systemd/man/systemd-notify.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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<refentry id="systemd-notify"
    xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>systemd-notify</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd-notify</refentrytitle>
    <manvolnum>1</manvolnum>
  </refmeta>

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

  <refsynopsisdiv>
    <cmdsynopsis>
      <command>systemd-notify</command> <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="opt" rep="repeat">VARIABLE=VALUE</arg>
    </cmdsynopsis>
    <cmdsynopsis>
      <command>systemd-notify</command> <arg>--exec</arg> <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="opt" rep="repeat">VARIABLE=VALUE</arg> <arg>;</arg> <arg rep="repeat">CMDLINE</arg>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><command>systemd-notify</command> may be called by service scripts to notify the invoking service
    manager about status changes. It can be used to send arbitrary information, encoded in an
    environment-block-like list of strings. Most importantly, it can be used for start-up completion
    notification.</para>

    <para>This is mostly just a wrapper around <function>sd_notify()</function> and makes this functionality
    available to shell scripts. For details see
    <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    </para>

    <para>The command line may carry a list of environment variables to send as part of the status
    update.</para>

    <para>Note that systemd will refuse reception of status updates from this command unless
    <varname>NotifyAccess=</varname> is appropriately set for the service unit this command is called
    from. See
    <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
    details.</para>

    <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only
    if either the sending process is still around at the time the service manager processes the message, or
    if the sending process is explicitly runtime-tracked by the service manager. The latter is the case if
    the service manager originally forked off the process, i.e. on all processes that match
    <varname>NotifyAccess=</varname><option>main</option> or
    <varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit
    sends an <function>sd_notify()</function> message and immediately exits, the service manager might not be
    able to properly attribute the message to the unit, and thus will ignore it, even if
    <varname>NotifyAccess=</varname><option>all</option> is set for it. To address this
    <command>systemd-notify</command> will wait until the notification message has been processed by the
    service manager. When <option>--no-block</option> is used, this synchronization for reception of
    notifications is disabled, and hence the aforementioned race may occur if the invoking process is not the
    service manager or spawned by the service manager.</para>

    <para><command>systemd-notify</command> will first attempt to invoke <function>sd_notify()</function>
    pretending to have the PID of the parent process of <command>systemd-notify</command> (i.e. the invoking
    process). This will only succeed when invoked with sufficient privileges.  On failure, it will then fall
    back to invoking it under its own PID. This behaviour is useful in order that when the tool is invoked
    from a shell script the shell process — and not the <command>systemd-notify</command> process — appears
    as sender of the message, which in turn is helpful if the shell process is the main process of a service,
    due to the limitations of <varname>NotifyAccess=</varname><option>all</option>. Use the
    <option>--pid=</option> switch to tweak this behaviour.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>The following options are understood:</para>

    <variablelist>
      <varlistentry>
        <term><option>--ready</option></term>

        <listitem><para>Inform the invoking service manager about service start-up or configuration reload
        completion. This is equivalent to <command>systemd-notify READY=1</command>. For details about the
        semantics of this option see
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--reloading</option></term>

        <listitem><para>Inform the invoking service manager about the beginning of a configuration reload
        cycle. This is equivalent to <command>systemd-notify RELOADING=1</command> (but implicitly also sets
        a <varname>MONOTONIC_USEC=</varname> field as required for <varname>Type=notify-reload</varname>
        services, see
        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        for details). For details about the semantics of this option see
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

        <xi:include href="version-info.xml" xpointer="v253"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--stopping</option></term>

        <listitem><para>Inform the invoking service manager about the beginning of the shutdown phase of the
        service. This is equivalent to <command>systemd-notify STOPPING=1</command>. For details about the
        semantics of this option see
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

        <xi:include href="version-info.xml" xpointer="v253"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--pid=</option></term>

        <listitem><para>Inform the service manager about the main PID of the service. Takes a PID as argument.
        If the argument is specified as <literal>auto</literal> or omitted, the PID of the process that
        invoked <command>systemd-notify</command> is used, except if that's the service manager. If the
        argument is specified as <literal>self</literal>, the PID of the <command>systemd-notify</command>
        command itself is used, and if <literal>parent</literal> is specified the calling process' PID is
        used — even if it is the service manager. <option>--pid=auto</option> is equivalent to <command>systemd-notify
        MAINPID=$PID</command>. For details about the semantics of this option see
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

