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