I'm trying to get a functional Ubuntu instance running in VirtualBox on my iMac 27". The iMac has a resolution of 2560x1440, and I'd like to run Ubuntu in full screen at that resolution.
I've installed the Guest Additions that come with VirtualBox (rather than the ones in the archive). I'm using Ubuntu 11.10 64 bit.
The display currently runs at 1600x1200, and when I run the displays dialog (or xrandr), I get a list of resolutions that are 1600x1200 or smaller, and are all at 4:3 aspect ratio (whereas the iMac monitor is 16:9).
The settings for the virtual machine have video memory set to 128MB. Whether I run the VM with or without 3D acceleration makes no difference to the available resolutions (although with 3D acceleration enabled, launched windows aren't visible – a different question perhaps).
I have a natty VirtualBox VM that does run at 2560x1440, so I know it's possible. However, I don't know how to achieve it.