[systemd-devel] Environment for prefdm.service

[Bill Nottingham]

Lennart Poettering (lennart at poettering.net) said: 
> > Sorry if I'm missing something simple or if I have confused myself
> > beyond all hope.  I appreciate any advice on how to prepare this in a
> > future-compatible way.
> 
> My recommendation is to simply list display-manager.service in Alias= in
> [Install] in your unit file. Since that symlink can only point to one
> service we should be safe. The choice which one to start is done with
> this symlink and nothing else.

While this is correct, the issue we'd have off the top of my head
is if it's possible, in packaging, to have things automatically work
such that:

- installing multiple DMs gives you a predictable default
- removing whatever the current default is falls back to other DMs
  that are currently installed

Bill