systemd-machine-id-commit.service.xml revision 681eb9cf2b831293a4f3d4c48a748d2e4a25d69e
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This file is part of systemd.
Copyright 2014 Didier Roche
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<refentry id="systemd-machine-id-commit.service">
<refentryinfo>
<title>systemd-machine-id-commit.service</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Didier</firstname>
<surname>Roche</surname>
<email>didrocks@ubuntu.com</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-machine-id-commit.service</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-machine-id-commit.service</refname>
<refpurpose>Commit transient machine-id to disk</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>systemd-machine-id-commit.service</filename></para>
<para><filename>&rootlibexecdir;/systemd-machine-id-commit</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>systemd-machine-id-commit.service</filename> is a
service responsible for committing any transient
<filename>/etc/machine-id</filename> file to a writable file
system. See
<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for more information about this file.</para>
<para>This service is started shortly after
<filename>local-fs.target</filename> if
<filename>/etc/machine-id</filename> is an independent mount point
(probably a tmpfs one) and /etc is writable.
<command>systemd-machine-id-commit</command> will then write
current machine ID to disk and unmount the transient
<filename>/etc/machine-id</filename> file in a race-free manner to
ensure that file is always valid for other processes.</para>
<para>Note that the traditional way to initialize the machine ID
in <filename>/etc/machine-id</filename> is to use
<command>systemd-machine-id-setup</command> by system installer
tools. You can also use
<citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
to initialize the machine ID on mounted (but not booted) system
images. The main use case for that service is
<filename>/etc/machine-id</filename> being an empty file at boot
and initrd chaining to systemd giving it a read only file system
that will be turned read-write later during the boot
process.</para>
<para>There is no consequence if that service fails other than a
newer machine-id will be generated during next system boot.
</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-machine-id-commit</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>