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https://github.com/systemd/systemd-stable.git
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5ec7a9947e
Add note for change of behaviour in systemd-notify, where parent pid trick is only used when --no-block is passed, and with enough privileges ofcourse. Also, fix a small error in systemd(1).
198 lines
9.0 KiB
XML
198 lines
9.0 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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<refentry id="systemd-notify"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>systemd-notify</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-notify</refentrytitle>
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<manvolnum>1</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-notify</refname>
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<refpurpose>Notify service manager about start-up completion and other daemon status changes</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>systemd-notify <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="opt" rep="repeat">VARIABLE=VALUE</arg></command>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><command>systemd-notify</command> may be called by daemon
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scripts to notify the init system about status changes. It can be
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used to send arbitrary information, encoded in an
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environment-block-like list of strings. Most importantly, it can be
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used for start-up completion notification.</para>
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<para>This is mostly just a wrapper around
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<function>sd_notify()</function> and makes this functionality
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available to shell scripts. For details see
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<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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</para>
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<para>The command line may carry a list of environment variables
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to send as part of the status update.</para>
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<para>Note that systemd will refuse reception of status updates from this command unless
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<varname>NotifyAccess=</varname> is set for the service unit this command is called from.</para>
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<para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
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the sending process is still around at the time PID 1 processes the message, or if the sending process is
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explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
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off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
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<varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
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<function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
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attribute the message to the unit, and thus will ignore it, even if <varname>NotifyAccess=</varname><option>all
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</option> is set for it. When <option>--no-block</option> is used, all synchronization for reception of notifications
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is disabled, and hence the aforementioned race may occur if the invoking process is not the service manager or spawned
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by the service manager.</para>
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<para>Hence, <command>systemd-notify</command> will first attempt to invoke <function>sd_notify()</function>
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pretending to have the PID of the invoking process. This will only succeed when invoked with sufficient privileges.
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On failure, it will then fall back to invoking it under its own PID. This behaviour is useful in order that when
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the tool is invoked from a shell script the shell process — and not the <command>systemd-notify</command> process
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— appears as sender of the message, which in turn is helpful if the shell process is the main process of a service,
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due to the limitations of <varname>NotifyAccess=</varname><option>all</option>. Use the <option>--pid=</option>
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switch to tweak this behaviour.</para>
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</refsect1>
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<refsect1>
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<title>Options</title>
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<para>The following options are understood:</para>
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<variablelist>
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<varlistentry>
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<term><option>--ready</option></term>
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<listitem><para>Inform the init system about service start-up
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completion. This is equivalent to <command>systemd-notify
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READY=1</command>. For details about the semantics of this
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option see
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<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--pid=</option></term>
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<listitem><para>Inform the service manager about the main PID of the daemon. Takes a PID as
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argument. If the argument is specified as <literal>auto</literal> or omitted, the PID of the process
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that invoked <command>systemd-notify</command> is used, except if that's the service manager. If the
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argument is specified as <literal>self</literal>, the PID of the <command>systemd-notify</command>
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command itself is used, and if <literal>parent</literal> is specified the calling process' PID is
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used — even if it is the service manager. This is equivalent to <command>systemd-notify
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MAINPID=$PID</command>. For details about the semantics of this option see
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<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--uid=</option><replaceable>USER</replaceable></term>
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<listitem><para>Set the user ID to send the notification from. Takes a UNIX user name or numeric UID. When
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specified the notification message will be sent with the specified UID as sender, in place of the user the
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command was invoked as. This option requires sufficient privileges in order to be able manipulate the user
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identity of the process.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--status=</option></term>
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<listitem><para>Send a free-form status string for the daemon
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to the init systemd. This option takes the status string as
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argument. This is equivalent to <command>systemd-notify
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STATUS=…</command>. For details about the semantics of this
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option see
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<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--booted</option></term>
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<listitem><para>Returns 0 if the system was booted up with
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systemd, non-zero otherwise. If this option is passed, no
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message is sent. This option is hence unrelated to the other
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options. For details about the semantics of this option, see
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<citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>. An
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alternate way to check for this state is to call
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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with the <command>is-system-running</command> command. It will
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return <literal>offline</literal> if the system was not booted
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with systemd. </para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--no-block</option></term>
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<listitem><para>Do not synchronously wait for the requested operation to finish.
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Use of this option is only recommended when <command>systemd-notify</command>
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is spawned by the service manager, or when the invoking process is directly spawned
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by the service manager and has enough privileges to allow <command>systemd-notify
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</command> to send the notification on its behalf. Sending notifications with
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this option set is prone to race conditions in all other cases.</para></listitem>
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</varlistentry>
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<xi:include href="standard-options.xml" xpointer="help" />
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<xi:include href="standard-options.xml" xpointer="version" />
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Exit status</title>
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<para>On success, 0 is returned, a non-zero failure code
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otherwise.</para>
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</refsect1>
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<refsect1>
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<title>Example</title>
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<example>
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<title>Start-up Notification and Status Updates</title>
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<para>A simple shell daemon that sends start-up notifications
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after having set up its communication channel. During runtime it
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sends further status updates to the init system:</para>
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<programlisting>#!/bin/bash
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mkfifo /tmp/waldo
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systemd-notify --ready --status="Waiting for data…"
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while : ; do
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read a < /tmp/waldo
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systemd-notify --status="Processing $a"
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# Do something with $a …
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systemd-notify --status="Waiting for data…"
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done</programlisting>
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</example>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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