+++ /dev/null
-<?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 2010 Lennart Poettering
-
- 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="machine-id">
- <refentryinfo>
- <title>machine-id</title>
- <productname>systemd</productname>
-
- <authorgroup>
- <author>
- <contrib>Developer</contrib>
- <firstname>Lennart</firstname>
- <surname>Poettering</surname>
- <email>lennart@poettering.net</email>
- </author>
- </authorgroup>
- </refentryinfo>
-
- <refmeta>
- <refentrytitle>machine-id</refentrytitle>
- <manvolnum>5</manvolnum>
- </refmeta>
-
- <refnamediv>
- <refname>machine-id</refname>
- <refpurpose>Local machine ID configuration file</refpurpose>
- </refnamediv>
-
- <refsynopsisdiv>
- <para><filename>/etc/machine-id</filename></para>
- </refsynopsisdiv>
-
- <refsect1>
- <title>Description</title>
-
- <para>The <filename>/etc/machine-id</filename> file contains the
- unique machine ID of the local system that is set during
- installation. The machine ID is a single newline-terminated,
- hexadecimal, 32-character, lowercase machine ID string. When
- decoded from hexadecimal, this corresponds with a 16-byte/128-bit
- string.</para>
-
- <para>The machine ID is usually generated from a random source
- during system installation and stays constant for all subsequent
- boots. Optionally, for stateless systems, it is generated during
- runtime at boot if it is found to be empty.</para>
-
- <para>The machine ID does not change based on user configuration
- or when hardware is replaced.</para>
-
- <para>This machine ID adheres to the same format and logic as the
- D-Bus machine ID.</para>
-
- <para>Programs may use this ID to identify the host with a
- globally unique ID in the network, which does not change even if
- the local network configuration changes. Due to this and its
- greater length, it is a more useful replacement for the
- <citerefentry project='man-pages'><refentrytitle>gethostid</refentrytitle><manvolnum>3</manvolnum></citerefentry>
- call that POSIX specifies.</para>
-
- <para>The
- <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- tool may be used by installer tools to initialize the machine ID
- at install time. Use
- <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- to initialize it on mounted (but not booted) system images.</para>
- </refsect1>
-
- <refsect1>
- <title>Relation to OSF UUIDs</title>
-
- <para>Note that the machine ID historically is not an OSF UUID as
- defined by <ulink url="https://tools.ietf.org/html/rfc4122">RFC
- 4122</ulink>, nor a Microsoft GUID; however, starting with systemd
- v30, newly generated machine IDs do qualify as v4 UUIDs.</para>
-
- <para>In order to maintain compatibility with existing
- installations, an application requiring a UUID should decode the
- machine ID, and then apply the following operations to turn it
- into a valid OSF v4 UUID. With <literal>id</literal> being an
- unsigned character array:</para>
-
- <programlisting>/* Set UUID version to 4 --- truly random generation */
-id[6] = (id[6] & 0x0F) | 0x40;
-/* Set the UUID variant to DCE */
-id[8] = (id[8] & 0x3F) | 0x80;</programlisting>
-
- <para>(This code is inspired by
- <literal>generate_random_uuid()</literal> of
- <filename>drivers/char/random.c</filename> from the Linux kernel
- sources.)</para>
-
- </refsect1>
-
- <refsect1>
- <title>History</title>
-
- <para>The simple configuration file format of
- <filename>/etc/machine-id</filename> originates in the
- <filename>/var/lib/dbus/machine-id</filename> file introduced by
- D-Bus. In fact, this latter file might be a symlink to
- <varname>/etc/machine-id</varname>.</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 project='man-pages'><refentrytitle>gethostid</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- </para>
- </refsect1>
-
-</refentry>
~ianmdlvl / elogind.git / blobdiff