When your monitor's resolution isn't automatically detected properly, here are instructions for fixing it.

This has worked for me in Ubuntu Unity, Gnome 2, lots of places.

try to read the monitor's EDID

force it to use an unlisted resolution

Use xrandr for this. An example that I use for dual-heads on my laptop:

GUI tools that can be used for this: arandr (deb), grandr, gnome-randr-applet, zarfy, lxrandr

make the change permanent

Xrandr makes changes dynamically, so it's useful if you frequently plug/unplug a monitor. If you want to make things permanent, use xorg.conf.

try this first

Specifying the resolution for individual monitors in xorg.conf:

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