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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
        "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<!--
  This file is part of systemd.

  Copyright 2013 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
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<refentry id="sd_watchdog_enabled">

        <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>const 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 <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 whether the function call
                itself succeeded or not). Further calls to
                <function>sd_watchdog_enabled()</function> will then
                return with zero, but the variable is no longer
                inherited by child processes.</para>

                <para>If the <parameter>usec</parameter> parameter is
                non-NULL <function>sd_watchdog_enabled()</function>
                will return the timeout in µs for the watchdog
                logic. The service manager will usually terminate a
                service when it did 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>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>
        </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>

                <para>This function is provided by the reference
                implementation of APIs for new-style daemons and
                distributed with the systemd package. The algorithm
                it implements is simple, and can easily be
                reimplemented in daemons if it is important to support
                this interface without using the reference
                implementation.</para>

                <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 containe 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>

                <para>For details about the algorithm check the
                liberally licensed reference implementation sources:
                <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c"/>
                and <ulink
                url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>

                <para><function>sd_watchdog_enabled()</function> is
                implemented in the reference implementation's
                <filename>sd-daemon.c</filename> and
                <filename>sd-daemon.h</filename> files. These
                interfaces are available as shared library, which can
                be compiled and linked to with the
                <constant>libsystemd-daemon</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                file. Alternatively, applications consuming these APIs
                may copy the implementation into their source
                tree. For more details about the reference
                implementation see
                <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

                <para>If the reference implementation is used as
                drop-in files and -DDISABLE_SYSTEMD is set during
                compilation, these functions will always return 0 and
                otherwise become a NOP.</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>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>
                </para>
        </refsect1>

</refentry>