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Title: Configuring the X server

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Configuring the X server

Symptom:

• The picture displayed on the monitor flickers.

• The picture is shifted (left/right, up/down).

• The picture is too big or too small and doesn't fit the screen

• No picture appears.

Cause:

There are a lot of possible reasons for this. One of them will be explained here :

The graphics device is accessed by the X server with a modeline, that causes a signal, that cannot be displayed correctly by the monitor.

Solution:

• Creating modelines manually is a hard job. Older X server distributions (up to and including XFree-3.1.2B) contained the file /usr/X11R6/lib/X11/etc/Videomodes.doc which explained the procedure in detail. However in newer distributions this file isn't contained anymore since it isn't needed nowadays. The reason for this is the following :

• There is a programme named xvidtune. You can use it to configure a mode line interactively. Start xvidtune in an xterm. If there should be errors, please see xvidtune

• Often a much easier solution helps: most of the time there are several modelines for the same resolution in the file /etc/XF86Config, produced by xf86config. Comment out all lines for the same resolution except for one. Take a look at the effect. If you like it, take this mode line, if not, repeat the process with the other modelines. It could be that the X server cannot find any fitting dot clock for the given modeline. It will inform you about this in the file ~/.X.err:

  Mode "0000x0000" deleted. (where 0000x0000 is the modes name).

• Another solution is to copy already existing modelines for your graphic card and your monitor from the file /usr/X11R6/lib/X11/doc/Monitors.

• You will find useful information about the configuration of X and the building of the XF86Config file in the files in the directory /usr/X11R6/lib/X11/doc.

Important hint:

Never enter higher values for the horizontal and vertical frequency in /etc/XF86Config than your monitor can handle. Wrong or too high values can cause severe damage at the monitor.

Please read carefully the technical specification of your monitor. If you are unsure about the settings you should try somewhat smaller values. And again : Be careful ! .

See also:

Installing XFree with XF86Setup - what do I need?
XFree with xf86config - what do I need?
Adjusting the screen under X11
Configuring the screen resolution
P9000 server and virtual resolution

Keywords: X SERVER, SCREEN, MONITOR, XVIDTUNE

Categories: X Server

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