blue and white progress bars were making their way across the screen. I do not know howto capture the stacktrace. The machine freezes. Ctl-Alt-Del does not cause a reboot. The offswitch does not work.
If the box goes castors up it's fairly hard to capture it. You pretty much have to write it down (or take a photo of it) and transcribe it later.
The photo is actualyl a pretty good approach as you can then reboot the system and get it back in service fast.
Alan