man/systemd-notify.xml

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   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-or-later -->
   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     <cmdsynopsis>
  29       <command>systemd-notify --exec <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="opt" rep="repeat">VARIABLE=VALUE</arg> ; <arg rep="repeat">CMDLINE</arg></command>
  30     </cmdsynopsis>
  31   </refsynopsisdiv>
  32
  33   <refsect1>
  34     <title>Description</title>
  35
  36     <para><command>systemd-notify</command> may be called by service scripts to notify the invoking service
  37     manager about status changes. It can be used to send arbitrary information, encoded in an
  38     environment-block-like list of strings. Most importantly, it can be used for start-up completion
  39     notification.</para>
  40
  41     <para>This is mostly just a wrapper around <function>sd_notify()</function> and makes this functionality
  42     available to shell scripts. For details see
  43     <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  44     </para>
  45
  46     <para>The command line may carry a list of environment variables to send as part of the status
  47     update.</para>
  48
  49     <para>Note that systemd will refuse reception of status updates from this command unless
  50     <varname>NotifyAccess=</varname> is appropriately set for the service unit this command is called
  51     from. See
  52     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
  53     details.</para>
  54
  55     <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only
  56     if either the sending process is still around at the time the service manager processes the message, or
  57     if the sending process is explicitly runtime-tracked by the service manager. The latter is the case if
  58     the service manager originally forked off the process, i.e. on all processes that match
  59     <varname>NotifyAccess=</varname><option>main</option> or
  60     <varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit
  61     sends an <function>sd_notify()</function> message and immediately exits, the service manager might not be
  62     able to properly attribute the message to the unit, and thus will ignore it, even if
  63     <varname>NotifyAccess=</varname><option>all</option> is set for it. To address this
  64     <command>systemd-notify</command> will wait until the notification message has been processed by the
  65     service manager. When <option>--no-block</option> is used, this synchronization for reception of
  66     notifications is disabled, and hence the aforementioned race may occur if the invoking process is not the
  67     service manager or spawned by the service manager.</para>
  68
  69     <para><command>systemd-notify</command> will first attempt to invoke <function>sd_notify()</function>
  70     pretending to have the PID of the parent process of <command>systemd-notify</command> (i.e. the invoking
  71     process). This will only succeed when invoked with sufficient privileges.  On failure, it will then fall
  72     back to invoking it under its own PID. This behaviour is useful in order that when the tool is invoked
  73     from a shell script the shell process — and not the <command>systemd-notify</command> process — appears
  74     as sender of the message, which in turn is helpful if the shell process is the main process of a service,
  75     due to the limitations of <varname>NotifyAccess=</varname><option>all</option>. Use the
  76     <option>--pid=</option> switch to tweak this behaviour.</para>
  77   </refsect1>
  78
  79   <refsect1>
  80     <title>Options</title>
  81
  82     <para>The following options are understood:</para>
  83
  84     <variablelist>
  85       <varlistentry>
  86         <term><option>--ready</option></term>
  87
  88         <listitem><para>Inform the invoking service manager about service start-up or configuration reload
  89         completion. This is equivalent to <command>systemd-notify READY=1</command>. For details about the
  90         semantics of this option see
  91         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
  92       </varlistentry>
  93
  94       <varlistentry>
  95         <term><option>--reloading</option></term>
  96
  97         <listitem><para>Inform the invoking service manager about the beginning of a configuration reload
  98         cycle. This is equivalent to <command>systemd-notify RELOADING=1</command> (but implicitly also sets
  99         a <varname>MONOTONIC_USEC=</varname> field as required for <varname>Type=notify-reload</varname>
 100         services, see
 101         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 102         for details). For details about the semantics of this option see
 103         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 104
 105         <xi:include href="version-info.xml" xpointer="v253"/></listitem>
 106       </varlistentry>
 107
 108       <varlistentry>
 109         <term><option>--stopping</option></term>
 110
 111         <listitem><para>Inform the invoking service manager about the beginning of the shutdown phase of the
 112         service. This is equivalent to <command>systemd-notify STOPPING=1</command>. For details about the
 113         semantics of this option see
 114         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 115
 116         <xi:include href="version-info.xml" xpointer="v253"/></listitem>
 117       </varlistentry>
 118
 119       <varlistentry>
 120         <term><option>--pid=</option></term>
 121
 122         <listitem><para>Inform the service manager about the main PID of the service. Takes a PID as
 123         argument. If the argument is specified as <literal>auto</literal> or omitted, the PID of the process
 124         that invoked <command>systemd-notify</command> is used, except if that's the service manager. If the
 125         argument is specified as <literal>self</literal>, the PID of the <command>systemd-notify</command>
 126         command itself is used, and if <literal>parent</literal> is specified the calling process' PID is
 127         used — even if it is the service manager. The latter is equivalent to <command>systemd-notify
 128         MAINPID=$PID</command>. For details about the semantics of this option see
 129         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 130
 131         <para>If this switch is used in an <command>systemd-notify</command> invocation from a process that
 132         shall become the new main process of a service — and which is not the process forked off by the
 133         service manager (or the current main process) —, then it is essential to set
 134         <varname>NotifyAccess=all</varname> in the service unit file, or otherwise the notification will be
 135         ignored for security reasons. See
 136         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 137         for details.</para></listitem>
 138       </varlistentry>
