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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 a transient machine ID to disk</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>systemd-machine-id-commit.service</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>systemd-machine-id-commit.service</filename> is an
early boot service responsible for committing transient
<filename>/etc/machine-id</filename> files to a writable disk file
system. See
<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for more information about machine IDs.</para>
<para>This service is started after
<filename>local-fs.target</filename> in case
<filename>/etc/machine-id</filename> is a mount point of its own
(usually from a memory file system such as
<literal>tmpfs</literal>) and /etc is writable. The service will
invoke <command>systemd-machine-id-setup --commit</command>, which
writes the current transient machine ID to disk and unmount the
<filename>/etc/machine-id</filename> file in a race-free manner to
ensure that file is always valid and accessible for other
processes. See
<citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>
for details.</para>
<para>The main use case of this service are systems where
<filename>/etc/machine-id</filename> is read-only and initially
not initialized. In this case, the system manager will generate a
transient machine ID file on a memory file system, and mount it
over <filename>/etc/machine-id</filename>, during the early boot
phase. This service is then invoked in a later boot phase, as soon
as <filename>/etc</filename> has been remounted writable and the
ID may thus be committed to disk to make it permanent.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</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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