LightDM doesn't show desktop session lists

Question

Before upgrading to Ubuntu 16.04 from 14.04 I used to log into GNOME-flashback desktop session from GDM login prompt. After upgrading to Ubuntu 16.04 I had to remove GDM(along with nvidia proprietary drivers etc.) as it never starts(gets stuck at systemd prompt) and installed LightDM again. It was going on without further problem since then until today I tried to change the session to GNOME-shell from LightDM.

I clicked the desktop session chooser button at top-right of the little login box provided by LightDM greeter screen and it gave me a blank box instead of a list of desktop sessions. I managed to bring back the password prompt by clicking on hostname on the top left of the screen. But now I can only log into GNOME shell.

The steps I tried without success

• Listing out possible desktop environments

  $ ls /usr/share/xsessions/
  gnome.desktop                   gnome-flashback-metacity.desktop
  gnome-flashback-compiz.desktop  ubuntu.desktop
  

• manually creating a (possibly deprecated) /etc/lightdm/lightdm.conf with following content

  [SeatDeafults]
  user-session=gnome-flashback-compiz
  

  and subsequently after it didn't work

  [SeatDeafults]
  user-session=gnome-classic
  

• editing ~/.dmrc(which was present in system before this problem)

  [Desktop]
  Session=gnome-classic
  Language=en_US.UTF-8
  

So now I'm stuck with GNOME shell as the only desktop environment. I want to go back to GNOME classic session and want to be able to switch between desktop environments when needed. Any help on this?

Answer 1

I guess your unity-greeter has messed up something. I have two solutions.

• Reinstall it

  sudo apt-get --purge autoremove unity-greeter
  sudo apt-get install unity-greeter
  

• Or Install lightdm-gtk-greeter instead. Install it with

  sudo apt-get install lightdm-gtk-greeter
  

  and change it as default using

  sudo update-alternatives --config lightdm-greeter
  

  and select the entry for lightdm-gtk-greeter and pressing Enter.