Bug#1107944: gdm3: use upstream 'gdm' for system user name instead of 'Debian-gdm'

[Simon McVittie]

On Tue, 17 Jun 2025 at 15:26:03 -0400, Jeremy Bícha wrote:
>According to debian/changelog, Debian began using the custom username
>Debian-gdm for the 'gdm' system user in gdm 2.30.5-7 in 2011

The big problem with having 'gdm' as a system user is that if your name 
is something like George David Miller, it's completely reasonable that 
you would want to use your initials, gdm, as your own login name. (And 
perhaps our users have already done so.)

Arguably the GNOME display manager's system user account should be _gdm 
(which would be the preferred name if gdm was being newly added to 
Debian, as per Policy §9.2) but that's no better than Debian-gdm in 
terms of whether upstream guides are going to work.

It's relatively normal for usernames and username policy to vary between 
distros - see also _flatpak (flatpak in many distros) and messagebus 
(dbus in many distros) - so anything that interacts with a different 
package's system user, for example gdm-setup, should expect to need a 
build-time option for the name of that user.

     smcv