Unity greeter doesn't show other desktop environments, yet allows login to Unity

[David Ing]

On Ubuntu 16.04, I followed instruction to install KDE Plasma via the Backports PPA. This didn't work out well. I have been in the process of removing that installation. The Unity greeter looks normal on launch, and will let me log in to Unity as usual.

However, when I try to select another desktop environment, that panel goes blank so that there's no place to log in.

Selecting shutdown from the upper right panel doesn't work. I have to turn the laptop over and pull the battery to restart.

A similar problem was reported as "Selecting other session in login screen doesn't do anything" for Ubuntu 12.04 at https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/918072 . This suggests a workaround to ..

> Edit /etc/lightdm/lightdm.conf (sudo gedit /etc/lightdm/lightdm.conf), changing
> greeter-session=unity-greeter
> to
> greeter-session=lightdm-gtk-greeter

... which does show the alternative desktop environments for login.

I appreciate that Unity has been announced are stabilized in future Ubuntu releases. If unity-greeter will no longer be supported, what greeter will be used in future releases?

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: lightdm 1.18.3-0ubuntu1.1
ProcVersionSignature: Ubuntu 4.4.0-75.96-generic 4.4.59
Uname: Linux 4.4.0-75-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
CurrentDesktop: Unity
Date: Tue Apr 25 10:58:56 2017
InstallationDate: Installed on 2014-04-19 (1101 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
LightdmConfig:
 [SeatDefaults]
 greeter-session=unity-greeter
SourcePackage: lightdm
UpgradeStatus: Upgraded to xenial on 2016-09-17 (220 days ago)