raspberry pi openbox screen resolution

Sometimes a monitor won't report it's largest available screen resolution correctly. In such a case, you'll have to set it manually. My first hit on Google suggested some xrandr trickery which didn't work for me. Here's what did.

sudo raspi-config

Go to Advanced Options -> Resolution and choose yours. Both DMT and CEA modes worked on multiple devices, just make sure you got the right screen ratio and refresh rate.