So I am currently messing around with a tiling window manager on my laptop – I prefer tiling window managers in general (I use Awesome on my main desktops). These are (in general) not “desktop environments” but just manage windows (and sometimes a “status bar”).
As it happens the window manager I’m messing with doesn’t come as part of a distribution package with a pre-prepared file for GDM3 to use. So I created a ~/.xsession file – something that has worked since display managers first arrived.
Turns out that I need to “hack” GDM3 to make a long standard bit of functionality functional again. As an aside (and especially to the GNOME people), all you had to do to keep this functional was detect if someone had a ~/.xsession file and then offer that up as a menu option. Not that difficult to do and even if it isn’t your preferred way of doing things, it’s a nice thing to do for us old-timers.
Anyway, to restore this functionality all it took was to create a file in //usr/share/xsessions/ called xsession.desktop with the following contents :-
[Desktop Entry] Name=XSession Comment=This session uses the custom xsession file Exec=/etc/X11/Xsession Type=Application DesktopNames=GNOME-Flashback;GNOME; X-Ubuntu-Gettext-Domain=gnome-flashback
And yes I stole this and adapted it myself – I’m putting this up here so that I know where to look when I need it again.