man/sd-daemon.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   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>3</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>sd-daemon</refname>
  47                 <refname>SD_EMERG</refname>
  48                 <refname>SD_ALERT</refname>
  49                 <refname>SD_CRIT</refname>
  50                 <refname>SD_ERR</refname>
  51                 <refname>SD_WARNING</refname>
  52                 <refname>SD_NOTICE</refname>
  53                 <refname>SD_INFO</refname>
  54                 <refname>SD_DEBUG</refname>
  55                 <refpurpose>Reference implementation of APIs for
  56                 new-style daemons</refpurpose>
  57         </refnamediv>
  58
  59         <refsynopsisdiv>
  60                 <funcsynopsis>
  61                         <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
  62                 </funcsynopsis>
  63
  64                 <cmdsynopsis>
  65                         <command>pkg-config --cflags --libs libsystemd-daemon</command>
  66                 </cmdsynopsis>
  67
  68         </refsynopsisdiv>
  69
  70         <refsect1>
  71                 <title>Description</title>
  72
  73                 <para><filename>sd-daemon.c</filename> and
  74                 <filename>sd-daemon.h</filename> provide a reference
  75                 implementation of various APIs for new-style daemons,
  76                 as implemented by the
  77                 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  78                 init system.</para>
  79
  80                 <para>See
  81                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  82                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  83                 <citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  84                 <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  85                 for more information about the functions
  86                 implemented. In addition to these functions a couple
  87                 of logging prefixes are defined as macros:</para>
  88
  89                 <programlisting>#define SD_EMERG   "&lt;0&gt;"  /* system is unusable */
  90 #define SD_ALERT   "&lt;1&gt;"  /* action must be taken immediately */
  91 #define SD_CRIT    "&lt;2&gt;"  /* critical conditions */
  92 #define SD_ERR     "&lt;3&gt;"  /* error conditions */
  93 #define SD_WARNING "&lt;4&gt;"  /* warning conditions */
  94 #define SD_NOTICE  "&lt;5&gt;"  /* normal but significant condition */
  95 #define SD_INFO    "&lt;6&gt;"  /* informational */
  96 #define SD_DEBUG   "&lt;7&gt;"  /* debug-level messages */</programlisting>
  97
  98                 <para>These prefixes are intended to be used in
  99                 conjunction with STDERR-based logging as implemented
 100                 by systemd. If a systemd service definition file is
 101                 configured with <varname>StandardError=syslog</varname>
 102                 or <varname>StandardError=kmsg</varname> these
 103                 prefixes can be used to encode a log level in lines
 104                 printed. This is similar to the kernel
 105                 <function>printk()</function>-style logging. See
 106                 <citerefentry><refentrytitle>klogctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 107                 for more information.</para>
 108
 109                 <para>The log levels are identical to
 110                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s
 111                 log level system. To use these prefixes simply prefix
 112                 every line with one of these strings. A line that is
 113                 not prefixed will be logged at the default log level
 114                 SD_INFO.</para>
 115
 116                 <example>
 117                         <title>Hello World</title>
 118
 119                         <para>A daemon may log with the log level
 120                         NOTICE by issuing this call:</para>
 121
 122                         <programlisting>fprintf(stderr, SD_NOTICE "Hello World!\n");</programlisting>
 123                 </example>
 124         </refsect1>
 125
 126         <refsect1>
 127                 <title>Notes</title>
 128
 129                 <para>These interfaces are provided by the reference
 130                 implementation of APIs for new-style daemons and
 131                 distributed with the systemd package. The algorithms
 132                 they implement are simple, and can easily be
 133                 reimplemented in daemons if it is important to support
 134                 this interface without using the reference
 135                 implementation. See the respective function man pages
 136                 for details.</para>
 137
 138                 <para>In addition, for details about the algorithms
 139                 check the liberally licensed reference implementation
 140                 sources:
 141                 <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c"/>
 142                 and <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
 143
 144                 <para>These APIs are implemented in the reference
 145                 implementation's <filename>sd-daemon.c</filename> and
 146                 <filename>sd-daemon.h</filename> files. These
 147                 interfaces are available as shared library, which can
 148                 be compiled and linked to with the
 149                 <literal>libsystemd-daemon</literal>
 150                 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 151                 file. Alternatively, applications consuming these APIs
 152                 may copy the implementation into their source tree,
 153                 either verbatim or in excerpts.</para>
 154
 155                 <para>The functions directly related to new-style
 156                 daemons become NOPs when -DDISABLE_SYSTEMD is set
 157                 during compilation and the reference implementation is
 158                 used as drop-in files. In addition, if
 159                 <filename>sd-daemon.c</filename> is compiled on
 160                 non-Linux systems they become NOPs.</para>
 161         </refsect1>
 162
 163         <refsect1>
 164                 <title>See Also</title>
 165                 <para>
 166                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 167                         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 168                         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 169                         <citerefentry><refentrytitle>sd_booted</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 170                         <citerefentry><refentrytitle>sd_is_fifo</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 171                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 172                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 173                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 174                         <citerefentry><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 175                         <citerefentry><refentrytitle>sd-readahead</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 176                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 177                 </para>
 178         </refsect1>
 179
 180 </refentry>