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Diffstat (limited to 'src/manpages/machine-id.xml')
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diff --git a/src/manpages/machine-id.xml b/src/manpages/machine-id.xml new file mode 100644 index 0000000000..d318ec54ec --- /dev/null +++ b/src/manpages/machine-id.xml @@ -0,0 +1,146 @@ +<?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 early 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> + + <para>The machine-id may also be set, for example when network + booting, by setting the <varname>systemd.machine_id=</varname> + kernel command line parameter or passing the option + <option>--machine-id=</option> to systemd. A machine-id may not + be set to all zeros.</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 + <filename>/etc/machine-id</filename>.</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> |