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

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