<?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>