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I am using Ubuntu Linux 11.10. Currently, I have Windows XP on one computer, and Ubuntu on another. I switch between the with a VGA box that allows me to switch which computer is connected to my monitor. For some reason, if I am viewing Windows XP while Ubuntu is booting, the screen will be black when I switch back over to it. I have waited 15 minutes on this screen, and nothing happened. I have also tried to "wake it up" by moving the mouse and using the keyboard. Ubuntu boots fine if it is connected to the monitor when it boots. Does anyone know what could be causing this?

The output of lspci -nn | grep VGA is:

00:02.0 VGA compatible controller [0300]: Intel Corporation 82915G/GV/910GL Integrated Graphics Controller [8086:2582] (rev 04)

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possible duplicate of How can I force X to start in a computer without a monitor? –  Javier Rivera Jan 20 '12 at 15:14

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up vote 2 down vote accepted

I would like to give an educated guess based upon my own experience with a video card that overheated causing Ubuntu to fail to load because it could not determine the correct screen resolution.

When we install Ubuntu we are not required to set the screen resolution. Are we? So, how does the OS know the correct or optimum resolution of the monitor.

The OS interrogates the monitor to find the EDID. A quote from EDID Wikipedia

Extended display identification data (EDID) is a data structure provided by a digital display to describe its capabilities to a video source (e.g. graphics card or set-top box). It is what enables a modern personal computer to know what kinds of monitors are connected to it. EDID is defined by a standard published by the Video Electronics Standards Association (VESA). The EDID includes manufacturer name and serial number, product type, phosphor or filter type, timings supported by the display, display size, luminance data and (for digital displays only) pixel mapping data.

To confirm this I quote Ubuntu wiki under the heading Adding Undetected Resolutions

Due to buggy hardware or drivers, your monitor’s correct resolutions may not always be detected. For example, the EDID data block queried from your monitor may be incorrect.

In your case, when Ubuntu loads it cannot read the monitor's EDID block because you have not switched the monitor over to Ubuntu.

That switch box works by effectively unplugging the monitor from one machine and plugging it into an other machine. The switch that you turn physically cuts the cable from the VGA port on one machine and makes a connection to the VGA port on the other machine.

I would guess that anyone booting Ubuntu without the monitor connected would have the same problem that you are having.

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Thank you! I was confused as to why switching the monitor or effectively unplugging it would make the screen go black. Thank you for explaining this to me! –  Aaron Jan 21 '12 at 12:59

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