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<?xml version="1.0"?>
<!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2014 Didier Roche
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<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>/usr/lib/systemd/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>
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