Ubuntu full install to USB won't boot updated kernels

Question

I did a full install of the latest Ubuntu desktop to a USB stick using the instructions at How to Create a Full Install of Ubuntu 20.04 to USB Device Step by Step and it boots fine

However, if I download and install the latest kernel from say https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.13-rc7/, grub2 still boots v5.11.0-18

I'm doing this because I need some new drivers. Do I need to copy boot files again as in the original install? Or is there something else like this image is unsigned and therefore doesn't even show up in grub's advanced menu even though update-grub saw all the kernel images?

Thanks

Answer 1

Ubuntu Full Install to USB - Updated Kernel

Upgrading Ubuntu's kernel should add the new kernel to sdx4/boot/grub/grub.cfg menuentry.

sdx3/boot/grub/grub.cfg is not updated automatically.

Check sdx4/boot/ to confirm vmlinuz-5.13-rc7 and initrd.img-5.13-rc7-generic exist. If not reinstall the new kernel.

Check sdx4/boot/grub/grub.cfg and sdx3/boot/grub/grub.cfg to confirm vmlinuz-5.13-rc7 and initrd.img-5.13-rc7-generic are noted in the first menuentry of each cfg file.

I think that you probably need to copy grub.cfg from partition sdx4/boot/grub/ to partition sdx3/boot/grub/overwriting that grub.cfg file one more time as is required when doing a sudo update-grub.

if vmlinuz-5.13-rc7 and initrd.img-5.13-rc7-generic are not specified in either sdx3 or sdx4 GRUB, the cfg files should be backed up and edited changing 5.11.0-18 to 5.13-rc7 or whatever the latest kernel in boot is named.