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

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   9   Copyright 2014 Didier Roche
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  24 <refentry id="systemd-machine-id-commit.service">
  25
  26   <refentryinfo>
  27     <title>systemd-machine-id-commit.service</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>Developer</contrib>
  33         <firstname>Didier</firstname>
  34         <surname>Roche</surname>
  35         <email>didrocks@ubuntu.com</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>systemd-machine-id-commit.service</refentrytitle>
  42     <manvolnum>8</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>systemd-machine-id-commit.service</refname>
  47     <refpurpose>Commit a transient machine ID to disk</refpurpose>
  48   </refnamediv>
  49
  50   <refsynopsisdiv>
  51     <para><filename>systemd-machine-id-commit.service</filename></para>
  52   </refsynopsisdiv>
  53
  54   <refsect1>
  55     <title>Description</title>
  56
  57     <para><filename>systemd-machine-id-commit.service</filename> is an
  58     early boot service responsible for committing transient
  59     <filename>/etc/machine-id</filename> files to a writable disk file
  60     system. See
  61     <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  62     for more information about machine IDs.</para>
  63
  64     <para>This service is started after
  65     <filename>local-fs.target</filename> in case
  66     <filename>/etc/machine-id</filename> is a mount point of its own
  67     (usually from a memory file system such as
  68     <literal>tmpfs</literal>) and /etc is writable. The service will
  69     invoke <command>systemd-machine-id-setup --commit</command>, which
  70     writes the current transient machine ID to disk and unmount the
  71     <filename>/etc/machine-id</filename> file in a race-free manner to
  72     ensure that file is always valid and accessible for other
  73     processes. See
  74     <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  75     for details.</para>
  76
  77     <para>The main use case of this service are systems where
  78     <filename>/etc/machine-id</filename> is read-only and initially
  79     not initialized. In this case, the system manager will generate a
  80     transient machine ID file on a memory file system, and mount it
  81     over <filename>/etc/machine-id</filename>, during the early boot
  82     phase. This service is then invoked in a later boot phase, as soon
  83     as <filename>/etc</filename> has been remounted writable and the
  84     ID may thus be committed to disk to make it permanent.</para>
  85   </refsect1>
  86
  87   <refsect1>
  88     <title>See Also</title>
  89     <para>
  90       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  91       <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  92       <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  93       <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  94     </para>
  95   </refsect1>
  96
  97 </refentry>