[LightDM] Setting default X session

[Yves-Alexis Perez]

On ven., 2011-08-12 at 08:27 +0200, Didier Roche wrote:
> 
> Package should in their postinst call this one to set themselves as 
> default (using the --keep-old options) and remove them on 
> install/removal. For instance:
> http://launchpadlibrarian.net/76923334/gnome-session_3.1.3-0ubuntu9_3.1.3-0ubuntu10.diff.gz
> to set the default session to "ubuntu" for the ubuntu desktop case.
> and:
> http://launchpadlibrarian.net/76923333/unity-greeter_0.0.2-0ubuntu1_0.0.2-0ubuntu2.diff.gz
> for the greeter.
> 
> So basically, installing them will set the first installed one (we don't 
> expect having multiple greeters in a CD spin for instance) as the 
> default. Then, casper has now a fix for just adding the autologin part 
> without hammering those things:
> http://launchpadlibrarian.net/77000287/casper_1.277_1.278.diff.gz
> 
> Please note that this is very similar to the patches I made for gdm back 
> in the lucid days (10.04) which seems to have fit the numerous flavors 
> and derivatives we have.

This might work in Ubuntu, but I don't expect each and every “desktop
environment” (including window managers) to do that. That might work as
a best effort (like I could do this in Xfce) but not for a whole
distribution like Debian.

And even with that, what happens when:

* desktop A is installed, setting the default session to A
* desktop B is installed, setting the default session to B (old default
to A)
* desktop C is installed, setting the default session to C (old default
to B)
* one of them is removed

Who is the new default, and why? I don't think there's a way to have a
really consistent situation (and one which would fit the user).

So all in all, I think that managing the default with alternatives,
which is an existing, working system which does exactly the same kind of
thing you tried to fix, might be the best way we have. It's not perfect
(the whole priority thing and the fact it's Debian-based) but it can
work.

Regards,
-- 
Yves-Alexis
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