The default X installation provides a graphical login after you have installed X and rebooted. This graphical login screen is actually an X program known as gdm, or the GNOME Display Manager.
In addition to prompting for username and password, gdm implements authentication using the X standard, host-based access control, and other security-conscious facilities.
If you change your default run-level, gdm might not start automatically. Run-levels describe Linux boot states and include graphical, multi-user, and standalone modes of operation.
The run-level a Linux system boots to is specified in /etc/inittab, and is rarely modified once set.
When to use startx
If you are not in the graphical run-level and you want to start the X server, then you may use the startx script. This script is simply a front-end for xinit, which actually starts the X server and any user-configured clients.
The xinit program checks to make certain no X server is already running, sets up lock files and other server-related details, then executes the X server proper.
To start the X server, you type startx at the command prompt.
As the X server starts, notice the information it returns about your hardware. This screen shows several error messages you may use for troubleshooting.
You can now use the X Windows System. This screen shows the application window that appears in the lower right corner when using fvwm2 a common window manager.
Do not call xinit directly. The startx script performs setup activities that, if not performed, would make using your X session practically useless for productive purposes. X will not be initiated with the proper options. startx takes care of all of this.
Sometimes you might want to pass options directly to the X server to change its behavior from the default. The startx script sends all its command line arguments after a -- to the X server.
startx -- -bpp 8
will instruct the X server to use 8-bit color instead of its configured default.
The next lesson discusses configuring the X server startup with .xinitrc.