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diff --git a/man/machine-id.xml b/man/machine-id.xml
index 98c09436b..4b4759e48 100644
--- a/man/machine-id.xml
+++ b/man/machine-id.xml
@@ -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 .
-->
- /etc/machine-id
+ machine-id
systemd
@@ -44,7 +44,7 @@
machine-id
- local machine ID configuration file
+ Local machine ID configuration file
@@ -55,30 +55,66 @@
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, 32-character,
+ lowercase 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.
+ stateless systems, it is generated during runtime at
+ boot if it is found to be empty.
The machine ID does not change based on user
- configuration, or when hardware is replaced.
+ 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
- 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
gethostid3
- call POSIX specifies.
+ call that 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; however, starting with
+ systemd v30, newly generated machine IDs 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
+ Linux kernel sources.)
+
@@ -87,8 +123,8 @@
The simple configuration file format of
/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
+ introduced by D-Bus. In fact, this latter file might be a
+ symlink to
/etc/machine-id.
@@ -96,10 +132,13 @@
See Also
systemd1,
+ systemd-machine-id-setup1,
gethostid3,
hostname5,
machine-info5,
- os-release5
+ os-release5,
+ sd-id1283,
+ sd_id128_get_machine3