You just installed a brand new copy of the OS on your brand new system, removed the system DVD and tried to boot for the first time. The system appeared to boot up OK (you saw GRUB loading) and a couple of systems started up (like udev), then the screen went blank and your display said (in broken Engrish, "VGA Mode Not Support"). What do you do?
Lucky you. XOrg has used the EDID values from your display (or the lack of EDID values, if you have a really old display) to pick a set of display parameters that your display doesn't support. You now have to repair this infelicity using a standalone rescue disk (isn't it great that you just installed a brand new, fresh copy of the OS and you're already resorting to booting from a rescue disk and hacking obscure display manager parameters -- no wonder Linux is such a hit with Joe User).
Our favorite standalone rescue disk is Knoppix (hint to XOrg programmers: if Klaus Knopper can figure out the proper display parameters for the display, maybe you could too, if you just tried a bit harder). So, begin by getting yourself a copy of KNOPPIX (the CD works perfectly fine):
http://knopper.net/knoppix/index-en.html
And burn the ISO image onto a CD (or DVD, if you took that route).
Then, boot up the CD/DVD in the new machine and mount its root file system. Look around in the /media directory for the subdirectory that matches the partition where the root file system resides (Knoppix thoughtfully creates subdirectories in /media for all of the disk partitions that it finds at startup). In order to mount things, you will need to issue the "su" command in a shell window first. You'll need to do something like this:
su
mount /dev/sda3 /media/sda3
To edit the XOrg config file, locate the file (usually in /etc/X11/xorg.conf) and invoke the Kate editor (there's no EMACS, sorry) on it:
cd /dev/sda3
kate etc/X11/xorg.conf &
This will let you get at the offending display section of the file. A quick fix is to force the display resolution to one of the well-known VESA resolutions by putting the "Modes" line in the Display SubSection. You might also have some success with setting the HorizSync and VertRefresh parameters in the Monitor Section to the correct range for your monitor (although it does appear possible to use values that fall strictly within this range and still offend the monitor's sensibilities). Also, if EDID is not used to get the monitor's parameters, this could be the problem. Here's the basic idea:
/etc/X11/xorg.conf:
.
Section "Monitor"
Identifier "Monitor0"
ModelName "My LCD Panel 1024x768"
HorizSync 31.5 - 48.0
VertRefresh 56.0 - 65.0
Option "dpms"
EndSection
.
.
.
Section "Screen"
Identifier "Screen0"
Device "Videocard0"
Monitor "Monitor0"
DefaultDepth 24
SubSection "Display"
Viewport 0 0
Depth 24
Modes "800x600" "640x480"
EndSubSection
EndSection
If worst comes to worst, you may have to define your own ModeLine information and then use it in the Display subsection. To do this, you must figure out one or more modelines that can be used to set the various screen resolutions supported by your display. There should be a chart in the back of your display's manual that lists all of the supported modes (beware that some of the charts we've seen have the vertical and horizontal frequencies exchanged - a good clue is that the vertical frequency is usually the one that matches the number in the VESA name). First off, you should try to pick one of the standard modes from the list below. Also, it is best to try and pick the highest vertical refresh rate (in Hz) supported by your display:
# 640x400 @ 85Hz (VGA VESA 85) hsync: 37.9kHz
ModeLine "640x400" 31.5 640 672 736 832 400 401 404 445 \
-hsync +vsync
# 640x480 @ 60Hz (Industry standard) hsync: 31.5kHz
ModeLine "640x480" 25.2 640 656 752 800 480 490 492 525 \
-hsync -vsync
# 640x480 @ 72Hz (VGA VESA 72) hsync: 37.9kHz
ModeLine "640x480" 31.5 640 664 704 832 480 489 491 520 \
-hsync -vsync
# 640x480 @ 75Hz (VGA VESA 75) hsync: 37.5kHz
ModeLine "640x480" 31.5 640 656 720 840 480 481 484 500 \
-hsync -vsync
# 640x480 @ 85Hz (VGA VESA 85) hsync: 43.3kHz
ModeLine "640x480" 36.0 640 696 752 832 480 481 484 509 \
-hsync -vsync
# 720x400 @ 85Hz (VESA 85) hsync: 37.9kHz
ModeLine "720x400" 35.5 720 756 828 936 400 401 404 446 \
-hsync +vsync
# 800x600 @ 56Hz (SVGA VESA 56) hsync: 35.2kHz
ModeLine "800x600" 36.0 800 824 896 1024 600 601 603 625 \
+hsync +vsync
