On my Ubuntu installation, my installation was recently (and automatically) upgraded to 352.63 due to a security fix from version 346.xx, which is no longer available in the repositories. Before the upgrade my xorg.conf with custom modelines was working perfectly, but after reboot X no longer started. Looking at the log file it seems that X cannot find any valid modes for my screen anymore, which is strange because the log also states “Mode X is valid” for all my custom modelines. I removed the NoEdidModes mode validation option, and suddenly it works again including my custom modelines, but now I have a bunch of EDID modes that I don’t want. This might not seem like a big deal but for my setup to work optimally I need to make sure X ONLY uses the modelines that I specify manually, because the EDID-modes are sub-optimal (for example outputs 23.971 Hz instead of 23.976).
Steps to reproduce
Use a custom ModeLine corresponding to an EDID mode present in your hardware in the “Monitor” section, e.g.
ModeLine "1920x1080p_60" 148.500 1920 2008 2052 2200 1080 1084 1089 1125 +hsync +vsync
It’s imperative that the timings match the mode in your hardware’s EDID exactly to reproduce the bug. They can be extracted using the “get-edid” and “edid-decode” commands available in the Ubuntu repositories.
Then, put this in the “Screen” section
Option "ExactModeTimingsDVI" "true" Option "ModeValidation" "NoVesaModes, NoXServerModes, NoPredefinedModes, NoEdidModes, NoUserModes"
and restart X. On Ubuntu 14.04, press Ctrl+Alt+SysRq+K to kill everything in the current session (lightdm/X will be restarted automatically)
switch to tty1 (Ctrl+Alt+F1), login and run
sudo service lightdm stop sudo service lightdm start
X should start normally with the screen set to the specified mode.
Startup fails and X goes into failsafe mode.
nvidia-bug-report.log.gz (88.9 KB)