On Thu, 8 Aug 2019 22:59:05 +0100, Simon McVittie <s...@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 -- -------------------------------------- !! No courtesy copies, please !! ----- Marc Haber | " Questions are the | Mailadresse im Header Mannheim, Germany | Beginning of Wisdom " | Nordisch by Nature | Lt. Worf, TNG "Rightful Heir" | Fon: *49 621 72739834