Add a custom display resolution

Check available modes


If you need to add a mode you know, your hardware is capable of but isn't listed, you can add it manually.

In a terminal generate the modeline

cvt 3840 2160 30

The output should look something like this

Modeline "3840x2160_30.00"  338.75  3840 4080 4488 5136  2160 2163 2168 2200 -hsync +vsync

Now add that mode to the X server

xrandr --newmode "3840x2160_30.00"  338.75  3840 4080 4488 5136  2160 2163 

Add the new mode to an output

xrandr --addmode DP-1 3840x2160_30.00

And set it the same way as above

xrandr --output DP-1 --mode 3840x2160_30.00

Note that setting the resolution is not permanent.
To make it permanent, add all three lines (--newmode, --addmode and --ouput) to ~/.config/openbox/autostart.