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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">

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  Copyright 2010 Lennart Poettering

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<refentry id="sd_notify"
        xmlns:xi="http://www.w3.org/2001/XInclude">
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        <refentryinfo>
                <title>sd_notify</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_notify</refentrytitle>
                <manvolnum>3</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>sd_notify</refname>
                <refname>sd_notifyf</refname>
                <refpurpose>Notify service manager about start-up completion and other daemon status changes</refpurpose>
        </refnamediv>

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

                        <funcprototype>
                                <funcdef>int <function>sd_notify</function></funcdef>
                                <paramdef>int <parameter>unset_environment</parameter></paramdef>
                                <paramdef>const char *<parameter>state</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_notifyf</function></funcdef>
                                <paramdef>int <parameter>unset_environment</parameter></paramdef>
                                <paramdef>const char *<parameter>format</parameter></paramdef>
                                <paramdef>...</paramdef>
                        </funcprototype>
                </funcsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>
                <para><function>sd_notify()</function> shall be called
                by a daemon to notify the init system about status
                changes. It can be used to send arbitrary information,
                encoded in an environment-block-like string. Most
                importantly it can be used for start-up completion
                notification.</para>

                <para>If the <parameter>unset_environment</parameter>
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                parameter is non-zero, <function>sd_notify()</function>
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                will unset the <varname>$NOTIFY_SOCKET</varname>
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                environment variable before returning (regardless of
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                whether the function call itself succeeded or
                not). Further calls to
                <function>sd_notify()</function> will then fail, but
                the variable is no longer inherited by child
                processes.</para>

                <para>The <parameter>state</parameter> parameter
                should contain a newline-separated list of variable
                assignments, similar in style to an environment
                block. A trailing newline is implied if none is
                specified. The string may contain any kind of variable
                assignments, but the following shall be considered
                well-known:</para>

                <variablelist>
                        <varlistentry>
                                <term>READY=1</term>

                                <listitem><para>Tells the init system
                                that daemon startup is finished. This
                                is only used by systemd if the service
                                definition file has Type=notify
                                set. The passed argument is a boolean
                                "1" or "0". Since there is little
                                value in signaling non-readiness, the
                                only value daemons should send is
                                "READY=1".</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>STATUS=...</term>

                                <listitem><para>Passes a single-line
                                status string back to the init system
                                that describes the daemon state. This
                                is free-form and can be used for
                                various purposes: general state
                                feedback, fsck-like programs could
                                pass completion percentages and
                                failing programs could pass a human
                                readable error message. Example:
                                "STATUS=Completed 66% of file system
                                check..."</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>ERRNO=...</term>

                                <listitem><para>If a daemon fails, the
                                errno-style error code, formatted as
                                string. Example: "ERRNO=2" for
                                ENOENT.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>BUSERROR=...</term>

                                <listitem><para>If a daemon fails, the
                                D-Bus error-style error code. Example:
                                "BUSERROR=org.freedesktop.DBus.Error.TimedOut"</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>MAINPID=...</term>

                                <listitem><para>The main pid of the
                                daemon, in case the init system did
                                not fork off the process
                                itself. Example:
                                "MAINPID=4711"</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>WATCHDOG=1</term>

                                <listitem><para>Tells systemd to
                                update the watchdog timestamp. This is
                                the keep-alive ping that services need
                                to issue in regular intervals if
                                <varname>WatchdogSec=</varname> is
                                enabled for it. See
                                <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                                for details. It is recommended to send
                                this message if the
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                                <varname>$WATCHDOG_PID</varname>
                                environment variable has been set to
                                the PID of the service process, in
                                every half the time interval that is
                                specified in the
                                <varname>$WATCHDOG_USEC</varname>
                                environment variable. See
                                <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                for details.</para></listitem>
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                        </varlistentry>
                </variablelist>

                <para>It is recommended to prefix variable names that
                are not shown in the list above with
                <varname>X_</varname> to avoid namespace
                clashes.</para>

                <para>Note that systemd will accept status data sent
                from a daemon only if the
                <varname>NotifyAccess=</varname> option is correctly
                set in the service definition file. See
                <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                for details.</para>

                <para><function>sd_notifyf()</function> is similar to
                <function>sd_notify()</function> but takes a
                <function>printf()</function>-like format string plus
                arguments.</para>
        </refsect1>

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

                <para>On failure, these calls return a negative
                errno-style error code. If
                <varname>$NOTIFY_SOCKET</varname> was not set and
                hence no status data could be sent, 0 is returned. If
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                the status was sent, these functions return with a
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                positive return value. In order to support both, init
                systems that implement this scheme and those which
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                do not, it is generally recommended to ignore the return
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                value of this call.</para>
        </refsect1>

        <refsect1>
                <title>Notes</title>

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                <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
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                <para>Internally, these functions send a single
                datagram with the state string as payload to the
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                <constant>AF_UNIX</constant> socket referenced in the
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                <varname>$NOTIFY_SOCKET</varname> environment
                variable. If the first character of
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                <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the string is
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                understood as Linux abstract namespace socket. The
                datagram is accompanied by the process credentials of
                the sending daemon, using SCM_CREDENTIALS.</para>
        </refsect1>

        <refsect1>
                <title>Environment</title>

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

                                <listitem><para>Set by the init system
                                for supervised processes for status
                                and start-up completion
                                notification. This environment variable
                                specifies the socket
                                <function>sd_notify()</function> talks
                                to. See above for details.</para></listitem>
                        </varlistentry>
                </variablelist>
        </refsect1>

        <refsect1>
                <title>Examples</title>

                <example>
                        <title>Start-up Notification</title>

                        <para>When a daemon finished starting up, it
                        might issue the following call to notify
                        the init system:</para>

                        <programlisting>sd_notify(0, "READY=1");</programlisting>
                </example>

                <example>
                        <title>Extended Start-up Notification</title>

                        <para>A daemon could send the following after
                        completing initialization:</para>

                        <programlisting>sd_notifyf(0, "READY=1\n"
              "STATUS=Processing requests...\n"
              "MAINPID=%lu",
              (unsigned long) getpid());</programlisting>
                </example>

                <example>
                        <title>Error Cause Notification</title>

                        <para>A daemon could send the following shortly before exiting, on failure</para>

                        <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
              "ERRNO=%i",
              strerror(errno),
              errno);</programlisting>
                </example>
        </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>,
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                        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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                </para>
        </refsect1>

</refentry>