If you connect your laptop or netbook to a monitor in ubuntu, resolution may be in lower rift, but you can correct this value by typing

xrandr –output VGA1 –auto
xrandr –output LVDS1 –off –output VGA1 –mode 1152×864 (Example)
xrandr –output LVDS1–off –output VGA1 –mode 1280×1024 (Example)

So you can reach the correct resolution to solve this problem in an easy manner.