Sometimes Kubuntu does not show the correct resolutions (I suspect Intel GPUs have something to do with it.). If we wanted to add 1280×800 al monitor LVDS1 (xrandr --current to see the name of your monitor), we generate synchronization times with cvt: $ cvt 1280 800
# 1280x800 59.81 Hz (CVT 1.02MA) hsync: 49.70 kHz; pclk: 83.50 MHz
Modeline "1280x800_60.00" 83.50 1280 1352 1480 1680 800 803 809 831 -hsync +vsync
We add the resulting Modeline to xrandr:$ xrandr --newmode "1280x800" 83.50 1280 1352 1480 1680 800 803 809 831 -hsync +vsync
We add it to our screen, and we activate it:$ xrandr --addmode LVDS1 1280x800
$ xrandr --output LVDS! --mode 1280x800