chiark / gitweb /
man: update sd_bus_request_name() man page
[elogind.git] / man / machine-id.xml
index d0bfbd2..4b4759e 100644 (file)
@@ -9,22 +9,22 @@
   Copyright 2010 Lennart Poettering
 
   systemd is free software; you can redistribute it and/or modify it
-  under the terms of the GNU General Public License as published by
-  the Free Software Foundation; either version 2 of the License, or
+  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
-  General Public License for more details.
+  Lesser General Public License for more details.
 
-  You should have received a copy of the GNU General Public License
+  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>
+                <title>machine-id</title>
                 <productname>systemd</productname>
 
                 <authorgroup>
@@ -44,7 +44,7 @@
 
         <refnamediv>
                 <refname>machine-id</refname>
-                <refpurpose>local machine ID configuration file</refpurpose>
+                <refpurpose>Local machine ID configuration file</refpurpose>
         </refnamediv>
 
         <refsynopsisdiv>
                 <title>Description</title>
 
                 <para>The <filename>/etc/machine-id</filename> file
-                configures the unique machine id of the local system
-                that is set during installation. It should contain a
-                single newline-terminated, hexadecimal, lowercase 16
-                character machine ID string.</para>
+                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
+                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>
+                configuration or when hardware is replaced.</para>
 
-                <para>This machine id follows the same format and
+                <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
+                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
+                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>
+                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.</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] &amp; 0x0F) | 0x40;
+/* Set the UUID variant to DCE */
+id[8] = (id[8] &amp; 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>
                 <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 the
+                introduced by D-Bus. In fact, this latter file might be a
+                symlink to
                 <varname>/etc/machine-id</varname>.</para>
         </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>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>