Problem running Ubuntu 20.04 kernels

Seems to be a UEFI thing
https://bbs.archlinux.org/viewtopic.php?id=226803

I suggest you report a bug. You can boot old kernels by holding SHIFT at boot then choosing the older kernel

A possible reason for such message could be a failure during the update.
What are the version numbers of the failing and the working kernels?

What is the output of
ls -l /boot

The installed kernels are:
                                                           - 5.4.0-42-generic (default install)
                                                           - 5.4.10-rt5
                                                           - 5.8.0-41-generic (default install)

For each version are present the corispective files vmlinuz, System.map, initrd.img and config-5...

I have to use the 5.4.10-rt5 version, i tried this version on virtual machine and work.

I tried other version such as 5.1.13, 5.5.0 (also not RT kernel) and these also present this error.

I'm doing other tries now.

thanks

Now i tried the version 5.9.0-rt5 and in this case i have another error:

error: can't allocate initrd
x86/cpu VMX (outside txt) disabled by BIOS

the errors change

Please provide the _full_ output of the commands

uname -a
lsb_release -crid
ls -l /boot

This is the full output:
https://drive.google.com/file/d/1Yv-yTnPkSC_h5JQWhFJJASMpqQKSPijR/view?usp=sharing

Why didn't you just copy/paste the text into this question document? This would have been much easier for us.

Where did you get the *rt* kernels? As far as I know they are not provided by standard Ubuntu.

Wich one of the four versions does work and which one doesn't?
5.4.0.42-generic
5.4-10-rt5
5.8.0-41-generic
5.9.1-rt20

Because I'm using another PC, sorry.

I took the *rt* kernels of the site : https://www.kernel.org/pub/linux/kernel/projects/rt/ indicated of the linux kernel archives site.

Yesterday I tried not rt version and i got the same error.

The versions that work are: 5.4.0.42-generic and 5.8.0-41-generic (default install).

The versions that not work are: 5.4-10-rt5 and 5.9.1-rt20.

All version work on virtual machine of another PC.

This is support for Ubuntu, and the Ubuntu kernels work well, only those from a foreign source don't.
So this is not an Ubuntu problem and hence not really the right place.

"x86/cpu VMX (outside txt) disabled by BIOS"
Have you checked the BIOS of the system, if there is a switch to enable this?

Do you have the newest version of the BIOS available for your system?

I tried with VMX enable but is don't work.

The BIOS isn't updated.

Thanks everyone for the help.

I solved the problem.

The image wasn't being loaded because the size was too big.
After reducing the size the new kernel is work.

Best regards