systemd/man/sd_notify.xml

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

        <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 service 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> may be called
                by a service to notify the service manager about
                state 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 of
                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 service
                                manager that service startup is
                                finished. This is only used by systemd
                                if the service definition file has
                                Type=notify set. Since there is little
                                value in signaling non-readiness, the
                                only value services should send is
                                <literal>READY=1</literal>
                                (i.e. <literal>READY=0</literal> is
                                not defined).</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>RELOADING=1</term>

                                <listitem><para>Tells the service manager
                                that the service is reloading its
                                configuration. This is useful to allow
                                the service manager to track the service's
                                internal state, and present it to the
                                user. Note that a service that sends
                                this notification must also send a
                                <literal>READY=1</literal>
                                notification when it completed
                                reloading its
                                configuration.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>STOPPING=1</term>

                                <listitem><para>Tells the service manager
                                that the service is beginning its
                                shutdown. This is useful to allow the
                                service manager to track the service's
                                internal state, and present it to the
                                user.</para></listitem>
                        </varlistentry>

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

                                <listitem><para>Passes a single-line
                                UTF-8 status string back to the service manager
                                that describes the service 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:
                                <literal>STATUS=Completed 66% of file
                                system
                                check...</literal></para></listitem>
                        </varlistentry>

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

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

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

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

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

                                <listitem><para>The main pid of the
                                service, in case the service manager did
                                not fork off the process
                                itself. Example:
                                <literal>MAINPID=4711</literal></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 information how to enable this
                                functionality and
                                <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                for the details of how the service can
                                check if the the watchdog is enabled.
                                </para></listitem>
                        </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 service 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
                the status was sent, these functions return with a
                positive return value. In order to support both, init
                systems that implement this scheme and those which
                do not, it is generally recommended to ignore the return
                value of this call.</para>
        </refsect1>

        <refsect1>
                <title>Notes</title>

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

                <para>Internally, these functions send a single
                datagram with the state string as payload to the
                <constant>AF_UNIX</constant> socket referenced in the
                <varname>$NOTIFY_SOCKET</varname> environment
                variable. If the first character of
                <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the string is
                understood as Linux abstract namespace socket. The
                datagram is accompanied by the process credentials of
                the sending service, 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 service manager
                                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 service finished starting up, it
                        might issue the following call to notify
                        the service manager:</para>

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

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

                        <para>A service 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 service 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>,
                        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>