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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 2010 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
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  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
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  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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  Lesser General Public License for more details.
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  You should have received a copy of the GNU Lesser General Public License
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  along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->

<refentry id="sd_notify">

        <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 init system about start-up completion and other daemon status changes</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <funcsynopsis>
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                        <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
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                        <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>
                parameter is non-zero <function>sd_notify()</function>
                will unset the <varname>$NOTIFY_SOCKET</varname>
                environment variable before returning (regardless
                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
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                should contain an newline-separated list of variable
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                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
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                                value in signalling non-readiness, the
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                                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
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                                is free-form and can be used for
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                                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>
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                        <varlistentry>
                                <term>WATCHDOG=1</term>

                                <listitem><para>Tells systemd to
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                                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
                                <varname>WATCHDOG_USEC=</varname>
                                environment variable has been set for
                                the service process, in every half the
                                time interval that is specified in the
                                variable.</para></listitem>
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                        </varlistentry>
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                </variablelist>

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                <para>It is recommended to prefix variable names that
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                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
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                <function>sd_notify()</function> but takes a
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                <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
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                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
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                systems that implement this scheme and those which
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                don't, it is generally recommended to ignore the return
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                value of this call.</para>
        </refsect1>

        <refsect1>
                <title>Notes</title>

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

                <para>Internally, these functions send a single
                datagram with the state string as payload to the
                AF_UNIX socket referenced in the
                <varname>$NOTIFY_SOCKET</varname> environment
                variable. If the first character of
                <varname>$NOTIFY_SOCKET</varname> is @ the string is
                understood as Linux abstract namespace socket. The
                datagram is accompanied by the process credentials of
                the sending daemon, using SCM_CREDENTIALS.</para>

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                <para>For details about the algorithms check the
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                liberally licensed reference implementation sources:
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                <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/sd-daemon.c"/>
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                resp. <ulink
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                url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
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                <para><function>sd_notify()</function> and
                <function>sd_notifyf()</function> are implemented in
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                the reference implementation's
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                <filename>sd-daemon.c</filename> and
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                <filename>sd-daemon.h</filename> files. These
                interfaces are available as shared library, which can
                be compiled and linked to with the
                <literal>libsystemd-daemon</literal>
                <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                file. Alternatively, applications consuming these APIs
                may copy the implementation into their source tree. For
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                more details about the reference implementation see
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                <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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                <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>
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        </refsect1>

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        <refsect1>
                <title>Environment</title>

                <variablelist>
                        <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>

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        <refsect1>
                <title>Examples</title>

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

                        <para>When a daemon finished starting up, it
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                        might issue the following call to notify
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                        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>
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                        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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                        <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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                        <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>