When the X Window System exits to the command line, the frame buffer's DDX module must send an ioctl to the frame buffer driver. This ioctl triggers the frame buffer driver to call the terminal emulator's mode change callback function. This communication keeps the frame buffer driver and the terminal emulator in agreement about the video mode if the X Window System starts and then changes the video resolution before exiting. The frame buffer driver and the terminal emulator must agree about the video mode at all times. When the frame buffer driver and the terminal emulator do not agree about the video mode, the information on the screen is illegible and meaningless.