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

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   3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!--
   5   SPDX-License-Identifier: LGPL-2.1+
   6
   7   This file is part of systemd.
   8
   9   Copyright 2014 Didier Roche
  10 -->
  11 <refentry id="systemd-machine-id-commit.service">
  12
  13   <refentryinfo>
  14     <title>systemd-machine-id-commit.service</title>
  15     <productname>systemd</productname>
  16
  17     <authorgroup>
  18       <author>
  19         <contrib>Developer</contrib>
  20         <firstname>Didier</firstname>
  21         <surname>Roche</surname>
  22         <email>didrocks@ubuntu.com</email>
  23       </author>
  24     </authorgroup>
  25   </refentryinfo>
  26
  27   <refmeta>
  28     <refentrytitle>systemd-machine-id-commit.service</refentrytitle>
  29     <manvolnum>8</manvolnum>
  30   </refmeta>
  31
  32   <refnamediv>
  33     <refname>systemd-machine-id-commit.service</refname>
  34     <refpurpose>Commit a transient machine ID to disk</refpurpose>
  35   </refnamediv>
  36
  37   <refsynopsisdiv>
  38     <para><filename>systemd-machine-id-commit.service</filename></para>
  39   </refsynopsisdiv>
  40
  41   <refsect1>
  42     <title>Description</title>
  43
  44     <para><filename>systemd-machine-id-commit.service</filename> is an
  45     early boot service responsible for committing transient
  46     <filename>/etc/machine-id</filename> files to a writable disk file
  47     system. See
  48     <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  49     for more information about machine IDs.</para>
  50
  51     <para>This service is started after
  52     <filename>local-fs.target</filename> in case
  53     <filename>/etc/machine-id</filename> is a mount point of its own
  54     (usually from a memory file system such as
  55     <literal>tmpfs</literal>) and /etc is writable. The service will
  56     invoke <command>systemd-machine-id-setup --commit</command>, which
  57     writes the current transient machine ID to disk and unmount the
  58     <filename>/etc/machine-id</filename> file in a race-free manner to
  59     ensure that file is always valid and accessible for other
  60     processes. See
  61     <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  62     for details.</para>
  63
  64     <para>The main use case of this service are systems where
  65     <filename>/etc/machine-id</filename> is read-only and initially
  66     not initialized. In this case, the system manager will generate a
  67     transient machine ID file on a memory file system, and mount it
  68     over <filename>/etc/machine-id</filename>, during the early boot
  69     phase. This service is then invoked in a later boot phase, as soon
  70     as <filename>/etc</filename> has been remounted writable and the
  71     ID may thus be committed to disk to make it permanent.</para>
  72   </refsect1>
  73
  74   <refsect1>
  75     <title>See Also</title>
  76     <para>
  77       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  78       <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  79       <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  80       <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  81     </para>
  82   </refsect1>
  83
  84 </refentry>