man: document that start limiting of GC'ed units doesn't work (#7337)

[thirdparty/systemd.git] / man / systemd-notify.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="systemd-notify"
    xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>systemd-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>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 <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="opt" rep="repeat">VARIABLE=VALUE</arg></command>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><command>systemd-notify</command> may be called by daemon
    scripts to notify the init system 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 set for the service unit this command is called from.</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 PID 1 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.</para>

    <para><command>systemd-notify</command> will first attempt to invoke <function>sd_notify()</function> pretending to
    have the PID of 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> described above.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>

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

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

        <listitem><para>Inform the init system about service start-up
        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>--pid=</option></term>

        <listitem><para>Inform the init system about the main PID of
        the daemon. Takes a PID as argument. If the argument is
        omitted, the PID of the process that invoked
        <command>systemd-notify</command> is used. This 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></listitem>
      </varlistentry>

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

        <listitem><para>Send a free-form status string for the daemon
        to the init systemd. 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>.</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>

      <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/bash

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

while : ; do
        read 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>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>