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320 lines
15 KiB
XML
320 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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<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 init system about start-up completion and other daemon 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> shall be called
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by a daemon to notify the init system about status
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changes. It can be used to send arbitrary information,
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encoded in an environment-block-like string. Most
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importantly it can be used for start-up completion
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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
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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 an 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 init system
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that daemon startup is finished. This
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is only used by systemd if the service
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definition file has Type=notify
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set. The passed argument is a boolean
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"1" or "0". Since there is little
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value in signalling non-readiness, the
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only value daemons should send is
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"READY=1".</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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status string back to the init system
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that describes the daemon 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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"STATUS=Completed 66% of file system
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check..."</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 daemon fails, the
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errno-style error code, formatted as
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string. Example: "ERRNO=2" 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 daemon fails, the
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D-Bus error-style error code. Example:
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"BUSERROR=org.freedesktop.DBus.Error.TimedOut"</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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daemon, in case the init system did
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not fork off the process
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itself. Example:
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"MAINPID=4711"</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 details. It is recommended to send
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this message if the
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<varname>WATCHDOG_USEC=</varname>
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environment variable has been set for
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the service process, in every half the
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time interval that is specified in the
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variable.</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 daemon 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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don't, 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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<para>These functions are provided by the reference
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implementation of APIs for new-style daemons and
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distributed with the systemd package. The algorithms
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they implement are simple, and can easily be
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reimplemented in daemons if it is important to support
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this interface without using the reference
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implementation.</para>
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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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AF_UNIX 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 @ 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 daemon, using SCM_CREDENTIALS.</para>
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<para>For details about the algorithms check the
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liberally licensed reference implementation sources:
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<ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/sd-daemon.c"/>
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resp. <ulink
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url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
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<para><function>sd_notify()</function> and
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<function>sd_notifyf()</function> are implemented in
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the reference implementation's
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<filename>sd-daemon.c</filename> and
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<filename>sd-daemon.h</filename> files. These
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interfaces are available as shared library, which can
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be compiled and linked to with the
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<literal>libsystemd-daemon</literal>
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<citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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file. Alternatively, applications consuming these APIs
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may copy the implementation into their source tree. For
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more details about the reference implementation see
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<citerefentry><refentrytitle>sd_daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
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<para>If the reference implementation is used as
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drop-in files and -DDISABLE_SYSTEMD is set during
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compilation these functions will always return 0 and
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otherwise become a NOP.</para>
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</refsect1>
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<refsect1>
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<title>Environment</title>
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<variablelist>
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<varlistentry>
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<term><varname>$NOTIFY_SOCKET</varname></term>
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<listitem><para>Set by the init system
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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 daemon finished starting up, it
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might issue the following call to notify
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the init system:</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 daemon 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 daemon 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>7</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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</para>
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</refsect1>
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</refentry>
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