xrandr: RandR (Resize and Rotate) X Window System extension.

Some useful commands:

xrandr --listmonitors
cvt 1600 1200 60
xrandr --newmode "1600x1200_60.00" 161.00  1600 1712 1880 2160  1200 1203 1207 1245 -hsync +vsync
xrandr --addmode "HDMI-1-1" 1600x1200_60.00

If you encountered the following error:

xrandr xrandr: Failed to get size of gamma for output

it may be caused by a bad graphic card driver. In my case, a dummy driver instead of the official NVIDIA driver.