kernel update - restart(required) failed to mount "/"

This is the 2nd kernel update on this old HP Compaq desktop that has exhibited this problem AFTER the required restart.
(I will see what happens on the laptops tomorrow).

After the required restart, It connects to the internet, then I get that ugly big red symbol popup that says 'failed to mount directory at /"
Nothing would accept mouse clicks.
I tried to open Dolphin and it didn’t. I couldn’t get to a terminal to do anything there either, SO, I clicked the panel to shutdown, and it didn’t accept the mouse click.

I had to shutdown the bad way by pressing the power button on the tower.
Then started the boot again, and this time things worked as ‘normal’(whatever that is?).

Also after the last 2 kernel updates things seem to be a bit slower in responding in general to mouse clicks and keyboard commands.

IS it possible my hardware is getting past a supported limit for the newer kernels?

This may sound a bit duff, but I read this as that you first did the “required restart”, which did result in problems after login.
Then you did a power down and start again which worked without problems.

This makes me into mistrusting the quality of your first “required restart”. Better do a shutdown with power off next time after a kernel update?

A restart is supposed to reset the hardware. A power off may reset more than a restart.

You might be seeing an issue with something not properly resetting on restart. And yes, that could be due to aging hardware. And aging power supply might be providing a bit less than the needed voltage (for example).

After the updates(usually more than 1) have completed, the update notification (with the 'Requires Restart) is still on the screen, and has a ‘RESTART’ switch on it. I click that to do the restart. It doesn’t go all the way to complete power down, but does get to the HP logo, then BIOS screen, then the GRUB selection screen.
I only had to power down after the initial RESTART with the PC’s power switch because whatever happened locked the system to the point of no action trying to do anything!

BTW, I do the same on both laptops, and neither of them have ever exhibited this failed to mount error after a RESTART using the restart switch on the notification panel.

I changed out the power supply 2 years back for a more powerful one(I forget the specifications), so it’s new. The MOBO is not, and the memory chips have been upgraded with in the last 8 years. I added my own graphics card and bypass the onboard graphics & I added an Ethernet card capable of 1000/100/10(again bypassing the MOBO Ethernet 100/10).
I admit the Compaq CMT DC7700 is old, but only the MOBO is original.

It was just because the strange behaviour you reported that I made a wild suggestion. But indeed, as you say that you even see the HP logo, etc., it must have been a reboot.

What I see as the most strangest about this is that it reports a not mounted / way after the system has booted (which is impossible without a mounted /) and only when you have already logged in (because you report a pop-up and that can only happen in a GUI, thus somebody must have logged in in the GUI and got a desktop).
Strange sequence.

yes, I got a desktop, the desktop was almost complete & it showed internet connection was made, and immediately after that that pop up with a large RED box with an exclamation in it with the warning about ‘directory @ / could not be mounted’.
And I could not do anything with keyboard or mouse.
It happened so quickly, and that pop up lasted maybe 5 seconds(IMO it SHOULD stay)!
Next time(hopefully there won’t be a next time) I will try to get a picture of it with my iPad.

Could/would a CMOS battery cause that kind of situation? It has never been changed.

As you describe it, it seems to be something that either only happened once, or irregular. That could mean (and I assume it means) that there is no real connection with the fact you re-booted because of the new kernel.
Indeed, waiting if it happens again seems to be the best now.

No idea. I assume you would see more strange things then.

You can never tell unless you change the battery, which is easily done.

In most cases puzzling behavior is related to memory: https://forums.opensuse.org/showthread.php/547390-Puzzling-Keyboard Errors won’t show up immediately. You may want to run memtest overnight for a week.

OK, come on over and do it! Kidding.
The battery is buried on the board between two PCI cards, and really hard to get to without removing at least two of the cards. I may tackle that if I start seeing strangle things on PC start up.

Another kernel update last night, and this time I did a full shutdown and boot
instead of clicking on that RESTART panel the update leaves on the screen
(yes I could dismiss it but it is a reminder)
A clean ‘restart’ was made and I didn’t get that ‘failed to mount /‘ pop up message.
We’ll see what happens with future updates requiring a ‘RESTART’.

THANKS FOLKS, I appreciate all of the comments help and support!

I use a Phillips #2 screw driver for everything but m.2 drives, which require a smaller tool: List of screw drives - Wikipedia Removing the battery with the screw driver works fine on my boards. If it doesn’t on yours use the screw driver to remove the cards and try again.

Perhaps drive failing? Did you check it, with smartd or similar?

Just an idea.