<?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">

<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>3</manvolnum>

</refmeta>

<refnamediv>

<refname>sd-daemon</refname>

<refname>SD_EMERG</refname>

<refname>SD_ALERT</refname>

<refname>SD_CRIT</refname>

<refname>SD_ERR</refname>

<refname>SD_WARNING</refname>

<refname>SD_NOTICE</refname>

<refname>SD_INFO</refname>

<refname>SD_DEBUG</refname>

<refpurpose>Reference implementation of APIs for

new-style daemons</refpurpose>

</refnamediv>

<refsynopsisdiv>

<funcsynopsis>

<funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</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 "&lt;0&gt;" /* system is unusable */

#define SD_ALERT "&lt;1&gt;" /* action must be taken immediately */

#define SD_CRIT "&lt;2&gt;" /* critical conditions */

#define SD_ERR "&lt;3&gt;" /* error conditions */

#define SD_WARNING "&lt;4&gt;" /* warning conditions */

#define SD_NOTICE "&lt;5&gt;" /* normal but significant condition */

#define SD_INFO "&lt;6&gt;" /* informational */

#define SD_DEBUG "&lt;7&gt;" /* 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/libsystemd-daemon/sd-daemon.c"/>

and <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

<constant>libsystemd-daemon</constant> <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>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>