In Ubuntu you may wish to stop or start the Gnome desktop and still access TTY’s. For example if you are running the box as a web server then while you may like the ease of use offered by the GUI you don’t want to incur the overhead of the GUI when running Apache/MySQL. So after doing all the mods you leave Apache running but turn the Gnome Desktop off.
To access a TTY hit ctrl-alt-F3
Or any of the other 4 (in total) TTY’s hit ctrl-alt-F3 to F6
To turn off the GUI
sudo service gdm stop
That’s it. The GUI is dead
To restart it
sudo service gdm start
In the old days (aka Ubuntu 16.04 and before) ctrl-alt-F1 through to F6 opened TTY’s. Now though in 22.04 (unsure about 20.04) it’s ctrl-alt-F3 to F6. But whatever the level of Ubuntu you are running Gnome Desktop stop start commands are the same.
Ctrl-alt-F2 takes you back to the GUI (if it’s running)
Ctrl-alt-F1 takes you back to the GUI log in screen (if the GUI is running)
You don’t have to stop or start the Gnome desktop to access any of these TTY’s. They are always there and always available. If you have accessed one and you want to return to the Gnome Desktop simply its just ctrl-alt-F2
If you want to go to the Gnome Desktop login screen and (say) login as another user it’s ctrl-alt-F1.
You can actually turn off the Gnome Desktop from a TTY you have opened within the Desktop itself (aka ctrl-alt-t or right-click and select open terminal). Then, while the Desktop will die, you will be left with a blank screen not at a TTY. If you do this you can get to a TTY by using ctrl-alt-F3 through to ctrl-alt-F6
If you do ctrl-alt-F1 or ctrl-alt-F2 and the desktop is not running you will just get a blank screen. Use ctrl-alt-F3 through to ctrl-alt-F6 to recover.