man/systemd-machine-id-commit.service.xml

   1 <?xml version="1.0"?>
   2 <!--*-nxml-*-->
   3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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   5   This file is part of systemd.
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   7   Copyright 2014 Didier Roche
   8
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  22 <refentry id="systemd-machine-id-commit.service">
  23
  24         <refentryinfo>
  25                 <title>systemd-machine-id-commit.service</title>
  26                 <productname>systemd</productname>
  27
  28                 <authorgroup>
  29                         <author>
  30                                 <contrib>Developer</contrib>
  31                                 <firstname>Didier</firstname>
  32                                 <surname>Roche</surname>
  33                                 <email>didrocks@ubuntu.com</email>
  34                         </author>
  35                 </authorgroup>
  36         </refentryinfo>
  37
  38         <refmeta>
  39                 <refentrytitle>systemd-machine-id-commit.service</refentrytitle>
  40                 <manvolnum>8</manvolnum>
  41         </refmeta>
  42
  43         <refnamediv>
  44                 <refname>systemd-machine-id-commit.service</refname>
  45                 <refpurpose>Commit transient machine-id to disk</refpurpose>
  46         </refnamediv>
  47
  48         <refsynopsisdiv>
  49                 <para><filename>systemd-machine-id-commit.service</filename></para>
  50                 <para><filename>/usr/lib/systemd/systemd-machine-id-commit</filename></para>
  51         </refsynopsisdiv>
  52
  53         <refsect1>
  54                 <title>Description</title>
  55
  56                 <para><filename>systemd-machine-id-commit.service</filename> is
  57                 a service responsible for committing any transient
  58                 <filename>/etc/machine-id</filename> file to a writable file
  59                 system. See
  60                 <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  61                 for more information about this file.</para>
  62
  63                 <para>This service is started shortly after
  64                 <filename>local-fs.target</filename> if
  65                 <filename>/etc/machine-id</filename> is an independent mount
  66                 point (probably a tmpfs one) and /etc is writable.
  67                 <command>systemd-machine-id-commit</command> will then
  68                 write current machine ID to disk and unmount the transient
  69                 <filename>/etc/machine-id</filename> file in a race-free
  70                 manner to ensure that file is always valid for other
  71                 processes.</para>
  72
  73                 <para>Note that the traditional way to initialize the machine
  74                 ID in <filename>/etc/machine-id</filename> is to use
  75                 <command>systemd-machine-id-setup</command> by system
  76                 installer tools. You can also use
  77                 <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  78                 to initialize the machine ID on mounted (but not
  79                 booted) system images. The main use case for that service is
  80                 <filename>/etc/machine-id</filename> being an empty file at
  81                 boot and initrd chaining to systemd giving it a read only file
  82                 system that will be turned read-write later during the boot
  83                 process.</para>
  84
  85                 <para>There is no consequence if that service fails other than
  86                 a newer machine-id will be generated during next system boot.
  87                 </para>
  88         </refsect1>
  89
  90         <refsect1>
  91                 <title>See Also</title>
  92                 <para>
  93                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  94                         <citerefentry><refentrytitle>systemd-machine-id-commit</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  95                         <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  96                         <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  97                         <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  98                 </para>
  99         </refsect1>
 100
 101 </refentry>