Scaling issue with Nvidia Ubuntu

Problem

My laptop has a 4k screen and it has a Nvidia GPU and an integrated GPU, I want to conect to an external 1080p monitor via HDMI. The external monitor is recognized via xrandr and arandr, but it is over-scaled (not blurry, just too big). I cannot change the resolution of the second screen with xrandr --addmode as it always returns bad parameters.

Solution

Pre-requsite

• softwares

  • nvidia-prime

  • nvidia-settings

  • arandr

• make sure Nivida GPU is selected as prime with sudo prime-select nvidia, and check NVIDIA (Performance Mode) is selected in nvidia-settings. Then log-out and log-in again, run nvidia-settings, confirm there is a X Server Display Configuration option.

Procedures

The following procedures are required after every reboot:

1. run nvidia-settings and click X Server Display Configuration

2. select the external monitor and click Advanced in the bottom

3. modify ViewPortIn to 3840x2160 and click Apply

4. run arandr to adjust the layout

Important note

Although there is a Save to X Configuration File option in nvidia-settings (requires sudo to write the file), it will only save the external screen information, which means once reboot, only the external screen will be detected and the laptop screen cannot be used.

Therefore, do not save xorg.conf until I figure out how to modify the file to support multiple screens.