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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2010 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="sd_notify">
<refentryinfo>
<title>sd_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>
<refentrytitle>sd_notify</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_notify</refname>
<refname>sd_notifyf</refname>
<refpurpose>Notify service manager about start-up completion and other daemon status changes</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_notify</function></funcdef>
<paramdef>int <parameter>unset_environment</parameter></paramdef>
<paramdef>const char *<parameter>state</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_notifyf</function></funcdef>
<paramdef>int <parameter>unset_environment</parameter></paramdef>
<paramdef>const char *<parameter>format</parameter></paramdef>
<paramdef>...</paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_notify()</function> shall be called
by a daemon to notify the init system about status
changes. It can be used to send arbitrary information,
encoded in an environment-block-like string. Most
importantly it can be used for start-up completion
notification.</para>
<para>If the <parameter>unset_environment</parameter>
parameter is non-zero <function>sd_notify()</function>
will unset the <varname>$NOTIFY_SOCKET</varname>
environment variable before returning (regardless
whether the function call itself succeeded or
not). Further calls to
<function>sd_notify()</function> will then fail, but
the variable is no longer inherited by child
processes.</para>
<para>The <parameter>state</parameter> parameter
should contain an newline-separated list of variable
assignments, similar in style to an environment
block. A trailing newline is implied if none is
specified. The string may contain any kind of variable
assignments, but the following shall be considered
well-known:</para>
<variablelist>
<varlistentry>
<term>READY=1</term>
<listitem><para>Tells the init system
that daemon startup is finished. This
is only used by systemd if the service
definition file has Type=notify
set. The passed argument is a boolean
"1" or "0". Since there is little
value in signalling non-readiness, the
only value daemons should send is
"READY=1".</para></listitem>
</varlistentry>
<varlistentry>
<term>STATUS=...</term>
<listitem><para>Passes a single-line
status string back to the init system
that describes the daemon state. This
is free-form and can be used for
various purposes: general state
feedback, fsck-like programs could
pass completion percentages and
failing programs could pass a human
readable error message. Example:
"STATUS=Completed 66% of file system
check..."</para></listitem>
</varlistentry>
<varlistentry>
<term>ERRNO=...</term>
<listitem><para>If a daemon fails, the
errno-style error code, formatted as
string. Example: "ERRNO=2" for
ENOENT.</para></listitem>
</varlistentry>
<varlistentry>
<term>BUSERROR=...</term>
<listitem><para>If a daemon fails, the
D-Bus error-style error code. Example:
"BUSERROR=org.freedesktop.DBus.Error.TimedOut"</para></listitem>
</varlistentry>
<varlistentry>
<term>MAINPID=...</term>
<listitem><para>The main pid of the
daemon, in case the init system did
not fork off the process
itself. Example:
"MAINPID=4711"</para></listitem>
</varlistentry>
<varlistentry>
<term>WATCHDOG=1</term>
<listitem><para>Tells systemd to
update the watchdog timestamp. This is
the keep-alive ping that services need
to issue in regular intervals if
<varname>WatchdogSec=</varname> is
enabled for it. See
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details. It is recommended to send
this message if the
<varname>WATCHDOG_USEC=</varname>
environment variable has been set for
the service process, in every half the
time interval that is specified in the
variable.</para></listitem>
</varlistentry>
</variablelist>
<para>It is recommended to prefix variable names that
are not shown in the list above with
<varname>X_</varname> to avoid namespace
clashes.</para>
<para>Note that systemd will accept status data sent
from a daemon only if the
<varname>NotifyAccess=</varname> option is correctly
set in the service definition file. See
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details.</para>
<para><function>sd_notifyf()</function> is similar to
<function>sd_notify()</function> but takes a
<function>printf()</function>-like format string plus
arguments.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>On failure, these calls return a negative
errno-style error code. If
<varname>$NOTIFY_SOCKET</varname> was not set and
hence no status data could be sent, 0 is returned. If
the status was sent these functions return with a
positive return value. In order to support both, init
systems that implement this scheme and those which
don't, it is generally recommended to ignore the return
value of this call.</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>These functions are provided by the reference
implementation of APIs for new-style daemons and
distributed with the systemd package. The algorithms
they implement are simple, and can easily be
reimplemented in daemons if it is important to support
this interface without using the reference
implementation.</para>
<para>Internally, these functions send a single
datagram with the state string as payload to the
AF_UNIX socket referenced in the
<varname>$NOTIFY_SOCKET</varname> environment
variable. If the first character of
<varname>$NOTIFY_SOCKET</varname> is @ the string is
understood as Linux abstract namespace socket. The
datagram is accompanied by the process credentials of
the sending daemon, using SCM_CREDENTIALS.</para>
<para>For details about the algorithms check the
liberally licensed reference implementation sources:
<ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c"/>
resp. <ulink
url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
<para><function>sd_notify()</function> and
<function>sd_notifyf()</function> are implemented in
the reference implementation's
<filename>sd-daemon.c</filename> and
<filename>sd-daemon.h</filename> files. These
interfaces are available as shared library, which can
be compiled and linked to with the
<literal>libsystemd-daemon</literal>
<citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
file. Alternatively, applications consuming these APIs
may copy the implementation into their source tree. For
more details about the reference implementation see
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
<para>If the reference implementation is used as
drop-in files and -DDISABLE_SYSTEMD is set during
compilation these functions will always return 0 and
otherwise become a NOP.</para>
</refsect1>
<refsect1>
<title>Environment</title>
<variablelist>
<varlistentry>
<term><varname>$NOTIFY_SOCKET</varname></term>
<listitem><para>Set by the init system
for supervised processes for status
and start-up completion
notification. This environment variable
specifies the socket
<function>sd_notify()</function> talks
to. See above for details.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Examples</title>
<example>
<title>Start-up Notification</title>
<para>When a daemon finished starting up, it
might issue the following call to notify
the init system:</para>
<programlisting>sd_notify(0, "READY=1");</programlisting>
</example>
<example>
<title>Extended Start-up Notification</title>
<para>A daemon could send the following after
completing initialization:</para>
<programlisting>sd_notifyf(0, "READY=1\n"
"STATUS=Processing requests...\n"
"MAINPID=%lu",
(unsigned long) getpid());</programlisting>
</example>
<example>
<title>Error Cause Notification</title>
<para>A daemon could send the following shortly before exiting, on failure</para>
<programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
"ERRNO=%i",
strerror(errno),
errno);</programlisting>
</example>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
|
