Running Into Trouble (Running Linux)

10.7. Running Into Trouble

Often, something will not be quite right when you initially fire up the X server. This is almost always caused by a problem in your XF86Config file. Usually, the monitor timing values are off or the video-card dot clocks are set incorrectly. If your display seems to roll, or the edges are fuzzy, this is a clear indication that the monitor timing values or dot clocks are wrong. Also be sure you are correctly specifying your video card chipset, as well as other options for the Device section of XF86Config. Be absolutely certain that you are using the right X server and that /usr/X11R6/bin/X is a symbolic link to this server.

If all else fails, try to start X "bare"; that is, use a command such as:

X > /tmp/x.out 2>&1

You can then kill the X server (using the Ctrl-Alt-Backspace key combination) and examine the contents of /tmp/x.out. The X server reports any warnings or errors--for example, if your video card doesn't have a dot clock corresponding to a mode supported by your monitor. This output can be very helpful in diagnosing all kinds of problems. Examine it closely if your X server does not start up at all, does not provide the resolutions you wanted, or shows a flaky, snowy, or otherwise insufficient picture. Even if everything works to your satisfaction, you might want to check this file for interesting information that the X server has found out about your hardware. The lines starting with (**) contain data that you provided yourself in the configuration file, while lines starting with (- -) contain data that the X server has found out itself.

The file VideoModes.doc included in the XFree86 distribution contains many hints for tweaking the values in your XF86Config file.

Remember that you can use Ctrl-Alt with the plus or minus on the numeric keypad to switch between the video modes listed on the Modes line of the Screen section of XF86Config. If the highest-resolution mode doesn't look right, try switching to lower resolutions. This lets you know, at least, that the configurations for those lower resolutions in your X configuration are working correctly.

Also, check the vertical and horizontal size/hold knobs on your monitor. In many cases it is necessary to adjust these when starting up X. For example, if the display seems to be shifted slightly to one side, you can usually correct this using the monitor controls.

The Usenet newsgroup comp.windows.x.i386unix is devoted to discussions about XFree86. It might be a good idea to watch that newsgroup for postings relating to your video configuration; you might run across someone with the same problems as your own. If this fails, please contact your Linux distributor; their support staff should be able to help you as well.