Re: Generating new IDs for cloning
On Thu, 8 Aug 2019 22:59:05 +0100, Simon McVittie <smcv@debian.org>
wrote:
>On Thu, 08 Aug 2019 at 08:37:16 -0400, Marvin Renich wrote:
>> Does anyone know what applications use this file for what purpose? Is
>> this a systemd-ism?
>
>It originated as /var/lib/dbus/machine-id in D-Bus, and systemd picked it
>up and generalized it into something non-D-Bus-specific. It isn't really
>particularly specific to either D-Bus or systemd: they both provide it
>as a piece of generically useful functionality for anything else that
>wants it. Asking which applications use it is a bit like asking which
>applications use gethostname(2): you are not going to get an exhaustive
>list unless you use something like codesearch.
>
>It's intended as an opaque, non-human-meaningful, persistent unique
>identifier for a machine (or more precisely an OS installation), used as
>a lookup key in state/configuration storage in the same sorts of places
>you might be tempted to use a hostname.
>
>Being opaque and non-human-meaningful is important for some of the
>places where it's useful, because if a string is human-meaningful (like a
>hostname), then people will sometimes want to change it, and when they do,
>anything that was recording machine-specific state with the hostname as
>unique identifer will no longer be able to associate the machine-specific
>state with the machine, effectively resulting in data loss.
>
>One example of the machine ID being used to identify hardware devices
>is that GNOME stores screen layout configuration keyed by machine ID,
>so that if you have an NFS-shared home directory or similar, it won't try
>to use your laptop's monitor layout on your desktop (or keep overwriting
>one layout with the other).
>
>One example of the machine ID being used to identify an OS installation is
>that if you use the systemd-boot EFI bootloader on a dual- or multi-boot
>Linux system (e.g. Debian and Fedora sharing a disk), systemd-boot stores
>each OS installation's kernel(s) in a directory named after the machine
>ID, so that they won't collide.
I have worked that information into the wiki page
https://wiki.debian.org/MachineId and appreciate your input.
Greetings
Marc
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