<?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>