 139
 140       <varlistentry>
 141         <term><option>--uid=</option><replaceable>USER</replaceable></term>
 142
 143         <listitem><para>Set the user ID to send the notification from. Takes a UNIX user name or numeric UID. When
 144         specified the notification message will be sent with the specified UID as sender, in place of the user the
 145         command was invoked as. This option requires sufficient privileges in order to be able manipulate the user
 146         identity of the process.</para>
 147
 148         <xi:include href="version-info.xml" xpointer="v237"/></listitem>
 149       </varlistentry>
 150
 151       <varlistentry>
 152         <term><option>--status=</option></term>
 153
 154         <listitem><para>Send a free-form human readable status string for the daemon to the service
 155         manager. This option takes the status string as argument. This is equivalent to
 156         <command>systemd-notify STATUS=…</command>. For details about the semantics of this option see
 157         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This
 158         information is shown in
 159         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 160         <command>status</command> output, among other places.</para></listitem>
 161       </varlistentry>
 162
 163       <varlistentry>
 164         <term><option>--booted</option></term>
 165
 166         <listitem><para>Returns 0 if the system was booted up with systemd, non-zero otherwise. If this
 167         option is passed, no message is sent. This option is hence unrelated to the other options. For
 168         details about the semantics of this option, see
 169         <citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>. An
 170         alternate way to check for this state is to call
 171         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> with
 172         the <command>is-system-running</command> command. It will return <literal>offline</literal> if the
 173         system was not booted with systemd.  </para></listitem>
 174       </varlistentry>
 175
 176       <varlistentry>
 177         <term><option>--no-block</option></term>
 178
 179         <listitem><para>Do not synchronously wait for the requested operation to finish.  Use of this option
 180         is only recommended when <command>systemd-notify</command> is spawned by the service manager, or when
 181         the invoking process is directly spawned by the service manager and has enough privileges to allow
 182         <command>systemd-notify</command> to send the notification on its behalf. Sending notifications with
 183         this option set is prone to race conditions in all other cases.</para>
 184
 185         <xi:include href="version-info.xml" xpointer="v246"/></listitem>
 186       </varlistentry>
 187
 188       <varlistentry>
 189         <term><option>--exec</option></term>
 190
 191         <listitem><para>If specified <command>systemd-notify</command> will execute another command line
 192         after it completed its operation, replacing its own process. If used, the list of assignments to
 193         include in the message sent must be followed by a <literal>;</literal> character (as separate
 194         argument), followed by the command line to execute. This permits "chaining" of commands, i.e. issuing
 195         one operation, followed immediately by another, without changing PIDs.</para>
 196
 197         <para>Note that many shells interpret <literal>;</literal> as their own separator for command lines,
 198         hence when <command>systemd-notify</command> is invoked from a shell the semicolon must usually be
 199         escaped as <literal>\;</literal>.</para>
 200
 201         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 202       </varlistentry>
 203
 204       <varlistentry>
 205         <term><option>--fd=</option></term>
 206
 207         <listitem><para>Send a file descriptor along with the notification message. This is useful when
 208         invoked in services that have the <varname>FileDescriptorStoreMax=</varname> setting enabled, see
 209         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 210         for details. The specified file descriptor must be passed to <command>systemd-notify</command> when
 211         invoked. This option may be used multiple times to pass multiple file descriptors in a single
 212         notification message.</para>
 213
 214         <para>To use this functionality from a <command>bash</command> shell, use an expression like the following:</para>
 215         <programlisting>systemd-notify --fd=4 --fd=5 4&lt;/some/file 5&lt;/some/other/file</programlisting>
 216
 217         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 218       </varlistentry>
 219
 220       <varlistentry>
 221         <term><option>--fdname=</option></term>
 222
 223         <listitem><para>Set a name to assign to the file descriptors passed via <option>--fd=</option> (see
 224         above). This controls the <literal>FDNAME=</literal> field. This setting may only be specified once,
 225         and applies to all file descriptors passed. Invoke this tool multiple times in case multiple file
 226         descriptors with different file descriptor names shall be submitted.</para>
 227
 228         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 229       </varlistentry>
 230
 231       <xi:include href="standard-options.xml" xpointer="help" />
 232       <xi:include href="standard-options.xml" xpointer="version" />
 233     </variablelist>
 234
 235   </refsect1>
 236
 237   <refsect1>
 238     <title>Exit status</title>
 239
 240     <para>On success, 0 is returned, a non-zero failure code
 241     otherwise.</para>
 242   </refsect1>
 243
 244   <refsect1>
 245     <title>Example</title>
 246
 247     <example>
 248       <title>Start-up Notification and Status Updates</title>
 249
 250       <para>A simple shell daemon that sends start-up notifications after having set up its communication
 251       channel. During runtime it sends further status updates to the init system:</para>
 252
 253       <programlisting>#!/bin/sh
 254
 255 mkfifo /tmp/waldo
 256 systemd-notify --ready --status="Waiting for data…"
 257
 258 while : ; do
 259         read -r a &lt; /tmp/waldo
 260         systemd-notify --status="Processing $a"
 261
 262         # Do something with $a …
 263
 264         systemd-notify --status="Waiting for data…"
 265 done</programlisting>
 266     </example>
 267   </refsect1>
 268
 269   <refsect1>
 270     <title>See Also</title>
 271     <para>
 272       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 273       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 274       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 275       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 276       <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 277       <citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 278     </para>
 279   </refsect1>
 280 </refentry>