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

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  22 <refentry id="systemd-machine-id-commit.service">
  23
  24   <refentryinfo>
  25     <title>systemd-machine-id-commit.service</title>
  26     <productname>systemd</productname>
  27
  28     <authorgroup>
  29       <author>
  30         <contrib>Developer</contrib>
  31         <firstname>Didier</firstname>
  32         <surname>Roche</surname>
  33         <email>didrocks@ubuntu.com</email>
  34       </author>
  35     </authorgroup>
  36   </refentryinfo>
  37
  38   <refmeta>
  39     <refentrytitle>systemd-machine-id-commit.service</refentrytitle>
  40     <manvolnum>8</manvolnum>
  41   </refmeta>
  42
  43   <refnamediv>
  44     <refname>systemd-machine-id-commit.service</refname>
  45     <refpurpose>Commit a transient machine ID to disk</refpurpose>
  46   </refnamediv>
  47
  48   <refsynopsisdiv>
  49     <para><filename>systemd-machine-id-commit.service</filename></para>
  50   </refsynopsisdiv>
  51
  52   <refsect1>
  53     <title>Description</title>
  54
  55     <para><filename>systemd-machine-id-commit.service</filename> is an
  56     early boot service responsible for committing transient
  57     <filename>/etc/machine-id</filename> files to a writable disk file
  58     system. See
  59     <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  60     for more information about machine IDs.</para>
  61
  62     <para>This service is started after
  63     <filename>local-fs.target</filename> in case
  64     <filename>/etc/machine-id</filename> is a mount point of its own
  65     (usually from a memory file system such as
  66     <literal>tmpfs</literal>) and /etc is writable. The service will
  67     invoke <command>systemd-machine-id-setup --commit</command>, which
  68     writes the current transient machine ID to disk and unmount the
  69     <filename>/etc/machine-id</filename> file in a race-free manner to
  70     ensure that file is always valid and accessible for other
  71     processes. See
  72     <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  73     for details.</para>
  74
  75     <para>The main use case of this service are systems where
  76     <filename>/etc/machine-id</filename> is read-only and initially
  77     not initialized. In this case, the system manager will generate a
  78     transient machine ID file on a memory file system, and mount it
  79     over <filename>/etc/machine-id</filename>, during the early boot
  80     phase. This service is then invoked in a later boot phase, as soon
  81     as <filename>/etc</filename> has been remounted writable and the
  82     ID may thus be committed to disk to make it permanent.</para>
  83   </refsect1>
  84
  85   <refsect1>
  86     <title>See Also</title>
  87     <para>
  88       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  89       <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  90       <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  91       <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  92     </para>
  93   </refsect1>
  94
  95 </refentry>