Leaving VGA cable plugged in during boot, scrambles image....

[ihelpmathgeeks]

Hello,

So this is a new problem for me. I'm running XCP-NG (Xen based on CentOS) on some Dell R620 servers.

I've had a weird problem, where periodically the image after boot would be all messed up (almost like an invalid refresh rate).

I then had an opportunity to install Debian 11, and I didn't seem to have the problem at all.

What is interesting, if I boot without the VGA cable plugged in, and then attach it after its done booting, the image is totally fine. Has anybody heard of this problem before?

Or what a good solution is? (besides swapping the VGA cable).

 

[mattventura]

I have seem some VGA devices do this. If you boot with no monitor plugged in, thus no EDID to read from, it will enable only the "more compatible" resolutions (like 640x480, 800x600, etc) with standard refresh rates. If you boot with something plugged in, it will try to use the EDID of whatever you plugged in.

It sounds like it's most likely an incompatibility between CentOS+the VGA chip+the monitor. There's also likely boot and bootloader options you could play around with, like disabling KMS, forcing a particular resolution, or making Linux use the default VGA driver instead of something specific to that chip.