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

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

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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>
        </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>
                </para>
        </refsect1>

</refentry>