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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 General Public License as published by
the Free Software Foundation; either version 2 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
General Public License for more details.
You should have received a copy of the GNU General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="sd-daemon">
<refentryinfo>
<title>sd-daemon</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-daemon</refentrytitle>
<manvolnum>7</manvolnum>
</refmeta>
<refnamediv>
<refname>sd-daemon</refname>
<refpurpose>Reference implementation of APIs for
new-style daemons</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo>
</funcsynopsis>
<cmdsynopsis>
<command>pkg-config --cflags --libs libsystemd-daemon</command>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>sd-daemon.c</filename> and
<filename>sd-daemon.h</filename> provide a reference
implementation of various APIs for new-style daemons,
as implemented by the
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
init system.</para>
<para>See
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for more information about the functions
implemented. In addition to these functions a couple
of logging prefixes are defined as macros:</para>
<programlisting>#define SD_EMERG "<0>" /* system is unusable */
#define SD_ALERT "<1>" /* action must be taken immediately */
#define SD_CRIT "<2>" /* critical conditions */
#define SD_ERR "<3>" /* error conditions */
#define SD_WARNING "<4>" /* warning conditions */
#define SD_NOTICE "<5>" /* normal but significant condition */
#define SD_INFO "<6>" /* informational */
#define SD_DEBUG "<7>" /* debug-level messages */</programlisting>
<para>These prefixes are intended to be used in
conjunction with STDERR-based logging as implemented
by systemd. If a systemd service definition file is
configured with <varname>StandardError=syslog</varname>
or <varname>StandardError=kmsg</varname> these
prefixes can be used to encode a log level in lines
printed. This is similar to the kernel
<function>printk()</function>-style logging. See
<citerefentry><refentrytitle>klogctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for more information.</para>
<para>The log levels are identical to
<citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s
log level system. To use these prefixes simply prefix
every line with one of these strings. A line that is
not prefixed will be logged at the default log level
SD_INFO.</para>
<example>
<title>Hello World</title>
<para>A daemon may log with the log level
NOTICE by issuing this call:</para>
<programlisting>fprintf(stderr, SD_NOTICE "Hello World!\n");</programlisting>
</example>
</refsect1>
<refsect1>
<title>Notes</title>
<para>These interfaces 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. See the respective function man pages
for details.</para>
<para>In addition, for details about the algorithms
check the liberally licensed reference implementation
sources:
<ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/sd-daemon.c"/>
resp. <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
<para>These APIs 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,
either verbatim or in excerpts.</para>
<para>The functions directly related to new-style
daemons become NOPs when -DDISABLE_SYSTEMD is set
during compilation and the reference implementation is
used as drop-in files. In addition, if
<filename>sd-daemon.c</filename> is compiled on
non-Linux systems they become NOPs.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-readahead</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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