man/machine-id.xml

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   3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   4         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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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.</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>