Change Linux Kernel Being Used

Refer: https://linuxhint.com/update_ubuntu_kernel_20_04/

Article originall written for Ubuntu 20.04 but used it with Ubuntu 18.04 to fix Parallels issue with slow startup

In order to downgrade to an earlier kernel you will need to make sure you can see the Grub boot screen and change things.

Refer: https://askubuntu.com/questions/82140/how-can-i-boot-with-an-older-kernel-version

At the time of this writing: 5.4.144 seems to work for Ubuntu 18.04
Base install of Ubuntu 20.04 used 5.8.0.63.71 and it seemed fine but upgrade to 5.11.0.36.40 seemed to slow bootup

5.8.18 works as of 2021-09-23, Parallels Tools do NOT seem to work with latest versions of kernel

Force remove, Seems Like Parallels is NOT ready for the new Kernels

Refer: https://askubuntu.com/questions/1253247/how-to-fix-or-remove-a-broken-kernel-ubuntu-20-04

cd /boot

Remove faulty links

sudo rm vmlinuz
sudo rm vmlinuz.old

Remove Faulty Kernel Example

sudo rm vmlinuz-5.7.5

Relink Correctly Example

sudo ln -s vmlinuz-5.4.0-37-generic vmlinuz
sudo ln -s vmlinuz-5.4.0-26-generic vmlinuz.old

Looking for Bad Stuff with 5.11 as Example

ll *5.11*

Final Cleanup to Take Changes

sudo update-grub
sudo apt update
sudo apt upgrade
sudo reboot now

Original Setup Starts Here

sudo gedit /etc/default/grub

change GRUB_TIMEOUT to -1 and comment out GRUB_HIDDEN_TIMEOUT

### GRUB_TIMEOUT_STYLE=hidden
GRUB_TIMEOUT=-1

Make sure you can see messages instead of splash screen

### GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
### GRUB_CMDLINE_LINUX_DEFAULT="noresume"
GRUB_CMDLINE_LINUX_DEFAULT=""
GRUB_CMDLINE_LINUX=""

sudo update-grub

Check your current version

uname -r

Install a GUI call "mainline" to install another kernel

sudo apt-add-repository -y ppa:cappelikan/ppa
sudo apt update
sudo apt install mainline

Select "mainline" from applications, and choose your kernel

After you download and build, you need to reboot

reboot

Check your new version

uname –r