        <para>If this switch is used in an <command>systemd-notify</command> invocation from a process that
        shall become the new main process of a service — and which is not the process forked off by the
        service manager (or the current main process) —, then it is essential to set
        <varname>NotifyAccess=all</varname> in the service unit file, or otherwise the notification will be
        ignored for security reasons. See
        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        for details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--uid=<replaceable>USER</replaceable></option></term>

        <listitem><para>Set the user ID to send the notification from. Takes a UNIX user name or numeric UID. When
        specified the notification message will be sent with the specified UID as sender, in place of the user the
        command was invoked as. This option requires sufficient privileges in order to be able manipulate the user
        identity of the process.</para>

        <xi:include href="version-info.xml" xpointer="v237"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--status=</option></term>

        <listitem><para>Send a free-form human readable status string for the daemon to the service
        manager. This option takes the status string as argument. This is equivalent to
        <command>systemd-notify STATUS=…</command>. For details about the semantics of this option see
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This
        information is shown in
        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
        <command>status</command> output, among other places.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--booted</option></term>

        <listitem><para>Returns 0 if the system was booted up with systemd, non-zero otherwise. If this
        option is passed, no message is sent. This option is hence unrelated to the other options. For
        details about the semantics of this option, see
        <citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>. An
        alternate way to check for this state is to call
        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> with
        the <command>is-system-running</command> command. It will return <literal>offline</literal> if the
        system was not booted with systemd.  </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--no-block</option></term>

        <listitem><para>Do not synchronously wait for the requested operation to finish.  Use of this option
        is only recommended when <command>systemd-notify</command> is spawned by the service manager, or when
        the invoking process is directly spawned by the service manager and has enough privileges to allow
        <command>systemd-notify</command> to send the notification on its behalf. Sending notifications with
        this option set is prone to race conditions in all other cases.</para>

        <xi:include href="version-info.xml" xpointer="v246"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--exec</option></term>

        <listitem><para>If specified <command>systemd-notify</command> will execute another command line
        after it completed its operation, replacing its own process. If used, the list of assignments to
        include in the message sent must be followed by a <literal>;</literal> character (as separate
        argument), followed by the command line to execute. This permits "chaining" of commands, i.e. issuing
        one operation, followed immediately by another, without changing PIDs.</para>

        <para>Note that many shells interpret <literal>;</literal> as their own separator for command lines,
        hence when <command>systemd-notify</command> is invoked from a shell the semicolon must usually be
        escaped as <literal>\;</literal>.</para>

        <xi:include href="version-info.xml" xpointer="v254"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--fd=</option></term>

        <listitem><para>Send a file descriptor along with the notification message. This is useful when
        invoked in services that have the <varname>FileDescriptorStoreMax=</varname> setting enabled, see
        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        for details. The specified file descriptor must be passed to <command>systemd-notify</command> when
        invoked. This option may be used multiple times to pass multiple file descriptors in a single
        notification message.</para>

        <para>To use this functionality from a
        <citerefentry project='man-pages'><refentrytitle>bash</refentrytitle><manvolnum>1</manvolnum></citerefentry>
        shell, use an expression like the following:</para>
        <programlisting>systemd-notify --fd=4 --fd=5 4&lt;/some/file 5&lt;/some/other/file</programlisting>

        <xi:include href="version-info.xml" xpointer="v254"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--fdname=</option></term>

        <listitem><para>Set a name to assign to the file descriptors passed via <option>--fd=</option> (see
        above). This controls the <literal>FDNAME=</literal> field. This setting may only be specified once,
        and applies to all file descriptors passed. Invoke this tool multiple times in case multiple file
        descriptors with different file descriptor names shall be submitted.</para>

        <xi:include href="version-info.xml" xpointer="v254"/></listitem>
      </varlistentry>

      <xi:include href="standard-options.xml" xpointer="help" />
      <xi:include href="standard-options.xml" xpointer="version" />
    </variablelist>

  </refsect1>

  <refsect1>
    <title>Exit status</title>

    <para>On success, 0 is returned, a non-zero failure code
    otherwise.</para>
  </refsect1>

  <refsect1>
    <title>Example</title>

    <example>
      <title>Start-up Notification and Status Updates</title>

      <para>A simple shell daemon that sends start-up notifications after having set up its communication
      channel. During runtime it sends further status updates to the init system:</para>

      <programlisting>#!/bin/sh

mkfifo /tmp/waldo
systemd-notify --ready --status="Waiting for data…"

while : ; do
        read -r a &lt; /tmp/waldo
        systemd-notify --status="Processing $a"

        # Do something with $a …

        systemd-notify --status="Waiting for data…"
done</programlisting>
    </example>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>
</refentry>