How can I investigate the cause of total hang? Is there some information that I should pay attention to in order to get some hint?

[Oleg Cherkasov]

On 02.07.2020 15:58, Mike Marchywka wrote:
> 
> You could try unplugging anything plugged in and plugging it back in.
> Maybe even plugging in a second keyboard. Although probably deadlock
> or just a simple crash.

Very good suggestion indeed to unplug all USB devices if possible.  I 
had few times a problem with an external USB disk.  It started to fail 
and endless re-syncing almost hang my system so it way nearly unresponsive.

BTW does "Magic SysRq" work as expected after the system hangs?