Here is some notes about using Ubuntu guest on Mac host in VirtualBox.
Super Key
The super key does not work in Ubuntu when running on Mac host in VirtualBox. I from a workaround from here and here, which is:
“sudo apt-get install compizconfig-settings-manager”
Open the utility and go to “Ubunti Unity Plugin -> Launcher -> Key to show the Dash, Launcher and Help Overlay”
Change it from “<Super>” to “<Control><Alt>”
This change will make “<control><Alt>” keys combination can be used to open Dash and etc but it cannot replace all the functionalities of the super key.