Things appear to have changed from 14.04. Then, my last desktop environment was remembered and I did not have to select one each time from the greeter login. One user defaulted to cinnamon, another to ubuntu (unity).

With 15.10, the greeter login ALWAYS defaults to ubuntu. /usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf contains:

[Seat:*]
user-session=ubuntu

and this always appears as the default selection, even though $HOME/.dmrc for a user contains:

[Desktop]
Session=cinnamon

I suppose I can make the default ALWAYS e.g. cinnamon by changing 50-ubuntu.conf, but that still doesn't give me a per-user default. It seems like the current implementation renders $HOME/.dmrc useless.

Is there a way to set a per-user default for desktop environment with 15.10?

(btw - I've asked 5 questions in askubuntu.com over the past 2 months, none of which have been answered there, all of which have been answered in LQ. Guess where my go-to forum for Ubuntu question is from now on!)

Have you installed both desktop enviroments?

unity comes installed and yes, I've installed Cinnamon. I can select it from the lightdm login box. For now, I've modified /usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf to set cinnamon s the default, but as I said, this does not facilitate setting the desktop per user (as I'm sure I did with 14.04) and it appears that $HOME/.dmrc is completely ignored ion 15.10.