3 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
5 SPDX-License-Identifier: LGPL-2.1+
7 This file is part of systemd.
9 Copyright 2014 Didier Roche
11 <refentry id=
"systemd-machine-id-commit.service">
14 <title>systemd-machine-id-commit.service
</title>
15 <productname>systemd
</productname>
19 <contrib>Developer
</contrib>
20 <firstname>Didier
</firstname>
21 <surname>Roche
</surname>
22 <email>didrocks@ubuntu.com
</email>
28 <refentrytitle>systemd-machine-id-commit.service
</refentrytitle>
29 <manvolnum>8</manvolnum>
33 <refname>systemd-machine-id-commit.service
</refname>
34 <refpurpose>Commit a transient machine ID to disk
</refpurpose>
38 <para><filename>systemd-machine-id-commit.service
</filename></para>
42 <title>Description
</title>
44 <para><filename>systemd-machine-id-commit.service
</filename> is an
45 early boot service responsible for committing transient
46 <filename>/etc/machine-id
</filename> files to a writable disk file
48 <citerefentry><refentrytitle>machine-id
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
49 for more information about machine IDs.
</para>
51 <para>This service is started after
52 <filename>local-fs.target
</filename> in case
53 <filename>/etc/machine-id
</filename> is a mount point of its own
54 (usually from a memory file system such as
55 <literal>tmpfs
</literal>) and /etc is writable. The service will
56 invoke
<command>systemd-machine-id-setup --commit
</command>, which
57 writes the current transient machine ID to disk and unmount the
58 <filename>/etc/machine-id
</filename> file in a race-free manner to
59 ensure that file is always valid and accessible for other
61 <citerefentry><refentrytitle>systemd-machine-id-setup
</refentrytitle><manvolnum>1</manvolnum></citerefentry>
64 <para>The main use case of this service are systems where
65 <filename>/etc/machine-id
</filename> is read-only and initially
66 not initialized. In this case, the system manager will generate a
67 transient machine ID file on a memory file system, and mount it
68 over
<filename>/etc/machine-id
</filename>, during the early boot
69 phase. This service is then invoked in a later boot phase, as soon
70 as
<filename>/etc
</filename> has been remounted writable and the
71 ID may thus be committed to disk to make it permanent.
</para>
75 <title>See Also
</title>
77 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
78 <citerefentry><refentrytitle>systemd-machine-id-setup
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
79 <citerefentry><refentrytitle>machine-id
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
80 <citerefentry><refentrytitle>systemd-firstboot
</refentrytitle><manvolnum>1</manvolnum></citerefentry>