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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" [
-<!ENTITY % entities SYSTEM "custom-entities.ent" >
-%entities;
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- This file is part of systemd.
-
- Copyright 2010 Lennart Poettering
-
- systemd is free software; you can redistribute it and/or modify it
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+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<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>
<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
+ 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
<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=all</varname> is
- set for the service unit this command is called from.</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. When <option>--no-block</option> is used, all 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>Hence, <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>. Use the <option>--pid=</option>
+ switch to tweak this behaviour.</para>
</refsect1>
<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=$PID</command>. For details
- about the semantics of this option see
+ <listitem><para>Inform the service manager about the main PID of the daemon. Takes a PID as
+ argument. If the argument is specified as <literal>auto</literal> or omitted, the PID of the process
+ that invoked <command>systemd-notify</command> is used, except if that's the service manager. If the
+ argument is specified as <literal>self</literal>, the PID of the <command>systemd-notify</command>
+ command itself is used, and if <literal>parent</literal> is specified the calling process' PID is
+ used — even if it is the service manager. This is equivalent to <command>systemd-notify
+ MAINPID=$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>--uid=</option><replaceable>USER</replaceable></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></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
+ STATUS=…</command>. For details about the semantics of this
option see
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
</varlistentry>
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>.</para></listitem>
+ <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></listitem>
</varlistentry>
<xi:include href="standard-options.xml" xpointer="help" />
<programlisting>#!/bin/bash
mkfifo /tmp/waldo
-systemd-notify --ready --status="Waiting for data..."
+systemd-notify --ready --status="Waiting for data…"
while : ; do
- read a < /tmp/waldo
- systemd-notify --status="Processing $a"
+ read a < /tmp/waldo
+ systemd-notify --status="Processing $a"
- # Do something with $a ...
+ # Do something with $a …
- systemd-notify --status="Waiting for data..."
+ systemd-notify --status="Waiting for data…"
done</programlisting>
</example>
</refsect1>
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