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https://github.com/AuxXxilium/eudev.git
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5430f7f2bc
We finally got the OK from all contributors with non-trivial commits to relicense systemd from GPL2+ to LGPL2.1+. Some udev bits continue to be GPL2+ for now, but we are looking into relicensing them too, to allow free copy/paste of all code within systemd. The bits that used to be MIT continue to be MIT. The big benefit of the relicensing is that closed source code may now link against libsystemd-login.so and friends.
313 lines
14 KiB
XML
313 lines
14 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.
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Services using this feature should do
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this in regular intervals. A watchdog
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framework can use the timestamps to
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detect failed
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services.</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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