Refer to my title, is it possible to do that? Let say im on Unity with running VPS on Virtual Box, but i want to switch to Gnome without shutdown my VPS and run back on Gnome. Is it possible?
You can open n sessions with the same user :
you could install Xephyr o Xnest(older) and then open a new Xsession in a window (like a Picture In Picture):
or CTRL-ALT-F1, login and open a new X-window session:
And move between sessions with CTRL-ALT-F7,F8 Just beware of RAM :)
It is not possible to switch the environment out from underneath running applications, as your current user. You can however log in to an additional session as a different user, with the "switch user" feature from the locked screen unlock display, or the session indicator (gear icon in the upper right under Unity).