Black screen to log on ubuntu


I have an Acer Nitro 5 AN515-44 with a processor AMD Ryzen 5 4600H and graphic cards GTX 1650 TI (4 Go) & AMD Radeon Vega 6.

When installing Ubuntu 20.04, at first i could’nt set luminosity of my laptop. I solved this problem by upgrading to the kernel 5.8.0-33 with command :

sudo apt install linux-generic-hwe-20.04-edge

Then i wanted to connect my laptop to my external monitor but it was not recognised at first. I finally solved my problem by adding Option “PrimaryGPU” “Yes” to the file /usr/share/X11/xorg.conf.d/10-nvidia.conf and by replacing Driver “amdgpu” with Driver “modesetting” to the file /usr/share/X11/xorg.conf.d/10-amdgpu.conf like this :

Section “OutputClass”
Identifier “nvidia”
MatchDriver “nvidia-drm”
Driver “nvidia”
Option “AllowEmptyInitialConfiguration”
Option “PrimaryGPU” “Yes”
ModulePath “/usr/lib/x86_64-linux-gnu/nvidia/xorg”

Section “OutputClass”
Identifier “AMDgpu”
MatchDriver “amdgpu”
#Driver “amdgpu”
Driver “modesetting”

But i just figured out by rebooting my laptop (without extetnal monitor connected) that Lightdm want to display HDMI instead of the screen of the laptop.
The consequence is the the screen of the laptop stays black on the login screen. Fortunaly, i can type my password (blind). Once password validated, the OS understand there is no monitor on HDMI and displays the screen of the laptop.
Important point, in Nvidia-settings the monitor number 1 is the external monitor, not the one of my laptop. And i can’t change it.

Does anyone already had this problem ?

Best regards,


With an amd/nvidia combo, rather upgrade to 20.10, it should support this ootb.

Thank you for your answer. I tried but i got the same issues about luminosity unfortunately…

You could try this:

I only have /etc/lightdm/lightdm-gtk-greeter.conf, no lightdm.conf
But there is something weird, all the lines begin with # which make commands inaoperate (comment) right ?

Those config files contain samples for possible setting which are therefore all commented out.
Just uncomment the needed setting or add them at the top of the file.