[LightDM] Setting default X session

Yves-Alexis Perez corsac at debian.org
Mon Aug 29 00:56:07 PDT 2011

On lun., 2011-08-29 at 09:44 +0200, Didier Roche wrote:
> Le 13/08/2011 18:32, Yves-Alexis Perez a écrit :
> > On ven., 2011-08-12 at 08:27 +0200, Didier Roche wrote:
> Sorry for the late answer, but I was on vacations,

No problem. No CC: needed for me, I'm subcribed to the list, thanks :)
> This worked well with a gdm patch I made at the time between xubuntu, 
> ubuntu, ubuntu netbook edition, edubuntu and the whole ltsp environment 
> (which had other greeter need). Indeed, this require some work and 
> coordination between people but it prooved to be possible.

Yeah but cross-distro, cross-desktop is way bigger than “just” Ubuntu.
It might not be completely impossible, but that's a whole initiative
> >
> > 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).
> See /usr/lib/lightdm/lightdm-set-defaults --help, in particular:
>    -k, --keep-old     Only update if no default already set
>    -r, --remove       Remove default value if it's the current one
> Knowing that the lightdm policy is "if no greeter set in the 
> configuration file, do nothing" (no fallback). So, all depends on the 
> option set by the greeter. I would advise using --keep-old to not 
> overwrite the selection (without it, it updates the current value).

Well, with keep-old it's a bit useless at first sight. 

Right now, for greeters, I've added a bit of debconf magic so people can
chose the greeter at install or reconfigure time. I expect people
packaging other greeters in Debian to follow the trend. That is
something sustainable because it's only for Debian (and derivatives)
packagers, and only for few packages (lightdm greeters).

I don't think this can work for *all* DEs. And the first initiative
would be to have other DEs provide desktop files in /u/s/xsessions (see
recent mails to that list) and I'm not even sure those other DEs even
want that.

For me it's really important to:

* do something consistent when no session is chosen (like, not hang with
session half-run and no way to go back to the greeter)
* support legacy session startup where people put stuff to start
in .xsession

Another way would be to provide a way for the user to choose a session
not in the list. That would create a .desktop file
in .local/share/xsessions with data entered by the user, and set it as
the default in .dmrc.

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