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diff --git a/man/machine-id.xml b/man/machine-id.xml new file mode 100644 index 0000000000..7d424b705b --- /dev/null +++ b/man/machine-id.xml @@ -0,0 +1,145 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<?xml-stylesheet type="text/xsl" href="http://docbook.sourceforge.net/release/xsl/current/xhtml/docbook.xsl"?> +<!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>/etc/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, lowercase 32 + character 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, that 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><refentrytitle>gethostid</refentrytitle><manvolnum>3</manvolnum></citerefentry> + call 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.</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="http://tools.ietf.org/html/rfc4122">RFC + 4122</ulink>, nor a Microsoft GUID. Starting with + systemd v30 newly generated machine IDs however 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 + 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><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> + </para> + </refsect1> + +</refentry> |