man/sd_id128_get_machine.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 2012 Lennart Poettering
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  23
  24 <refentry id="sd_id128_get_machine">
  25
  26         <refentryinfo>
  27                 <title>sd_id128_get_machine</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_id128_get_machine</refentrytitle>
  42                 <manvolnum>3</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>sd_id128_get_machine</refname>
  47                 <refname>sd_id128_get_boot</refname>
  48                 <refpurpose>Retrieve 128 bit IDs</refpurpose>
  49         </refnamediv>
  50
  51         <refsynopsisdiv>
  52                 <funcsynopsis>
  53                         <funcsynopsisinfo>#include &lt;systemd/sd-id128.h&gt;</funcsynopsisinfo>
  54
  55                         <funcprototype>
  56                                 <funcdef>int <function>sd_id128_get_machine</function></funcdef>
  57                                 <paramdef>sd_id128_t* <parameter>ret</parameter></paramdef>
  58                         </funcprototype>
  59
  60                         <funcprototype>
  61                                 <funcdef>int <function>sd_id128_get_boot</function></funcdef>
  62                                 <paramdef>sd_id128_t* <parameter>ret</parameter></paramdef>
  63                         </funcprototype>
  64
  65                 </funcsynopsis>
  66         </refsynopsisdiv>
  67
  68         <refsect1>
  69                 <title>Description</title>
  70
  71                 <para><function>sd_id128_get_machine()</function>
  72                 returns the machine ID of the executing host. This
  73                 reads and parses the
  74                 <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  75                 file. This function caches the machine ID internally
  76                 to make retrieving the machine ID a cheap
  77                 operation.</para>
  78
  79                 <para><function>sd_id128_get_boot()</function> returns
  80                 the boot ID of the executing kernel. This reads and
  81                 parses the
  82                 <filename>/proc/sys/kernel/random/boot_id</filename>
  83                 file exposed by the kernel. It is randomly generated
  84                 early at boot and is unique for every running kernel
  85                 instance. See
  86                 <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry>
  87                 for more information. This function also internally
  88                 caches the returned ID to make this call a cheap
  89                 operation.</para>
  90
  91                 <para>Note that
  92                 <function>sd_id128_get_boot()</function> always returns
  93                 a UUID v4 compatible
  94                 ID. <function>sd_id128_get_machine()</function> will
  95                 also return a UUID v4 compatible ID on new
  96                 installations, but might not on older. It is possible
  97                 to convert the machine ID into an UUID v4 compatible
  98                 one. For more information see
  99                 <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 100
 101                 <para>For more information about the
 102                 <literal>sd_id128_t</literal> type see
 103                 <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 104         </refsect1>
 105
 106         <refsect1>
 107                 <title>Return Value</title>
 108
 109                 <para>The two calls return 0 on success (in which
 110                 case <parameter>ret</parameter> is filled in), or a
 111                 negative errno-style error code.</para>
 112         </refsect1>
 113
 114         <refsect1>
 115                 <title>Notes</title>
 116
 117                 <para>The <function>sd_id128_get_machine()</function>
 118                 and <function>sd_id128_get_boot()</function>
 119                 interfaces are available as shared library, which can
 120                 be compiled and linked to with the
 121                 <literal>libsystemd-id128</literal>
 122                 <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 123                 file.</para>
 124         </refsect1>
 125
 126         <refsect1>
 127                 <title>See Also</title>
 128
 129                 <para>
 130                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 131                         <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 132                         <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 133                         <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry>,
 134                         <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 135                 </para>
 136         </refsect1>
 137
 138 </refentry>