Bdtyktl

After apt-get upgrade and a normal shutdown of my Ubuntu installation (I do have a Windows 10 installation as well) I suddenly cannot boot Ubuntu anymore. It is not even possible to Ctrl-Alt-Fx to another console.

Adding the nomodeset boot options at least enables me to log in a console. startx terminates immedeately.

Disabling Wayland in /etc/gdm3/custom.conf also did not help.

"failed to start user manager for uid 121"

is appearing in the syslog.

What also happened recently is that I added a third screen to my setup and it was the first time that Ubuntu booted with the screen connected (albeit switched off). It it possible that this somehow corrupted my xorg.conf? Is there a way to revert whatever went wrong?

The general behavior reminded me of this bug but I am not sure if the issues are related.

Edit:
the syslog shows the following

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: (II) VESA(0): Setting up VESA Mode 0x1D4 (3840x2160)

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: (II) VESA(0): VBESetVBEMode failed, mode set without customized refresh.

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: (==) VESA(0): Default visual is TrueColor

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: (==) VESA(0): Backing store enabled

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: (==) VESA(0): DPMS enabled

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: (==) RandR enabled

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: (II) SELinux: Disabled on system

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: (II) AIGLX: Screen 0 is not DRI2 capable

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: (EE) AIGLX: reverting to software rendering

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: (EE) AIGLX error: amdgpu does not export required DRI extension

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: (EE) GLX: could not load software renderer

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: (II) GLX: no usable GL providers found for screen 0

a little bit further down the line:

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: amdgpu_device_initialize: amdgpu_get_auth (1) failed (-1)

and finally

Feb 18 22:52:11 mycomputer gnome-session-binary[1923]: Unrecoverable failure in required component org.gnome.Shell.desktop

Feb 18 22:52:11 mycomputer /usr/lib/gdm3/gdm-x-session[1911]: gnome-session-binary[1923]: CRITICAL: We failed, but the fail whale is dead. Sorry....

Next edit:
After uninstalling the amdgpu-pro drivers (amdgpu-pro-18.50-708488-ubuntu-18.04) and replacing them with the newest version (amdgpu-pro-18.50-725072-ubuntu-18.04), everything is working as expected again