PrintScreen magic

Do you want to play a really nasty joke on your good friend?

Well, here's the deal: When a Windows computer has booted in DEBUG mode (/DEBUG and friends in boot.ini entry) then pressing PrintScreen causes a kernel breakpoint, bringing the machine to a complete halt, so that the kernel debugger can operate on it. Now, isn't that cool?

If you are not at ease touching BOOT.INI or using the dreaded BCDEDIT in Vista, then use MSCONFIG.EXE at your leisure.

So set your friends machine to boot in debug mode and rest back, waiting for him to try to get a screenshot. Alt+PrintScreen won't trigger the breakpoint. It happened to me twice, before I realized what on earth was happening.

Here is the message in the Kernel Debugger that welcomes you when you connect to a debug PC that has been frozen with PrintScreen:

*******************************************************************************
*
*   You are seeing this message because you pressed the SysRq/PrintScreen
*   key on your test machine's keyboard.
*
*                   THIS IS NOT A BUG OR A SYSTEM CRASH
*
* If you did not intend to break into the debugger, press the "g" key, then
* press the "Enter" key now.  This message might immediately reappear.  If it
* does, press "g" and "Enter" again.
*
*******************************************************************************

The funny thing is that even simple user mode asserts and unhandled exceptions will break into the kernel debugger. So some application crashes, Windows freezes, and your friend is wondering whether he should move to Linux ;-)

Have fun,
Dimitris Staikos