man/systemd-notify.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="systemd-notify"
   7     xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>systemd-notify</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>systemd-notify</refentrytitle>
  16     <manvolnum>1</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>systemd-notify</refname>
  21     <refpurpose>Notify service manager about start-up completion and other daemon status changes</refpurpose>
  22   </refnamediv>
  23
  24   <refsynopsisdiv>
  25     <cmdsynopsis>
  26       <command>systemd-notify <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="opt" rep="repeat">VARIABLE=VALUE</arg></command>
  27     </cmdsynopsis>
  28   </refsynopsisdiv>
  29
  30   <refsect1>
  31     <title>Description</title>
  32
  33     <para><command>systemd-notify</command> may be called by daemon
  34     scripts to notify the init system about status changes. It can be
  35     used to send arbitrary information, encoded in an
  36     environment-block-like list of strings. Most importantly, it can be
  37     used for start-up completion notification.</para>
  38
  39     <para>This is mostly just a wrapper around
  40     <function>sd_notify()</function> and makes this functionality
  41     available to shell scripts. For details see
  42     <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  43     </para>
  44
  45     <para>The command line may carry a list of environment variables
  46     to send as part of the status update.</para>
  47
  48     <para>Note that systemd will refuse reception of status updates from this command unless
  49     <varname>NotifyAccess=</varname> is set for the service unit this command is called from.</para>
  50
  51     <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
  52     the sending process is still around at the time PID 1 processes the message, or if the sending process is
  53     explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
  54     off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
  55     <varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
  56     <function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
  57     attribute the message to the unit, and thus will ignore it, even if <varname>NotifyAccess=</varname><option>all
  58     </option> is set for it. When <option>--no-block</option> is used, all synchronization for reception of notifications
  59     is disabled, and hence the aforementioned race may occur if the invoking process is not the service manager or spawned
  60     by the service manager.</para>
  61
  62     <para>Hence, <command>systemd-notify</command> will first attempt to invoke <function>sd_notify()</function>
  63     pretending to have the PID of the invoking process. This will only succeed when invoked with sufficient privileges.
  64     On failure, it will then fall back to invoking it under its own PID. This behaviour is useful in order that when
  65     the tool is invoked from a shell script the shell process — and not the <command>systemd-notify</command> process
  66     — appears as sender of the message, which in turn is helpful if the shell process is the main process of a service,
  67     due to the limitations of <varname>NotifyAccess=</varname><option>all</option>. Use the <option>--pid=</option>
  68     switch to tweak this behaviour.</para>
  69
  70   </refsect1>
  71
  72   <refsect1>
  73     <title>Options</title>
  74
  75     <para>The following options are understood:</para>
  76
  77     <variablelist>
  78       <varlistentry>
  79         <term><option>--ready</option></term>
  80
  81         <listitem><para>Inform the init system about service start-up
  82         completion. This is equivalent to <command>systemd-notify
  83         READY=1</command>. For details about the semantics of this
  84         option see
  85         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
  86       </varlistentry>
  87
  88       <varlistentry>
  89         <term><option>--pid=</option></term>
  90
  91         <listitem><para>Inform the service manager about the main PID of the daemon. Takes a PID as
  92         argument. If the argument is specified as <literal>auto</literal> or omitted, the PID of the process
  93         that invoked <command>systemd-notify</command> is used, except if that's the service manager. If the
  94         argument is specified as <literal>self</literal>, the PID of the <command>systemd-notify</command>
  95         command itself is used, and if <literal>parent</literal> is specified the calling process' PID is
  96         used — even if it is the service manager. This is equivalent to <command>systemd-notify
  97         MAINPID=$PID</command>. For details about the semantics of this option see
  98         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
  99       </varlistentry>
 100
 101       <varlistentry>
 102         <term><option>--uid=</option><replaceable>USER</replaceable></term>
 103
 104         <listitem><para>Set the user ID to send the notification from. Takes a UNIX user name or numeric UID. When
 105         specified the notification message will be sent with the specified UID as sender, in place of the user the
 106         command was invoked as. This option requires sufficient privileges in order to be able manipulate the user
 107         identity of the process.</para></listitem>
 108       </varlistentry>
 109
 110       <varlistentry>
 111         <term><option>--status=</option></term>
 112
 113         <listitem><para>Send a free-form status string for the daemon
 114         to the init systemd. This option takes the status string as
 115         argument. This is equivalent to <command>systemd-notify
 116         STATUS=…</command>. For details about the semantics of this
 117         option see
 118         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 119       </varlistentry>
 120
 121       <varlistentry>
 122         <term><option>--booted</option></term>
 123
 124         <listitem><para>Returns 0 if the system was booted up with
 125         systemd, non-zero otherwise. If this option is passed, no
 126         message is sent. This option is hence unrelated to the other
 127         options. For details about the semantics of this option, see
 128         <citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>. An
 129         alternate way to check for this state is to call
 130         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 131         with the <command>is-system-running</command> command. It will
 132         return <literal>offline</literal> if the system was not booted
 133         with systemd.  </para></listitem>
 134       </varlistentry>
 135
 136       <varlistentry>
 137         <term><option>--no-block</option></term>
 138
 139         <listitem><para>Do not synchronously wait for the requested operation to finish.
 140         Use of this option is only recommended when <command>systemd-notify</command>
 141         is spawned by the service manager, or when the invoking process is directly spawned
 142         by the service manager and has enough privileges to allow <command>systemd-notify
 143         </command> to send the notification on its behalf. Sending notifications with
 144         this option set is prone to race conditions in all other cases.</para></listitem>
 145       </varlistentry>
 146
 147       <xi:include href="standard-options.xml" xpointer="help" />
 148       <xi:include href="standard-options.xml" xpointer="version" />
 149     </variablelist>
 150
 151   </refsect1>
 152
 153   <refsect1>
 154     <title>Exit status</title>
 155
 156     <para>On success, 0 is returned, a non-zero failure code
 157     otherwise.</para>
 158   </refsect1>
 159
 160   <refsect1>
 161     <title>Example</title>
 162
 163     <example>
 164       <title>Start-up Notification and Status Updates</title>
 165
 166       <para>A simple shell daemon that sends start-up notifications
 167       after having set up its communication channel. During runtime it
 168       sends further status updates to the init system:</para>
 169
 170       <programlisting>#!/bin/bash
 171
 172 mkfifo /tmp/waldo
 173 systemd-notify --ready --status="Waiting for data…"
 174
 175 while : ; do
 176         read a &lt; /tmp/waldo
 177         systemd-notify --status="Processing $a"
 178
 179         # Do something with $a …
 180
 181         systemd-notify --status="Waiting for data…"
 182 done</programlisting>
 183     </example>
 184   </refsect1>
 185
 186   <refsect1>
 187     <title>See Also</title>
 188     <para>
 189       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 190       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 191       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 192       <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 193       <citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 194     </para>
 195   </refsect1>
 196
 197 </refentry>