Comment 8 for bug 1571564

ALT+F2 opens KRunner - It's ALT+CTRL+F2 _this opens a virtual Console (TTY2) to return you press ALT + F7

Some people call this rescue-console

In TTY2 you could just login username: kubuntu password: just leave it blank

Once you are loooged in type "startx" (w/o marks)

Then you could toogle to /var/log/

interesting would be gpu-manager.log

Someone on the german ubuntutuusers.de forum wrote in the Ubuntu+1 channel that it worked flawless as he being on a hybrid graphics machine activated the hybrid-graphics mode in the UEFI-Bios - not knowing if he ticked the "install third-party drivers" or if he just relied in Nouveau+Intel-XOrg drivers