I am at the gnome 2 login screen but I want to exit and re-enter command-line environment. I remember there was a combination hot key one has to invoke.
Press ctrl+alt+F1 to switch to a virtual console.
Login using your normal login and password.
Press ctrl+alt+F7 to return to your GUI at any time.
If you are doing something like installing NVIDA drivers, you may actually need to kill the login screen. In Ubuntu this is
lightdm, though this may vary per distro.
# Stop login window service sudo service lightdm stop # Start it back up again sudo service lightdm start
Note: I would have tried to summarize in a comment, but didn't have enough points.