I have Ubuntu 16.04.2 LTS, with kubuntu-desktop installed as well as ubuntu-gnome-desktop. The problem is that I cannot switch between Unity, Plasma, and Gnome. When I click the switcher, it does not show any desktop environments and defaults to Gnome. When I try to install Unity, which apparently has been uninstalled, it gives me a "you have held broken packages" error. The login is also quite broken, as it requires multiple tries to log in. In short, I might have irreversibly damaged my computer.

  • I have a feeling this is a problem with multiple display managers (lightdm, gdm, kdm etc...) you can try sudo dpkg-reconfigure lightdm (or gdm, etc..) and set a default display manager. – nullmeta Apr 23 '17 at 19:06
  • gdm3 and sddm work for the switcher. It seems that the problem lies with lightdm. – Sean Zheng Apr 25 '17 at 0:44
  • Glad to hear it, I had a similiar issue and lightdm was my problem too. It doesn't seem to want to play nice with the others. – nullmeta Apr 25 '17 at 0:47

You can set a different default display manager using

sudo dpkg-reconfigure lightdm

(or gmd3, kdm, sddm, etc...)

Changing the default manager should work to restore the switcher functions. It seems lightdm does not like to play well with others.

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