Using xrandr to change screen resolution and orientation

X RandR is a useful tool to configure display ports, display modes and properties such as orientation, reflection and DPI.

Some simple usage of xrandr
$ xrandr -v (Server reports RandR version 1.3)
$ xrandr -q (query what screens are connected)
$ xrandr -s 1280x800 (screen resolution)
$ xrandr -o inverted (orientation inverted, left, right, normal)

Do note that for xrandr -0 , your screen might freeze after the command, you may want to use xrandr --verbose to check the error.

To extend xrandr to utilise and join 2 monitor together, you may want to look at http://www.thinkwiki.org/wiki/Xorg_RandR_1.2 for more information