|
Welcome to T.he L.inux G.uide O.nline
The following is a reference to Linux. Please feel free to
contact me for any details.
Chapter 05 - The X-Window System
5.1 Introduction
The X Windowing system is such a vast and deep subject that
any introduction to it will be very restricted even if details
were to be touched upon. The history, the technology and the
economics behind one of the most successful and customizable
Windowing systems if fascinating to say the least. Here we
will look at a little of all these topics so that you will
have a feel of what you are dealing with, when using the X
Windowing system on your Red Hat system.
Windows and Mac users must be used to seeing the same interface
every time the computer boots, but for probably minor variations.
This must be getting boring after some time. Linux and Unix
users will definitely not feel the same. The X Window system,
the Graphical User Interface (GUI) for Linux and Unix is an
extremely powerful and flexible system. X Windows allows you
to choose any graphical interface you would like to use. You
can get one like the interface of Windows or Mac or you could
get one totally and radically different.
The X Windowing system, or X for short, was developed at
the Massachusetts Institute of Technology. It was developed
n 1984 with the help of DEC (now a part of Compaq) and IBM.
The objective was to develop an operating environment that
could be run on any hardware platform. X is based on the Client-Server
architecture and can run across the network, which means that
it could run a host server located in Timbuktu and interact
with your computer in Chennai. The X system is made of two
components - the X server and the Client (the window managers).
These components are completely independent of each other.
Thus what you see can be totally left to the window manager
and the backend performed by the server. This obviously means
that any body can write a window manager and completely overhaul
the look and feel of the interface. Also a number of combinations
are possible between the two and the user can different results
of feel and performance.
A free port of the MIT X system is now available for Linux
under the name of XFree86. The version 11 release 6 (X11R6)
for 80386, 80486 and Pentium machines was developed by a team
of programmers originally headed by David Wexelblat. This
release provides all the binaries, support files, libraries
and tools for the required installation. The window manager
you will use however depend on your choice. These will be
investigated in detail in the next chapter.
Please note that to do most of the configurations detailed
in this chapter will require the administrator privileges.
Be sure to log in as root to be able to change the configuration
files.
5.2 Setup and Configuring Xfree86
If you installed Red Hat Linux as discussed before and also
completed the configuration of X to your satisfaction then
this chapter is probably not for you. You will still gain
by knowing how to change the configuration files etc. Here
we will look at installing the X from scratch. Right from
the installation of the required binaries to its configuration.
Installation of the X server is by installing the XFree86
rpms. Mount your CD-ROM and change to the rpms directory,
which will typically be the following and install the rpm
files.
$ mount /mnt/cdrom
$ cd /mnt/cdrom/RedHat/Rpms/
$ rpm -ivh XFree*.rpm
This will install the XFree86 software. You will find a series
of directories as shown under the /usr/X11R6 tree
/usr/X11R6/bin - where most of the X11 clients are stored
/usr/X11R6/include - programming header files and directories
of bitmaps and pixmaps.
/usr/X11R6/lib - X11 software libraries
/usr/X11R6/man - manual pages
Depending on the software installed this can take anywhere
between 40 and 400 MB, and even more if you installed lots
of X window managers.
The largest hurdle that many users face is coming up with
a working version of the XF86Config file. If you already have
a system working, chances are that your earlier file will
work. But we will now try to get a new system to start working.
The first thing that you have to do is red as much of documentation
as possible. Just about all that you will need is under the
/usr/X11R6/lib/X11/doc directory. Read also a XFree86-HOWTO
under the /usr/doc/HOWTO directory. Also read the man pages
for X and XFree86.
You also need some information about your hardware. Preferably
get information about the video card, mouse and the keyboard
before you begin. You can use one of the two tools available
for the configuration. The xf86config is a text based wizard
interface. The Xconfigurator has the advantage of providing
a graphical interface (thereby sensitive to unknown cards)
and also provide a lot of flexibility in choosing color depths
and screen resolutions. (If you do not have these packages
installed you may install them from the CD-ROM. They will
have similarly named rpm files. Also install any dependant
packages. The xf86config requires the VGA drivers to be present)
You are lucky if your hardware exactly matches the configuration
provided by these programs. Problems can arise if you entered
incorrect information or the chipset is not supported. You
may rerun the configuration utility as many times till you
are satisfied with the output. If your chipset is not supported
you may have to buy one of the commercial X distributions
from various vendors.
5.3 Xconfigurator
Red Hat's Xconfigurator produces an XF86Config file after
it probes your system and gets information from you. Run the
utility from command line
$ Xconfigurator
After selecting OK from the first screen you will be presented
with the second screen where the program will probe for the
video card and presents the results. If your card is listed,
well and good. Otherwise you may have to get additional information
and help for your card.
You will now be presented with a selection of monitors. If
the program detects your monitor, you are luck and can expect
exceptional performance from the X system. Otherwise scroll
down and choose you monitor (or its nearest substitute, though
a safer alternative will be to choose the custom monitor and
configure it manually) from the list of about 200 monitors.
If your monitor is not listed, choose the "custom" monitor.
You will then be presented an introductory dialog and then
a list of monitor resolutions and frequencies. Check your
monitor manual and choose the closest alternative. If the
values do not exactly correspond to that of your monitor choose
the closest ones and then change the values manually in the
configuration file.
The next dialog asks you choose your vertical frequency range.
