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

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