When you start working on Ubuntu VM [running on MacOS in VirtualBox], you will discover that the CMD (⌘) key does not work the same way it did on your Macbook. On MacOS you must do CMD+C to copy something. On Ubuntu you must instead do CTRL+C to copy something. Definitely not what you want! If you press CMD+C when inside the Ubuntu VM, you will instead break out of VirtualBox’s Full Screen mode. There is a simple fix to this problem!