xrandr (use "xrandr --output <output> --rotate (normal|right|left|inverted)", e.g. "xrandr --output DVI1 --rotate right") Ubuntu also has a graphical tool for

xrandr (use "xrandr --output <output> --rotate (normal|right|left|inverted)", e.g. "xrandr --output DVI1 --rotate right") Ubuntu also has a graphical tool for this, probably also other distributions.