I had several programs running on a server, which I connect to with VNC Viewer. And for some reason firefox became unresponsive, and the screen froze. I followed these steps:
vncserver kill -9 :1
to kill the processvncserver :1
to start a new onesudo reboot
However, when I reconnected, the screen was still frozen and I could not even move the mouse cursor. Here is a screenshot:
Whoops! I found the reason for that, I had mistakenly checked the view-only checkbox. Here is the screenshot: