Welcome to LinuxQuestions.org. The real command to close X is ctrl + alt + backspace
Remember though that, if you use a graphical login, it will not kill X completely, you will simply get back at the login screen. To change your login from graphical to text mode, edit (as root) the following line located at /etc/inittab
Next time you reboot, you will have a text mode interface. After login, use:
To start the X manager. One more thing, pressing simultaneously:
ctrl + alt +F[F keys from 1 - 6] will also bring a terminal for you when in graphical mode. Pressing ctrl + alt + F7 will bring you back to the X.