man/sd-daemon.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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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>7</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 "sd-daemon.h"</funcsynopsisinfo>
  54                 </funcsynopsis>
  55         </refsynopsisdiv>
  56
  57         <refsect1>
  58                 <title>Description</title>
  59
  60                 <para><filename>sd-daemon.c</filename> and
  61                 <filename>sd-daemon.h</filename> provide a reference
  62                 implementation of various APIs for new-style daemons,
  63                 as implemented by the
  64                 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  65                 init system.</para>
  66
  67                 <para>See
  68                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  69                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  70                 <citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  71                 <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  72                 for more information about the functions
  73                 implemented. In addition to these functions a couple
  74                 of logging prefixes are defined as macros:</para>
  75
  76                 <programlisting>#define SD_EMERG   "&lt;0&gt;"  /* system is unusable */
  77 #define SD_ALERT   "&lt;1&gt;"  /* action must be taken immediately */
  78 #define SD_CRIT    "&lt;2&gt;"  /* critical conditions */
  79 #define SD_ERR     "&lt;3&gt;"  /* error conditions */
  80 #define SD_WARNING "&lt;4&gt;"  /* warning conditions */
  81 #define SD_NOTICE  "&lt;5&gt;"  /* normal but significant condition */
  82 #define SD_INFO    "&lt;6&gt;"  /* informational */
  83 #define SD_DEBUG   "&lt;7&gt;"  /* debug-level messages */</programlisting>
  84
  85                 <para>These prefixes are intended to be used in
  86                 conjunction with STDERR-based logging as implemented
  87                 by systemd. If a systemd service definition file is
  88                 configured with <varname>StandardError=syslog</varname>
  89                 or <varname>StandardError=kmsg</varname> these
  90                 prefixes can be used to encode a log level in lines
  91                 printed. This is similar to the kernel
  92                 <function>printk()</function>-style logging. See
  93                 <citerefentry><refentrytitle>klogctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
  94                 for more information.</para>
  95
  96                 <para>The log levels are identical to
  97                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s
  98                 log level system. To use these prefixes simply prefix
  99                 every line with one of these strings. A line that is
 100                 not prefixed will be logged at the default log level
 101                 SD_INFO.</para>
 102
 103                 <example>
 104                         <title>Hello World</title>
 105
 106                         <para>A daemon may log with the log level
 107                         NOTICE by issuing this call:</para>
 108
 109                         <programlisting>fprintf(stderr, SD_NOTICE "Hello World!\n");</programlisting>
 110                 </example>
 111         </refsect1>
 112
 113         <refsect1>
 114                 <title>Notes</title>
 115
 116                 <para>These interfaces are provided by the reference
 117                 implementation of APIs for new-style daemons and
 118                 distributed with the systemd package. The algorithms
 119                 they implement are simple, and can easily be
 120                 reimplemented in daemons if it is important to support
 121                 this interface without using the reference
 122                 implementation. See the respective function man pages
 123                 for details.</para>
 124
 125                 <para>In addition, for details about the algorithms
 126                 check the liberally licensed reference implementation
 127                 sources:
 128                 <ulink url="http://cgit.freedesktop.org/systemd/tree/src/sd-daemon.c"/>
 129                 resp. <ulink url="http://cgit.freedesktop.org/systemd/tree/src/sd-daemon.h"/></para>
 130
 131                 <para>These APIs are implemented in the reference
 132                 implementation's drop-in
 133                 <filename>sd-daemon.c</filename> and
 134                 <filename>sd-daemon.h</filename> files. It is
 135                 recommended that applications consuming these APIs copy
 136                 the implementation into their source tree, either
 137                 verbatim or in excerpts. These interfaces are
 138                 currently not available in a dynamic library.</para>
 139
 140                 <para>The functions directly related to new-style
 141                 daemons become NOPs when -DDISABLE_SYSTEMD is set
 142                 during compilation. In addition, if
 143                 <filename>sd-daemon.c</filename> is compiled on
 144                 non-Linux systems they become NOPs, too.</para>
 145         </refsect1>
 146
 147         <refsect1>
 148                 <title>See Also</title>
 149                 <para>
 150                         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 151                         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 152                         <citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 153                         <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 154                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 155                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 156                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 157                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 158                         <citerefentry><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 159                 </para>
 160         </refsect1>
 161
 162 </refentry>