# 800x600 @ 60Hz (SVGA VESA 60) hsync: 37.9kHz
ModeLine "800x600" 40.0 800 840 968 1056 600 601 605 628 \
+hsync +vsync
# 800x600 @ 72Hz (SVGA VESA 72) hsync: 48.1kHz
ModeLine "800x600" 50.0 800 856 976 1040 600 637 643 666 \
+hsync +vsync
# 800x600 @ 75Hz (SVGA VESA 75) hsync: 46.9kHz
ModeLine "800x600" 49.5 800 816 896 1056 600 601 604 625 \
+hsync +vsync
# 800x600 @ 85Hz (SVGA VESA 85) hsync: 53.7kHz
ModeLine "800x600" 56.3 800 832 896 1048 600 601 604 631 \
+hsync +vsync
# 1024x768 @ 43Hz (industry standard) hsync: 35.5kHz
ModeLine "1024x768" 44.9 1024 1032 1208 1264 768 768 776 817 \
+hsync +vsync Interlace
# 1024x768 @ 60Hz (XGA VESA 60) hsync: 48.4kHz
ModeLine "1024x768" 65.0 1024 1048 1184 1344 768 771 777 806 \
-hsync -vsync
# 1024x768 @ 70Hz (VESA 70, HP1070) hsync: 56.5kHz
ModeLine "1024x768" 75.0 1024 1048 1184 1328 768 771 777 806 \
-hsync -vsync
# 1024x768 @ 75Hz (XGA VESA 75) hsync: 60.0kHz
ModeLine "1024x768" 78.8 1024 1040 1136 1312 768 769 772 800 \
+hsync +vsync
# 1024x768 @ 85Hz (XGA VESA 85) hsync: 68.7kHz
ModeLine "1024x768" 94.5 1024 1072 1168 1376 768 769 772 808 \
+hsync +vsync
# 1152x864 @ 75Hz (SXGA VESA 75) hsync: 67.5kHz
ModeLine "1152x864" 108.0 1152 1216 1344 1600 864 865 868 900 \
+hsync +vsync
# 1280x960 @ 60Hz (SXGA VESA 60) hsync: 60.0kHz
ModeLine "1280x960" 108.0 1280 1376 1488 1800 960 961 964 1000 \
+hsync +vsync
# 1280x960 @ 85Hz (SXGA VESA 85) hsync: 85.9kHz
ModeLine "1280x960" 148.5 1280 1344 1504 1728 960 961 964 1011 \
+hsync +vsync
If you didn't find your display's resolution in this list, there are more standard modes listed at:
http://m.domaindlx.com/LinuxHelp/resources/modelines.htm
Another way to determine the display's modeline is to use the modeline calculator at:
http://xtiming.sourceforge.net/cgi-bin/xtiming.pl
Instead of determining the maximum refresh rate for your display, this will let you put in an arbitrary refresh rate and calculate the modeline from that. You can try a few until you arrive at one that seems likely to work with your display (again, a higher refresh rate is more desirable, since it provides a more flicker-free display but just getting the display to work is our goal here so beggars cannot be choosers).
Now, you can hack the Monitor section of the xorg.conf file in /etc/X11 and set the device identification fields to something useful (here we're using the recalcitrant Syntax LT27HV as an example):
Identifier "Syntax LT27HV LCD Display"
VendorName "Syntax"
ModelName "Olevia LT27HV"
Next, you should probably set the minimum and maximum horizontal and vertical sync frequencies from the chart of your display's capabilities:
HorizSync 56-87
VertRefresh 24-72
These values are not used to calculate any actual display settings but the values in the modelines are checked against these limits to ensure that you do not exceed your display's capabilities (and possibly destroy it).
Then, add the modelines to the Monitor section:
# 640x480 @ 85Hz (VGA VESA 85) hsync: 43.3kHz
ModeLine "640x480-85" 36.0 640 696 752 832 480 481 484 509 -hsync -vsync
# 800x600 @ 85Hz (SVGA VESA 85) hsync: 53.7kHz
ModeLine "800x600-85" 56.3 800 832 896 1048 600 601 604 631 +hsync +vsync
# 1024x768 @ 85Hz (XGA VESA 85) hsync: 68.7kHz
ModeLine "1024x768-85" 94.5 1024 1072 1168 1376 768 769 772 808 \
+hsync +vsync
# 1280x720 @ 60Hz (1280x720-60) vsync: 60.39Hz, hsync: 45.72kHz, clk: 74.25
# This is the only true native mode for the LT27HV display.
Modeline "1280x720-60" 74.25 1280 1312 1592 1624 720 735 742 757 \
+hsync +vsync
For the Syntax Olevia models, you may want to add the following, as well:
# Power saving mode
Option "DPMS"
# We know everything about this display
Option "UseEDID" "false"
# We know what the dot pitch is
Option "DPI" "96×96"
# Make sure the video card always picks the CRT. Or, if you have the
# display plugged in on the DVI connection, use "DFP" instead of "CRT-0".
Option "UseDisplayDevice" "CRT-0"
Next, hack the Screen section to use the display that you just defined by setting the Display SubSection to point to it:
# The color depth
Depth 24
# All of the supported modes that we defined in modelines. The first is
# the default mode chosen at startup.
Modes "1280x720-60" "1024x768-85" "800x600-85" "640x480-85"
Providing the display driver respects the ModeLine parameters (some of the nVidia drivers don't), you should now be in business. Unmount the partition from Knoppix, shut Knoppix down and reboot to see if it really works.