If you want to escape the GUI in Linux, press ctrl-alt-F1 to get a tty style terminal session. There are at least six tty style sessions using the other function keys up to ctrl-alt-F6. Ctrl-alt-F8 will bring back the GUI. In Red Hat, it seems like it preserves the GUI, but under Ubuntu, your current GUI session is lost. Escaping the GUI is handy if it hangs or the mouse isn’t working. From the tty session, the machine can be repaired or rebooted cleanly.