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strv: detect non-assignments in env blocks properly in env_append()
[elogind.git] / man / machine-id.xml
1 <?xml version='1.0'?> <!--*-nxml-*-->
2 <?xml-stylesheet type="text/xsl" href="http://docbook.sourceforge.net/release/xsl/current/xhtml/docbook.xsl"?>
3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
4         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
5
6 <!--
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9   Copyright 2010 Lennart Poettering
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23 -->
24
25 <refentry id="machine-id">
26         <refentryinfo>
27                 <title>/etc/machine-id</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>machine-id</refentrytitle>
42                 <manvolnum>5</manvolnum>
43         </refmeta>
44
45         <refnamediv>
46                 <refname>machine-id</refname>
47                 <refpurpose>local machine ID configuration file</refpurpose>
48         </refnamediv>
49
50         <refsynopsisdiv>
51                 <para><filename>/etc/machine-id</filename></para>
52         </refsynopsisdiv>
53
54         <refsect1>
55                 <title>Description</title>
56
57                 <para>The <filename>/etc/machine-id</filename> file
58                 configures the unique machine id of the local system
59                 that is set during installation. It should contain a
60                 single newline-terminated, hexadecimal, lowercase 16
61                 character machine ID string.</para>
62
63                 <para>The machine ID is usually generated from a
64                 random source during system installation and stays
65                 constant for all subsequent boots. Optionally, for
66                 stateless systems it is generated during runtime at
67                 boot.</para>
68
69                 <para>The machine ID does not change based on user
70                 configuration, or when hardware is replaced.</para>
71
72                 <para>This machine id follows the same format and
73                 logic as the D-Bus machine ID.</para>
74
75                 <para>Programs may use this ID to identify the host
76                 with a globally unique ID in the network, that does
77                 not change even if the local network configuration
78                 changes. Due to this and its greater length it is
79                 a more useful replacement than the
80                 <citerefentry><refentrytitle>gethostid</refentrytitle><manvolnum>3</manvolnum></citerefentry>
81                 call POSIX specifies.</para>
82         </refsect1>
83
84         <refsect1>
85                 <title>History</title>
86
87                 <para>The simple configuration file format of
88                 <filename>/etc/machine-id</filename> originates in the
89                 <filename>/var/lib/dbus/machine-id</filename> file
90                 introduced by D-Bus. In fact this latter file might be a
91                 symlink to the
92                 <varname>/etc/machine-id</varname>.</para>
93         </refsect1>
94
95         <refsect1>
96                   <title>See Also</title>
97                   <para>
98                           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
99                           <citerefentry><refentrytitle>gethostid</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
100                           <citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>5</manvolnum></citerefentry>
101                   </para>
102         </refsect1>
103
104 </refentry>