Likely the easiest way to accomplish this is by simply isolating the multi-user target, as right now your Tensorbook is running in the graphical target.
To do this, run:
systemctl isolate multi-user.target
This will require you to use your login credentials again and you’ll be limited to a TTY. If you find this works for you, to make the multi-user target the default target for when your machine boots, run:
systemctl set-default multi-user.target
Another option would be to completely reinstall Ubuntu Server, as opposed to Ubuntu Desktop. If you’d like to try this, here is our guide on how to do so. There is a link to another guide on how to install Ubuntu installation media, just be sure to choose the Ubuntu Server ISO.
Hopefully this helps and please do let us know should you have any further questions or concerns!
Linux Support Engineer