|Phew ... all's well that ends well.|
Had this error: "Ubuntu: failed to connect fo lvmetad". Ubuntu booted into a shell. The /home partition was not mounted. I tried to edit the fstab, but the /home share would not mount on boot.
However it was possible to mount the drive, like:
# mount -a
In the failsafe Ubuntu version I cound boot into a menu, with several options. If a fsck was run, the /home would mount, and the boot process could continue.
An error message stated, that there was an error on the /dev/sda5 - and Ubuntu recommended a "manual fsck".
So I booted into the shell, and ran fsck. There were tons of errors, Basicly the prompt asked "shall I repair this or that error". I answered "y" every time. Fsck found some 30 - 40 errors. Then fsck stated, that the system was clean.
I booted ... and ...
to my great surprise everything worked. As in: OK!
During the failsafe mode the CPU ran like hell: 50% or more all the time. The temperature was not a problem. But of course the fans ran like hell. Now everything is back to normal. The CPUs run around 20% when I use a browser, Spotify and what not.
So we're back to normal after a weird trip to shell-land.