Turning off the Graphical Desktop
Linux distributions can start and stop the graphical desktop in various ways. For Debian-based systems, the Desktop Manager runs as a service which can be simply stopped. For RPM-based systems, the Desktop Manager is run directly by init when set to run level 5; switching to a different run level stops the desktop.
Use the sudo service gdm stop or sudo service lightdm stop commands, to stop the graphical user interface in Debian-based systems. On RPM-based systems typing sudo telinit 3 may have the same effect of killing the GUI.
