Thanks for all the replies to the Error Messages.
I don't know how you find which disk is referred to by ata5.
I think dm-0 is a reference to a Raid setup.
Other information about my hardware and rebooting :-
I have two 1 TB hard drives arranged as a RAID 1 array.
The power supply :-
Corsair TXM Gold 550 W 80+ Gold Certified Semi-modular ATX
About 18 months old.
Motherboard BIOS :-
Someone else was checking the BIOS. They said it was a Beta version. I discovered my RYZEN 5 5600x is the stepping 0
version of the CPU.
Ram :-
I don't know the make of the Ram - someone built the PC for me.
16GB DDR4-3200MHz RAM (2 x 8GB sticks, I understand
Reboots :-
Subsequent to those error messages, I tried a reboot.
This failed :-
The reboot error says:
/dev/mapper/vgpiglit-root contains a file system with errors, check
forced.
Inodes that were a part of a corrupted orphan linked lost found.
/dev/mapper/vgpiglit-root : UNEXPECTED INCONSISTENCY; RUN fsck
manually.(i.e .,
without -a or -p options). fsck exited with status code 4. The root
filesystem on /dev/mapper/vgpiglit-root requires a manual fsck
There is then a flashing prompt after "(initramfs)".
The fsck command was then performed :-
fsck -y /dev/mapper/vgpiglit-root
A subsequent reboot worked.
Firefox then had a very lengthy cursor lag, but this was solved by deleting the places and favicons data in the Firefox profile.
No more error messages yet.