dbus-uuidgen [--version] [--ensure[=FILENAME]] [--get[=FILENAME]]
The dbus-uuidgen command generates or reads a universally unique ID.
Note that the D-Bus UUID has no relationship to RFC 4122 and does not generate UUIDs compatible with that spec. Many systems have a separate command for that (often called "uuidgen").
See http://www.freedesktop.org/software/dbus/ for more information about D-Bus.
The primary usage of dbus-uuidgen is to run in the post-install script of a D-Bus package like this:
This will ensure that /var/lib/dbus/machine-id exists and has the uuid in it. It won't overwrite an existing uuid, since this id should remain fixed for a single machine until the next reboot at least.
The important properties of the machine UUID are that 1) it remains unchanged until the next reboot and 2) it is different for any two running instances of the OS kernel. That is, if two processes see the same UUID, they should also see the same shared memory, UNIX domain sockets, local X displays, localhost.localdomain resolution, process IDs, and so forth.
If you run dbus-uuidgen with no options it just prints a new uuid made up out of thin air.
If you run it with --get, it prints the machine UUID by default, or the UUID in the specified file if you specify a file.
If you try to change an existing machine-id on a running system, it will probably result in bad things happening. Don't try to change this file. Also, don't make it the same on two different systems; it needs to be different anytime there are two different kernels running.
The UUID should be different on two different virtual machines, because there are two different kernels.