X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=blobdiff_plain;f=man%2Fmachine-id.xml;h=73f0926c0b8862b70895abea88dab4bbbb0effdd;hb=3ab1e259d918228c68c1829bd67625e1dc660862;hp=98c09436ba41a7387519558c8d80266698b9e431;hpb=7640a5de1b3ffe6547200ad204d14e4f067caf4f;p=elogind.git
diff --git a/man/machine-id.xml b/man/machine-id.xml
index 98c09436b..73f0926c0 100644
--- a/man/machine-id.xml
+++ b/man/machine-id.xml
@@ -9,16 +9,16 @@
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 .
-->
@@ -55,21 +55,23 @@
Description
The /etc/machine-id 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.
+ 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.)
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.
+ boot if it is found to be empty.
The machine ID does not change based on user
configuration, or when hardware is replaced.
- This machine id follows the same format and
+ This machine ID adheres to the same format and
logic as the D-Bus machine ID.
Programs may use this ID to identify the host
@@ -79,6 +81,40 @@
a more useful replacement for the
gethostid3
call POSIX specifies.
+
+ The
+ systemd-machine-id-setup1
+ tool may be used by installer tools to initialize the
+ machine ID at install time.
+
+
+
+ Relation to OSF UUIDs
+
+ Note that the machine ID historically is not an
+ OSF UUID as defined by RFC
+ 4122, nor a Microsoft GUID. Starting with
+ systemd v30 newly generated machine IDs however do
+ qualify as v4 UUIDs.
+
+ 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
+ id being an unsigned character
+ array:
+
+ /* 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;
+
+ (This code is inspired by
+ generate_random_uuid() of
+ drivers/char/random.c from the
+ kernel sources.)
+
@@ -88,7 +124,7 @@
/etc/machine-id originates in the
/var/lib/dbus/machine-id file
introduced by D-Bus. In fact this latter file might be a
- symlink to the
+ symlink to
/etc/machine-id.
@@ -96,6 +132,7 @@
See Also
systemd1,
+ systemd-machine-id-setup1,
gethostid3,
hostname5,
machine-info5,