HuaMin wrote:what to press to get into recover mode?
Recover mode for what? Please explain more.
Virtualbox has the Host key, displayed in the VM's standard window on the lower right, usually the right Ctrl key. A tap of this key will release the keyboard and mouse from the VM so the host OS can receive keys and mouse clicks.
If this 'Recover mode' is an Ubuntu thing, then web-search Ubuntu's help channels for how to do it on a real PC, then do the same to the VM.