Thinkpad P54 with Ubuntu 20.04 - Nvidia driver problems

In a previous article I installed Ubuntu 20 and everything works fine. But after last update, few days of using there was a problem with nvidia drivers.

Reinstall and prime switching, removing X11 nvidia config didn't worked for me. Maybe just my bad usage (I used to run other Kernel), but I will show you my way to solve all problems.

During reinstallation of nvidia drivers I noticed, that drivers was installed only for Generic Kernel. So fast check:

$ uname -r
5.4.0-26-lowlatency

Whaat?! I have no idea why, I though that by default is always generic. I never changed it!

Ok but I don`t need lowlatency so I checked my available images:

$ dpkg --list | grep linux-image
ii  linux-image-5.4.0-21-generic                 5.4.0-21.25                                amd64        Signed kernel image generic
rc  linux-image-5.4.0-24-generic                 5.4.0-24.28                                amd64        Signed kernel image generic
rc  linux-image-5.4.0-24-lowlatency              5.4.0-24.28                                amd64        Signed kernel image lowlatency
ii  linux-image-5.4.0-25-generic                 5.4.0-25.29                                amd64        Signed kernel image generic
ii  linux-image-5.4.0-25-lowlatency              5.4.0-25.29                                amd64        Signed kernel image lowlatency
ii  linux-image-5.4.0-26-generic                 5.4.0-26.30                                amd64        Signed kernel image generic
ii  linux-image-5.4.0-26-lowlatency              5.4.0-26.30                                amd64        Signed kernel image lowlatency
ii  linux-image-generic   

First I checked linux-image-5.4.0-26-generic by running it from Grub menu (Advanced options). Everything worked fine, except that now my laptop monitor was disabled, and only external monitor works on nvidia. For that just erase whole xorg.conf, don't remove (Im not sure if you can), just leave it empty:

/etc/X11/xorg.conf

After reboot (still have to select right Kernel from advanced Grub menu) it finally worked fine.

Last I need to set this Kernel to boot by default. I don't want to select right one every time. Fastest way to do it is to edit:

/etc/default/grub

I had GRUB_DEFAULT=0, so I changed this option to:

GRUB_SAVEDEFAULT=true
GRUB_DEFAULT=saved

Updating Grub after editing:

$ sudo update-grub

Now Grub remember my last used kernel. After first reboot select again desired Kernel, because saving option will work after reboot. Second reboot works fine.