Again select the closest one, which you can change later to
suit your monitor exactly.
The next dialog asks you if you want to probe the monitor
for resolution and color depth. Although the safest route
is not to probe, those having an unlisted monitor will benefit
because the program will automatically get some of the information
it needs.
Select the amount of video RAM you have on the system. Interestingly
no matter what you choose, the value will be inserted but
will be left out commented. You will have to then enable it
with hand. Also if you have memory more that the options listed
you will have change it by hand.
Xconfigurator next asks you for the clockchip in your video
system. If you are not sure whether your video card uses clockchip
settings, select "No clockchip". If you are sure of the chip
then choose one from those listed.
The next dialog lists the various video resolutions at different
color depths. Select those that can be supported by your monitor.
When you are finished, click the OK button.
Xconfigurator next saves your configuration file and exits.
Run startx and check if the configuration is correct. If
your server runs but does not support high resolutions you
may want to change the resolutions, probably sacrificing color
depth for higher resolution.
5.4 XF86Config and .xinitrc
The configuration obtained earlier is stored in the file
/etc/X11/XF86Config. This file is the entire source of information
about your video subsystem. Just like any other configuration
file, this too has the form that allows it to be both human
readable and machine compatible. The file has several sections
that define various values that the server should use while
starting up. Be sure to have created at least a skeleton file
as shown earlier before you go ahead and explore.
XF86Config Files Section
This section tells the X server where to get the color name
database and the system database. There is normally no need
to change the defaults.
XF86Config ServerFlags Section
These can be used to configure special actions allowed by
your server. Enable a particular option by removing the "#"
sign before it. (# implies a comment and will be ignored.
Removing it will therefore cause the line to be read and processed
next time the server starts.)
XF86Config Keyboard Section
This section tells the X server what kind of keyboard to expect,
and other settings such as language type, key character layout,
and manufacturer.
XF86Config Pointer Section
This tell the server what pointer, mouse to use and how the
buttons are handled. The section varies for PS/2, bus and
serial (auto) mice. Note that the device /dev/mouse is a symbolic
link to the actual mouse device on the system. (such as say
/dev/ttys0 for the serial mouse on COM1). Two-button mouse
users will definitely want to enable the three-button emulator
(clicking both the buttons at once acts like a third button
click).
XF86Config Monitor Section
The first several parts are easy to understand. But if you
have not been able to configure your video system here is
the place you can learn about things that will allow you to
try and get the configuration right. The monitor section contains
specific details about your monitor, such as the name, horizontal
and vertical sync ranges. In addition there are also a number
of critical modelines that are what you need to change to
fine-tune your X server. For more details see the files VideoModes.doc
and README.Config under the /usr/X11R6/lib/X11/doc directory.
Another good tutorial is the XFree86-Video-Timings-HOWTO under
the HOWTOs directory.
The basic parts of a modeline are ten different values representing
(from left to right)
- A label of the screen resolution
- A video frequency in mHz
- The number of visible dots per line of your display
- The Start Horizontal Retrace value (number of pulses before
video sync pulse starts)
- The End Horizontal Retrace value (end of the sync pulse)
- The total number of visible and invisible display dots
on your display
- The Vertical Display End value (number of visible lines
of dots on your display)
- The Start Vertical Retrace value (number of line before
the sync pulse starts)
- The End Vertical Retrace value (number of lines at the
end of the sync pulse)
- The Vertical Total value (total number of visible and
invisible lines on your display)
XF86Config Device Section
The device section contains details about your video chipset
such as RAM or clockchips. You need to uncomment the line
containing the VideoRam setting for it to be actually visible.
This section of the configuration is critical, as it tells
the server what exactly to expect from the video chipset.
XF86Config Screen Section
This section tells the X server what color depth and screen
size to use (the bit depth and the resolution). This section
contains for your chosen server (SVGA or VGA or MONO or any
of the accelerated servers like the S3 or the Mach of the
AGX etc) what resolutions and virtual screen sizes to support.
In a particular session you can toggle resolutions using the
Ctrl+Alt keys and the (+) or the (-) keys. The color depth
can be chosen at the time of starting the X server as shown
below.
$ startx -- -bpp 16
Starts a session in the 16-bit color mode.
The .xinitrc file
When the X server is started, details about which window
manager to use and the other X clients to start can be found
in a file called the .xinitrc in your home directory. A template
file named xinitrc can be found /etc/X11/xinit directory which
can be copied to your home directory (as a '.' file) and modified
to suit your needs.
Although the file contains shell scripts logic to load in
the system resources or to set environment variables, it is
possible to write a file by hand that can be used instead.
The X Resource files
Most of the default settings for the various X clients are
stored under the directory /usr/X11R6/lib/X11/app-defaults.
These are text files that have a lot of configurable options,
that can be changed. Any changes here affect the users on
the whole system. You may also create a .Xresources file in
your home directory and put the appropriate new values of
the variable there for the different X clients. The format
is described in detail in the X man page.
Booting by default into the GUI
This is achieved under Red Hat Linux by changing the following
line in the /etc/inittab file
id:3:initdefault
to
id:5:initdefault
And be careful not to change any of the other entries while
you are at this.
5.5 Troubleshooting
One of the best sources for information for troubleshooting
can be found at the site www.xfree86.org. The FAQ there covers
a lot of the problems faced by the users during installing
and configuring the X server.
|
