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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">
4
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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 a 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 a shared library, which can
120                 be compiled and linked to with the
121                 <literal>libsystemd</literal> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
122                 file.</para>
123         </refsect1>
124
125         <refsect1>
126                 <title>See Also</title>
127
128                 <para>
129                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
130                         <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
131                         <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
132                         <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry>,
133                         <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>
134                 </para>
135         </refsect1>
136
137 </refentry>