How to run Ubuntu without GUI in Virtual Box?
Solution 1:
The easiest way is to install Ubuntu Server inside VirtualBox, it cames with no GUI by default, just command line.
If you change your mind and need a GUI, try Lubuntu,it uses LXDE a quite light GUI.
Solution 2:
If you have installed ubuntu on vbox than run ubuntu and press right-ctrl + F2
By doing this you will enter terminal mode and to come back anytime to GUI PRESS right-ctrl + F7
By doing this i think you dont even need to install new ubuntu you can run your current ubuntu without graphics and can practice
Hope this will help you
Solution 3:
You can try installing Xubuntu.