What Is the X Window System
The last line of the file should run the window manager; in fact, that
can be the only entry in the file. But it's useful if you want to do
work, to set up at least a couple of xterm windows and maybe start a
browser or any other application program that you use regularly. Here,
for example, is my .xinitrc file:
#!/bin/bash
xterm -sb -geometry 80x55+5+5 &
xterm -sb -geometry 80x55+530+30 &
oclock -geometry +1450+920 -bg ivory -fg blue &
xscreensaver &
exec fvwm
This file starts up two xterm windows, with sidebars and the specified
geometry. 80x55 is the size of the window (80 characters wide and 55
lines long), and +5+5 indicates where on the screen the upper-left
corner should be placed. Every line except the last one ends with an &
to put them in the background so the next line can be executed. After
starting up a clock with an ivory background (the face) and a blue
foreground (the hands), and the xscreensaver program, the script
runs the window manager, fvwm.
Now we are ready to establish that we don't want to boot into X. As
root, edit the file /etc/inittab and update the line that sets up the
initial runlevel. We want it to start in runlevel 3 (multiuser mode)
instead of runlevel 5 (X11 mode). Specifically, change the line
id:5:initdefault:
to read
id:3:initdefault:
Then when you restart the system, it will boot to a regular terminal
window instead of to X11, displaying a login prompt. After you log
in, you can start X:
$ startx
As long as the startup script is running, the X server will also
continue running. Since the last command in the script starts the
window manager, X will continue to execute until the window manager is
terminated, which terminates the script. Thus in effect, stopping
execution of the window manager also stops the X server.
In fvwm, to stop the window manager, select Exit Fvwm from the root
menu--the menu you get when you click on
the root window (the background behind the other windows). Figure 1
shows an example of an fvwm root menu:
Figure 1. An fvwm root menu
Exit Fvwm is the last entry. When you click on it, a submenu asks whether you really want to quit fvwm, whether you want to restart fvwm,
or whether you want to start a different window manager.
Figure 2 shows my screen running fvwm, based on the .xinitrc file we
just saw, after I'd been working for a while, running commands
in the xterm windows and starting some additional X clients.
Figure 2. Using fvwm to run commands and start X clients
The X Server
The X server manages the display hardware. The server captures input
events from the user via keyboard or mouse (or other input device)
and passes the information to a client application that has requested
it. It also receives requests from the application to perform some
graphical action. For example, if you use your mouse to move a window
on the screen, the X server passes the information to the window
manager, which responds by telling the server where to reposition the
window, and the X server performs the action. If the client is a
calculator, such as xcalc, it might request that digits be displayed into
the window as the user clicks on buttons to enter a number.
In any case, it is always the server that interacts with the hardware.
Thus only the server software has to be hardware-specific. In
fact, only the parts of the server that actually interact with the
hardware need to be rewritten for X to be ported to new systems or to
be usable with a new terminal or a new type of input
device, for example. As long as the X clients are written to use the X Protocol,
they can run on any system and communicate with the X server.
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