On the upgrade from 11.10 to 12.04, my XMonad + Unity configuration no longer works. When I attempt to log into this session, I get "failed to load session 'xmonad'". Where can I look to figure out what's going wrong?
What worked for me was to remove the references to
unity-2d-launcher entirely from my
/usr/share/gnome-session/sessions/xmonad.session (which I had configured for 11.10 the way Mark Hansen suggested):
[GNOME Session] Name=Xmonad Unity RequiredComponents=gnome-settings-daemon; RequiredProviders=windowmanager;panel; DefaultProvider-windowmanager=xmonad DefaultProvider-panel=unity-2d-panel
I always use the shellPrompt instead of the unity launcher anyway, so I don't miss the launcher at all.
I was able to get the XMonad + Unity configuration to work. I examined the relevant configuration files in /usr/share/xsessions/ and /usr/share/gnome-session/sessions/ (for more info see http://markhansen.co.nz/xmonad-ubuntu-oneiric/), and tried to run the various executables they reference. I thus discovered "gnome-panel" had been uninstalled on the upgrade, so I reinstalled it.
Possibly relevant: I recently upgraded and found I needed to delete the file
~/.xmonad/xmonad-x86_64-linux, and all was fine. I run gnome + xmonad, but this step is relevant to any upgrade. See here for more notes on my experience.