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a9becdd65b
Systemd 209 started setting $WATCHDOG_PID, and sd-daemon watch was modified to check for this variable. This means that sd_watchdog_enabled() stopped working with previous versions of systemd. But sd-event is a public library and API and we must keep it working even when a program compiled with a newer version of the libary is used on a system running an older version of the manager. getenv() and unsetenv() are fairly expensive calls, so optimize sd_watchdog_enabled() by not calling them when unnecessary. man: centralize the description of $WATCHDOG_PID and $WATCHDOG_USEC in the sd_watchdog_enabled manpage. It is better not to repeat the same stuff in two places.
319 lines
15 KiB
XML
319 lines
15 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2010 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_notify"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_notify</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_notify</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_notify</refname>
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<refname>sd_notifyf</refname>
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<refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_notify</function></funcdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>const char *<parameter>state</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_notifyf</function></funcdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>const char *<parameter>format</parameter></paramdef>
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<paramdef>...</paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_notify()</function> may be called
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by a service to notify the service manager about
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state changes. It can be used to send arbitrary
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information, encoded in an environment-block-like
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string. Most importantly it can be used for start-up
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completion notification.</para>
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<para>If the <parameter>unset_environment</parameter>
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parameter is non-zero, <function>sd_notify()</function>
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will unset the <varname>$NOTIFY_SOCKET</varname>
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environment variable before returning (regardless of
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whether the function call itself succeeded or
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not). Further calls to
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<function>sd_notify()</function> will then fail, but
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the variable is no longer inherited by child
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processes.</para>
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<para>The <parameter>state</parameter> parameter
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should contain a newline-separated list of variable
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assignments, similar in style to an environment
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block. A trailing newline is implied if none is
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specified. The string may contain any kind of variable
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assignments, but the following shall be considered
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well-known:</para>
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<variablelist>
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<varlistentry>
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<term>READY=1</term>
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<listitem><para>Tells the service
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manager that service startup is
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finished. This is only used by systemd
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if the service definition file has
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Type=notify set. Since there is little
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value in signaling non-readiness, the
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only value services should send is
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<literal>READY=1</literal>
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(i.e. <literal>READY=0</literal> is
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not defined).</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>RELOADING=1</term>
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<listitem><para>Tells the service manager
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that the service is reloading its
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configuration. This is useful to allow
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the service manager to track the service's
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internal state, and present it to the
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user. Note that a service that sends
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this notification must also send a
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<literal>READY=1</literal>
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notification when it completed
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reloading its
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configuration.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>STOPPING=1</term>
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<listitem><para>Tells the service manager
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that the service is beginning its
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shutdown. This is useful to allow the
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service manager to track the service's
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internal state, and present it to the
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user.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>STATUS=...</term>
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<listitem><para>Passes a single-line
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UTF-8 status string back to the service manager
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that describes the service state. This
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is free-form and can be used for
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various purposes: general state
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feedback, fsck-like programs could
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pass completion percentages and
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failing programs could pass a human
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readable error message. Example:
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<literal>STATUS=Completed 66% of file
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system
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check...</literal></para></listitem>
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</varlistentry>
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<varlistentry>
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<term>ERRNO=...</term>
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<listitem><para>If a service fails, the
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errno-style error code, formatted as
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string. Example: <literal>ERRNO=2</literal> for
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ENOENT.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>BUSERROR=...</term>
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<listitem><para>If a service fails, the
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D-Bus error-style error code. Example:
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<literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
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</varlistentry>
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<varlistentry>
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<term>MAINPID=...</term>
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<listitem><para>The main pid of the
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service, in case the service manager did
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not fork off the process
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itself. Example:
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<literal>MAINPID=4711</literal></para></listitem>
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</varlistentry>
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<varlistentry>
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<term>WATCHDOG=1</term>
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<listitem><para>Tells systemd to
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update the watchdog timestamp. This is
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the keep-alive ping that services need
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to issue in regular intervals if
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<varname>WatchdogSec=</varname> is
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enabled for it. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for information how to enable this
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functionality and
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<citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for the details of how the service can
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check if the the watchdog is enabled.
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</para></listitem>
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</varlistentry>
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</variablelist>
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<para>It is recommended to prefix variable names that
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are not shown in the list above with
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<varname>X_</varname> to avoid namespace
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clashes.</para>
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<para>Note that systemd will accept status data sent
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from a service only if the
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<varname>NotifyAccess=</varname> option is correctly
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set in the service definition file. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details.</para>
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<para><function>sd_notifyf()</function> is similar to
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<function>sd_notify()</function> but takes a
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<function>printf()</function>-like format string plus
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arguments.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On failure, these calls return a negative
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errno-style error code. If
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<varname>$NOTIFY_SOCKET</varname> was not set and
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hence no status data could be sent, 0 is returned. If
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the status was sent, these functions return with a
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positive return value. In order to support both, init
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systems that implement this scheme and those which
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do not, it is generally recommended to ignore the return
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value of this call.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
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<para>Internally, these functions send a single
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datagram with the state string as payload to the
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<constant>AF_UNIX</constant> socket referenced in the
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<varname>$NOTIFY_SOCKET</varname> environment
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variable. If the first character of
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<varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the string is
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understood as Linux abstract namespace socket. The
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datagram is accompanied by the process credentials of
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the sending service, using SCM_CREDENTIALS.</para>
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</refsect1>
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<refsect1>
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<title>Environment</title>
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<variablelist class='environment-variables'>
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<varlistentry>
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<term><varname>$NOTIFY_SOCKET</varname></term>
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<listitem><para>Set by the service manager
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for supervised processes for status
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and start-up completion
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notification. This environment variable
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specifies the socket
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<function>sd_notify()</function> talks
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to. See above for details.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<example>
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<title>Start-up Notification</title>
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<para>When a service finished starting up, it
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might issue the following call to notify
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the service manager:</para>
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<programlisting>sd_notify(0, "READY=1");</programlisting>
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</example>
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<example>
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<title>Extended Start-up Notification</title>
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<para>A service could send the following after
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completing initialization:</para>
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<programlisting>sd_notifyf(0, "READY=1\n"
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"STATUS=Processing requests...\n"
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"MAINPID=%lu",
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(unsigned long) getpid());</programlisting>
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</example>
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<example>
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<title>Error Cause Notification</title>
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<para>A service could send the following shortly before exiting, on failure</para>
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<programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
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"ERRNO=%i",
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strerror(errno),
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errno);</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>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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