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1 <?xml version="1.0"?>
2 <!--*-nxml-*-->
3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4 <!--
5 SPDX-License-Identifier: LGPL-2.1+
6
7 Copyright © 2014 Didier Roche
8 -->
9 <refentry id="systemd-machine-id-commit.service">
10
11 <refentryinfo>
12 <title>systemd-machine-id-commit.service</title>
13 <productname>systemd</productname>
14 </refentryinfo>
15
16 <refmeta>
17 <refentrytitle>systemd-machine-id-commit.service</refentrytitle>
18 <manvolnum>8</manvolnum>
19 </refmeta>
20
21 <refnamediv>
22 <refname>systemd-machine-id-commit.service</refname>
23 <refpurpose>Commit a transient machine ID to disk</refpurpose>
24 </refnamediv>
25
26 <refsynopsisdiv>
27 <para><filename>systemd-machine-id-commit.service</filename></para>
28 </refsynopsisdiv>
29
30 <refsect1>
31 <title>Description</title>
32
33 <para><filename>systemd-machine-id-commit.service</filename> is an
34 early boot service responsible for committing transient
35 <filename>/etc/machine-id</filename> files to a writable disk file
36 system. See
37 <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
38 for more information about machine IDs.</para>
39
40 <para>This service is started after
41 <filename>local-fs.target</filename> in case
42 <filename>/etc/machine-id</filename> is a mount point of its own
43 (usually from a memory file system such as
44 <literal>tmpfs</literal>) and /etc is writable. The service will
45 invoke <command>systemd-machine-id-setup --commit</command>, which
46 writes the current transient machine ID to disk and unmount the
47 <filename>/etc/machine-id</filename> file in a race-free manner to
48 ensure that file is always valid and accessible for other
49 processes. See
50 <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>
51 for details.</para>
52
53 <para>The main use case of this service are systems where
54 <filename>/etc/machine-id</filename> is read-only and initially
55 not initialized. In this case, the system manager will generate a
56 transient machine ID file on a memory file system, and mount it
57 over <filename>/etc/machine-id</filename>, during the early boot
58 phase. This service is then invoked in a later boot phase, as soon
59 as <filename>/etc</filename> has been remounted writable and the
60 ID may thus be committed to disk to make it permanent.</para>
61 </refsect1>
62
63 <refsect1>
64 <title>See Also</title>
65 <para>
66 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
67 <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
68 <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
69 <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
70 </para>
71 </refsect1>
72
73 </refentry>