Running Linux, 5th Edition - Matthias Kalle Dalheimer [325]
HorizSync 31.5, 35.2, 37.9, 35.5, 48.95
Your monitor manual should list these values in the technical specifications section. If you do not have this information, you should contact either the manufacturer or the vendor of your monitor to obtain it. There are other sources of information, as well; they are listed later.
You should be careful with these settings. Although the settings VertRefresh and HorizSync (described next) help to make sure that your monitor will not be destroyed by wrong settings, you won't be very happy with your X setup if you get these values wrong. Unsteady pictures, flickering, or just plain snow can result.
VertRefresh specifies the valid vertical refresh rates (or vertical synchronization frequencies) for your monitor in Hz. Like HorizSync, this can be a range or a list of discrete values; your monitor manual should list them.
HorizSync and VertRefresh are used only to double-check that the monitor resolutions you specify are in valid ranges. This reduces the chance that you will damage your monitor by attempting to drive it at a frequency for which it wasn't designed.
You can use the ModeLine and Mode directive to specify resolution modes for your monitor. However, unlike earlier versions of X.org, this is not strictly necessary any longer; the Monitor section shown earlier (which comes from a laptop) doesn't have one. Instead, this information is moved into the following section, Modes.
The Modes section, of which there should be one for every monitor you have configured, lists the various video modes that the X server should support. An example:
Section "Modes"
Identifier "Modes[0]"
Modeline "800x600" 36.88 800 832 912 1024 600 601 604 621
Modeline "800x600" 40.00 800 840 968 1056 600 601 605 628 +HSync +VSync
Modeline "1400x1050" 109.01 1400 1480 1632 1864 1050 1051 1054 1083
Modeline "1280x1024" 98.60 1280 1352 1488 1696 1024 1025 1028 1057
Modeline "1280x960" 97.68 1280 1352 1488 1696 960 961 964 993
Modeline "1152x864" 78.82 1152 1216 1336 1520 864 865 868 894
Modeline "1024x768" 61.89 1024 1080 1184 1344 768 769 772 794
Modeline "800x600" 36.88 800 832 912 1024 600 601 604 621
Modeline "800x600" 40.00 800 840 968 1056 600 601 605 628 +HSync +VSync
Modeline "640x480" 23.06 640 656 720 800 480 481 484 497
Modeline "1400x1050" 109.01 1400 1480 1632 1864 1050 1051 1054 1083
EndSection
The Identifier line refers to a name specified in the Monitor section. The following Modeline lines each specify a video mode. The format of Modeline is:
Modeline name dot-clock horiz-values vert-values
name is an arbitrary string, which you will use to refer to the resolution mode later in the file. dot-clock is the driving clock frequency or dot clock associated with the resolution mode. A dot clock is usually specified in MHz and is the rate at which the video card must send pixels to the monitor at this resolution. horiz-values and vert-values are four numbers each; they specify when the electron gun of the monitor should fire and when the horizontal and vertical sync pulses fire during a sweep across the screen.
How can you determine the Modeline values for your monitor? That's difficult, especially since a lot of the documentation files that used to be shipped with X.org are no longer included, probably because they became outdated and haven't been updated yet. Your best bet is probably to use one of the configuration file generators mentioned in the previous section to get a set of start values and then tweaking these until you reach a satisfactory setting. For example, if while running X the image on the monitor shifts slightly or seems to flicker, tweak the values little by little to try to fix the image. Exactly what you need to adjust is difficult to say because it depends a lot on your actual graphics hardware, but with some experimenting, you usually get good results. Also, be sure to check the knobs and controls on the monitor itself! In many