to the service manager every half
    of the time returned here. Notification messages may be sent with
    <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    with a message string of <literal>WATCHDOG=1</literal>.</para>

    <para>If the <parameter>unset_environment</parameter> parameter is
    non-zero, <function>sd_watchdog_enabled()</function> will unset
    the <varname>$WATCHDOG_USEC</varname> and
    <varname>$WATCHDOG_PID</varname> environment variables before
    returning (regardless of whether the function call itself
    succeeded or not). Those variables are no longer inherited by
    child processes. Further calls to
    <function>sd_watchdog_enabled()</function> will also return with
    zero.</para>

    <para>If the <parameter>usec</parameter> parameter is non-NULL,
    <function>sd_watchdog_enabled()</function> will write the timeout
    in µs for the watchdog logic to it.</para>

    <para>To enable service supervision with the watchdog logic, use
    <varname>WatchdogSec=</varname> in service files. See
    <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for details.</para>

    <para>Use
    <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    to enable automatic watchdog support in
    <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>-based event loops.</para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>On failure, this call returns a negative errno-style error
    code. If the service manager expects watchdog keep-alive
    notification messages to be sent, &gt; 0 is returned, otherwise 0
    is returned. Only if the return value is &gt; 0, the
    <parameter>usec</parameter> parameter is valid after the
    call.</para>
  </refsect1>

  <refsect1>
    <title>Notes</title>

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

    <para>Internally, this functions parses the
    <varname>$WATCHDOG_PID</varname> and
    <varname>$WATCHDOG_USEC</varname> environment variable. The call
    will ignore these variables if <varname>$WATCHDOG_PID</varname>
    does not contain the PID of the current process, under the
    assumption that in that case, the variables were set for a
    different process further up the process tree.</para>
  </refsect1>

  <refsect1>
    <title>Environment</title>

    <variablelist class='environment-variables'>
      <varlistentry>
        <term><varname>$WATCHDOG_PID</varname></term>

        <listitem><para>Set by the system manager for supervised
        process for which watchdog support is enabled, and contains
        the PID of that process. See above for
        details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$WATCHDOG_USEC</varname></term>

        <listitem><para>Set by the system manager for supervised
        process for which watchdog support is enabled, and contains
        the watchdog timeout in µs See above for
        details.</para></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>History</title>

    <para>The watchdog functionality and the
    <varname>$WATCHDOG_USEC</varname> variable were added in
    systemd-41.</para>

    <para><function>sd_watchdog_enabled()</function> function was
    added in systemd-209. Since that version, the
    <varname>$WATCHDOG_PID</varname> variable is also set.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>