man/machine-id.xml

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   3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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   7   This file is part of systemd.
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   9   Copyright 2010 Lennart Poettering
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  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 if it is found to be empty.</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 for 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                           <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 102                           <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 103                   </para>
 104         </refsect1>
 105
 106 </refentry>