Most people use SSH and console to access linux machines - physical or virtual boxes! Thus for you guys who use virtualbox might find it really cumbersome to have to fire off a GUI to access the machine, even if you decide to minimise the window and SSH directly from the client. Luckily there is a solution to run a VirtualBox machine in the background.
You can use VBoxManage to start the machine in the background by running the following command:
VBoxManage startvm my_machine --type headless
Just remember to setup an SSH server on the virtualbox so that you will be able to access it remotely!