How to configure a 4k screen in Linux
Troubles with your screen?, here is how to fix it.
You just got a new cool 4K monitor, you opened it, connected it to your Linux device and the first thing you face is that you can’t select the maximum resolution for the screen.
My disappointment is immeasurable and my day is ruined. —Reviewbrah
Why is this problem happening?
Apparently some screens might not give the correct EDID information, in my case a SAMSUNG LU28E85KRS, this makes it impossible to select all supported modes for our screen, showing some default ones, without including resolutions greater than 1920x1080.
How to get the correct EDID and set it using xrandr
Getting the correct EDID
Thanks to this wonderful answer How to get EDID for a single monitor? by Malat, obtaining the correct information is easy.
sudo apt install read-edid
sudo get-edid | parse-edid
Cool, we get all supported modes.
Modeline "Mode 1" 148.500 1920 2008 2052 2200 1080 1084 1089 1125 +hsync +vsync
Modeline "Mode 0" 297.00 3840 4016 4104 4400 2160 2168 2178 2250 +hsync +vsync
Modeline "Mode 2" 74.250 1280 1390 1420 1650 720 725 730 750 +hsync +vsync
Modeline "Mode 3" 148.500 1920 2448 2492 2640 1080 1084 1089 1125 +hsync +vsync
Modeline "Mode 4" 74.250 1280 1720 1760 1980 720 725 730 750 +hsync +vsync
Modeline "Mode 5" 27.027 720 736 798 858 480 489 495 525 -hsync -vsync
Modeline "Mode 6" 27.000 720 732 796 864 576 581 586 625 -hsync -vsync
Modeline "Mode 7" 74.250 1920 2558 2602 2750 1080 1084 1089 1125 +hsync +vsync
Modeline "Mode 8" 74.250 1920 2008 2052 2200 1080 1084 1089 1125 +hsync +vsync
Modeline "Mode 9" 148.50 1920 2008 2052 2200 1080 1084 1089 1125 +hsync +vsync
Modeline "Mode 10" 148.50 1920 2448 2492 2640 1080 1084 1089 1125 +hsync +vsync
Modeline "Mode 11" 74.25 1280 1390 1430 1650 720 725 730 750 +hsync +vsync
Modeline "Mode 12" 241.50 2560 2608 2640 2720 1440 1443 1448 1481 +hsync -vsync
Adding the new modes with xrandr
The first value after the mode number tell us the horizontal resolution, in my case I’m interested in Mode 0.
Modeline "Mode 0" 297.00 3840 4016 4104 4400 2160 2168 2178 2250 +hsync +vsync
Let’s create a new mode, we can name it anything we want, but I prefer to name it after the output resolution.
xrandr --newmode "3840x2160" 297.00 3840 4016 4104 4400 2160 2168 2178 2250 +hsync +
Now we add the mode to the output, if you are not sure which one is the output, run xrandr and it will show something like HDMI-2 connected.
We use the name of the output.
xrandr --addmode HDMI-2 3840x2160
Now the new resolution should be available in the Display settings.
Don’t forget to set font DPI and screen scale to you taste.