Frozen Screen

cases very likely happen when Ubuntu unexpected stopping a program.

to make it work normally, the culprit process has to be forcedly stopped.

solution 1

press Alt + F2, type xkill, use mouse close it

solution 2

open terminal, find its PID, then kill [PID], by using command ps aux | grep [program-name], showing on second column.

note, another feature command pgrep is alway available to directly show PID.

in wired scenario, this PID is not correct one that we want, so better use top command to find it.

solution 3

relog in, by Alt + Ctrl + F1, restart the service, sudo service lightdm restart