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 transient machine-id to disk</refpurpose>
  46   </refnamediv>
  47
  48   <refsynopsisdiv>
  49     <para><filename>systemd-machine-id-commit.service</filename></para>
  50     <para><filename>/usr/lib/systemd/systemd-machine-id-commit</filename></para>
  51   </refsynopsisdiv>
  52
  53   <refsect1>
  54     <title>Description</title>
  55
  56     <para><filename>systemd-machine-id-commit.service</filename> is a
  57     service responsible for committing any transient
  58     <filename>/etc/machine-id</filename> file to a writable file
  59     system. See
  60     <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  61     for more information about this file.</para>
  62
  63     <para>This service is started shortly after
  64     <filename>local-fs.target</filename> if
  65     <filename>/etc/machine-id</filename> is an independent mount point
  66     (probably a tmpfs one) and /etc is writable.
  67     <command>systemd-machine-id-commit</command> will then write
  68     current machine ID to disk and unmount the transient
  69     <filename>/etc/machine-id</filename> file in a race-free manner to
  70     ensure that file is always valid for other processes.</para>
  71
  72     <para>Note that the traditional way to initialize the machine ID
  73     in <filename>/etc/machine-id</filename> is to use
  74     <command>systemd-machine-id-setup</command> by system installer
  75     tools. You can also use
  76     <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  77     to initialize the machine ID on mounted (but not booted) system
  78     images. The main use case for that service is
  79     <filename>/etc/machine-id</filename> being an empty file at boot
  80     and initrd chaining to systemd giving it a read only file system
  81     that will be turned read-write later during the boot
  82     process.</para>
  83
  84     <para>There is no consequence if that service fails other than a
  85     newer machine-id will be generated during next system boot.
  86     </para>
  87   </refsect1>
  88
  89   <refsect1>
  90     <title>See Also</title>
  91     <para>
  92       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  93       <citerefentry><refentrytitle>systemd-machine-id-commit</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  94       <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  95       <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  96       <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  97     </para>
  98   </refsect1>
  99
 100 </refentry>