A sample XFree86Config file
That's one big file alright !
On a Red Hat distro, this file
lives in /etc/X11/ . Before editing, you should save the original file
to eg. XF86Config.orig. It looks pretty big, but when you remove all the
comments, it looks more reasonable. Besides, most of the stuff can be left
as is, and you'll only have to play with three sections: Your video setup
([Screen] section) is composed of two sections : [Device], which is the
video adapter, and [Monitor], which is, er; the monitor. In other words,
Screen = Device + Monitor.
Important data to collect beforehand
The first thing to do, is to
check the features of your video adapter and your monitor in the manual
or on the manufacturer's web site. As far as the video adapter is concerned,
you'll want to know the name of the manufacturer, the chipset used on your
particular adapter, the amount of on-board RAM. To avoid customizing their
PCB (the board itself), manufacturers typically do not print the name under
which their video adapter is sold, so you should read what it says on the
chipset to known what kind of adapter you have (eg. ATI/Rage Pro, S3, Matrox/MGA,
As for the monitor, check
what maximum refresh rates it supports for vertical (in Hz) and horizontal
(KHz). An average upper limit for vertical refresh rate on a 17" monitor
is about 100Hz for higher end products, while an average maximum horizontal
rate would be about 100KHz.
Documentation on X often warns
you that you could fry your monitor if you set a maximum rate that is higher
than your monitor actually supports, but today's monitors are typically
multi-sync, are built to withstand this kind of error for a short period
of time, and as long as you don't try rates that are obviously unreasonable
for your particular monitor, it's safe to go by trial and error for
a few minutes until you get it right. At least my 3-year old 17" Targa
monitor didn't blow up during the past two years I spent learning about
Anatomy of the beast
Below is the XFree86Config file
I use on that older 17" monitor and a PCI Matrox adapter with 4Meg of on-board
RAM. You'll get much better video with cutting edge monitors like Iiyama
or Sony, and AGP adapters.
# 1024x768 @ 70 Hz,
56.5 kHz hsync
75 1024 1048 1184 1328 768 771
777 806 -hsync -vsync
"My Video Card"
ViewPort 0 0
I showed the important parameters
in bold letters.
In the "Monitor" section, the
maximum rate of the HorizSync and VertRefresh must match what your monitor
actually supports. To avoid hurting your eyes when spending all that time
in front of your computer, you must set vertical refresh rate to above
70Hz. A quick and easy test to see if it is set high enough, is to start
in graphic mode (If you didn't get X running yet, try with the Other OS),
open a window with a lot of white in it (eg. NotePad in Windows), and look
about 10 inches/25 cm above the monitor. You can tell if the picture is
stable (good) or flickering (not good). If the latter, you're killing your
The second important parameter
in this section is the Modeline. Once you have X running with the right
definition (eg. 1024x768), you can run character-mode application xvidtune
to tune up this setting, but to get X started, the numerous Modeline lines
in the original file should be good enough. Check the comments above each
line, and see whether any matches the horizontal and vertical refresh rates
you indicated in this section. In the file above, I only kept the Modeline
that matched my monitor : I told X that its top horizontal refresh rate
was 58KHz and its top vertical refresh rate was 85Hz, so the only Modeline
that matched is this one (56.6Khz as horizontal rate, and 70Hz as vertical
Most likely, you'll find more
fine-tuned Modeline settings on the web once you got X running. Check www.xfree86.org
The only important setting here
is the amount of on-board RAM. The more RAM, the more colors and the higher
This is where the monitor and
device sections are turned into your actual video setting. Driver
match the X server that is installed in your host, eg. XFree86_SVGA in
this case. On a Red Hat distribution, this program lives in /usr/bin/,
and there's a symlink in /etc/X11/ which is X.
Device and Monitor
must match the Identifier setting in the Device
and Monitor sections
so X can find them.
Depth is the number
of colors you want to use (16 is 16-bit color; 8 is 8-bit color, ie. up
to 256 colors.)
Modes is the screen
definition you want to use. If there are several Modelines in your Monitor
section, you can have several Modes
setting, eg. Modes "1152x864" "1024x768" "800x600",
which lets you switch definition by using the CTRL-ALT-+ key combination.
Fine tuning X
Once you have X running, open
a terminal window and run xvidtune to finish setting up the Modeline parameter.
xvidtune will let you change the left/righ/up/down setting along with making
the picture narrower/wider/smaller/taller. Once you're satisfied with the
result, click on Fetch, and xvidtune will paste the current setting in
the terminal window, which you can then copy/paste with the mouse into
your XFree86Config file.
The picture is curved on the
That's because you set the maximum
horizontal rate too high. Choose a smaller value.