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