How to bring kernel 5.8 back on 20.04

I've been using Ubuntu 20.04 in a very old computer (with a very old nVidia card) for a long time without problems, until it was automatically updated to Kernel version 5.13.

I don't know what, but something is definitely broken in the Kernel 5.13 that causes several issues:

• nVidia card not working correctly (can't login to desktop, screen stays completely blank).
• form time to time the filesystem automatically goes into read-only mode and the only solution is to reboot the machine.

I didn't spend much time looking for solutions to those issues, because I still had the option to boot using Kernel 5.8, which worked perfectly.

But now Kernel 5.8 disappeared from Grub's list, and it only allows me to choose between 5.13 versions.

How can I bring Kernel 5.8 back and prevent automatic upgrades from removing it?

You can reinstall kernel 5.8 by running the following command but that really won't fix your problem.

sudo apt install linux-image-5.8.0-63-generic linux-headers-5.8.0-63-generic

After you reboot, kernel 5.8 will be available in your Grub menu. Most likely, you ran sudo apt autoremove or something similar which removed the older kernel version as the linux-image-generic-hwe-20.04 package changes dependencies when a newer kernel is released.

To search for packages, you can use:

apt-cache search linux-image-5.8
apt-cache search linux-headers-5.8

and to narrow the results, you can use grep:

apt-cache search linux-image-5.8 | grep generic
apt-cache search linux-headers-5.8 | grep generic

But you really should install the proprietary Nvidia driver using:

sudo ubuntu-drivers autoinstall

to prevent problems with upgrades.