Bug#241096: little hack

[Josep Puigdemont]

Here is a hack that will only work for a particular user to log in into
gnome after authenticating with GDM (I suppose it would also work for
XDM or after doing 'startx').
GDM will still miss all entries you might have in directory Sessions.

Iirc, GDM will search for a default session if the user has no .xsession
file in its home directory, so I solved my problem by including the
following line in .xsession:

exec gnome-session

(the file didn't exist, so I created it)
There might be something similar for kde, etc...

Hope it helps!