man/sd-daemon.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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   8   Copyright 2010 Lennart Poettering
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  23
  24 <refentry id="sd-daemon">
  25
  26         <refentryinfo>
  27                 <title>sd-daemon</title>
  28                 <productname>systemd</productname>
  29
  30                 <authorgroup>
  31                         <author>
  32                                 <contrib>Developer</contrib>
  33                                 <firstname>Lennart</firstname>
  34                                 <surname>Poettering</surname>
  35                                 <email>lennart@poettering.net</email>
  36                         </author>
  37                 </authorgroup>
  38         </refentryinfo>
  39
  40         <refmeta>
  41                 <refentrytitle>sd-daemon</refentrytitle>
  42                 <manvolnum>3</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>sd-daemon</refname>
  47                 <refpurpose>Reference implementation of APIs for
  48                 new-style daemons</refpurpose>
  49         </refnamediv>
  50
  51         <refsynopsisdiv>
  52                 <funcsynopsis>
  53                         <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
  54                 </funcsynopsis>
  55
  56                 <cmdsynopsis>
  57                         <command>pkg-config --cflags --libs libsystemd-daemon</command>
  58                 </cmdsynopsis>
  59
  60         </refsynopsisdiv>
  61
  62         <refsect1>
  63                 <title>Description</title>
  64
  65                 <para><filename>sd-daemon.c</filename> and
  66                 <filename>sd-daemon.h</filename> provide a reference
  67                 implementation of various APIs for new-style daemons,
  68                 as implemented by the
  69                 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  70                 init system.</para>
  71
  72                 <para>See
  73                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  74                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  75                 <citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  76                 <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  77                 for more information about the functions
  78                 implemented. In addition to these functions a couple
  79                 of logging prefixes are defined as macros:</para>
  80
  81                 <programlisting>#define SD_EMERG   "&lt;0&gt;"  /* system is unusable */
  82 #define SD_ALERT   "&lt;1&gt;"  /* action must be taken immediately */
  83 #define SD_CRIT    "&lt;2&gt;"  /* critical conditions */
  84 #define SD_ERR     "&lt;3&gt;"  /* error conditions */
  85 #define SD_WARNING "&lt;4&gt;"  /* warning conditions */
  86 #define SD_NOTICE  "&lt;5&gt;"  /* normal but significant condition */
  87 #define SD_INFO    "&lt;6&gt;"  /* informational */
  88 #define SD_DEBUG   "&lt;7&gt;"  /* debug-level messages */</programlisting>
  89
  90                 <para>These prefixes are intended to be used in
  91                 conjunction with STDERR-based logging as implemented
  92                 by systemd. If a systemd service definition file is
  93                 configured with <varname>StandardError=syslog</varname>
  94                 or <varname>StandardError=kmsg</varname> these
  95                 prefixes can be used to encode a log level in lines
  96                 printed. This is similar to the kernel
  97                 <function>printk()</function>-style logging. See
  98                 <citerefentry><refentrytitle>klogctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
  99                 for more information.</para>
 100
 101                 <para>The log levels are identical to
 102                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s
 103                 log level system. To use these prefixes simply prefix
 104                 every line with one of these strings. A line that is
 105                 not prefixed will be logged at the default log level
 106                 SD_INFO.</para>
 107
 108                 <example>
 109                         <title>Hello World</title>
 110
 111                         <para>A daemon may log with the log level
 112                         NOTICE by issuing this call:</para>
 113
 114                         <programlisting>fprintf(stderr, SD_NOTICE "Hello World!\n");</programlisting>
 115                 </example>
 116         </refsect1>
 117
 118         <refsect1>
 119                 <title>Notes</title>
 120
 121                 <para>These interfaces are provided by the reference
 122                 implementation of APIs for new-style daemons and
 123                 distributed with the systemd package. The algorithms
 124                 they implement are simple, and can easily be
 125                 reimplemented in daemons if it is important to support
 126                 this interface without using the reference
 127                 implementation. See the respective function man pages
 128                 for details.</para>
 129
 130                 <para>In addition, for details about the algorithms
 131                 check the liberally licensed reference implementation
 132                 sources:
 133                 <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/sd-daemon.c"/>
 134                 resp. <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
 135
 136                 <para>These APIs are implemented in the reference
 137                 implementation's <filename>sd-daemon.c</filename> and
 138                 <filename>sd-daemon.h</filename> files. These
 139                 interfaces are available as shared library, which can
 140                 be compiled and linked to with the
 141                 <literal>libsystemd-daemon</literal>
 142                 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 143                 file. Alternatively, applications consuming these APIs
 144                 may copy the implementation into their source tree,
 145                 either verbatim or in excerpts.</para>
 146
 147                 <para>The functions directly related to new-style
 148                 daemons become NOPs when -DDISABLE_SYSTEMD is set
 149                 during compilation and the reference implementation is
 150                 used as drop-in files. In addition, if
 151                 <filename>sd-daemon.c</filename> is compiled on
 152                 non-Linux systems they become NOPs.</para>
 153         </refsect1>
 154
 155         <refsect1>
 156                 <title>See Also</title>
 157                 <para>
 158                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 159                         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 160                         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 161                         <citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 162                         <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 163                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 164                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 165                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 166                         <citerefentry><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 167                         <citerefentry><refentrytitle>sd-readahead</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 168                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 169                 </para>
 170         </refsect1>
 171
 172 </refentry>