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Legacy NVidia Ubuntu woes

March 11, 2008 By: webmaster Category: Technology, Ubuntu

Somewhere along the line, NVidia got a lot stricter in their monitor handling. If you used to be able to run X at high resolutions but all you can get after an upgrade is something like 1024×768 then it is likely that you have been caught by the clock check bug. You typically get lines like these in your Xorg log (/var/log/Xorg.0.log):

(WW) NVIDIA(0): No valid modes for "1920x1200"; removing.
(WW) NVIDIA(0): No valid modes for "1600x1200"; removing.

To get the X server to tell you exactly why it’s removing those two modes, try starting X with -logverbose 6 as arguments, and it will log something like this instead:


    (II) NVIDIA(0): Validating Mode "1600x1200":
    (II) NVIDIA(0): 1600 x 1200 @ 60 Hz
    (II) NVIDIA(0): For use as DFP backend.
    (II) NVIDIA(0): Mode Source: EDID
    (II) NVIDIA(0): Pixel Clock : 162.00 MHz
    (II) NVIDIA(0): HRes, HSyncStart : 1600, 1664
    (II) NVIDIA(0): HSyncEnd, HTotal : 1856, 2160
    (II) NVIDIA(0): VRes, VSyncStart : 1200, 1201
    (II) NVIDIA(0): VSyncEnd, VTotal : 1204, 1250
    (II) NVIDIA(0): H/V Polarity : +/+
    (WW) NVIDIA(0): Mode is rejected: PixelClock (162.0 MHz) too high for
    (WW) NVIDIA(0): Display Device (Max: 150.0 MHz).

If this used to work for you, and all you did was upgrade Ubuntu (or some other distro), then edit your /etc/X11/xorg.conf file and add the line

Option         "ModeValidation" "NoMaxPClkCheck"

inside either the Screen or the Device group. Restart X and it should start up in a higher mode again. For more interesting options to set, try looking at the NVidia X driver documentation.

Leave a comment if you’re lost and I’ll try to guide you through the tricky parts.

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