Microsoft KB Archive/174633

= Windows NT May Appear To Be Hung with Kernel Debugger =

Article ID: 174633

Article Last Modified on 10/31/2006

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APPLIES TO


 * Microsoft Windows NT Workstation 3.51
 * Microsoft Windows NT Workstation 4.0 Developer Edition
 * Microsoft Windows NT Server 3.51
 * Microsoft Windows NT Server 4.0 Standard Edition

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This article was previously published under Q174633



SUMMARY
A computer running Windows NT version 3.51 or 4.0, appears to stop responding (hang). There is no network connectivity to the computer, and there is no mouse cursor movement or keyboard input.



CAUSE
If the kernel-mode debugger is enabled on the affected computer, (the computer is booted in debug mode) then the following could be causing the computer to stop responding:

A DebugBreak function was called by a Win32 app and there is no user-mode debugger specified on the computer. The int 3 will be reflected into the kernel-mode debugger, causing the computer to appear like it has stopped responding. Going to the computer's kernel debugger will show that the computer is at a ntdll!DebugBreakPoint. Simply pressing "g" and Enter will release the kernel debugger.

For more information on the kernel debugger, see the following Microsoft Knowledge Base articles:

ARTICLE-ID: 148954

TITLE : How to Set Up a Remote Debug Session Using a Modem

ARTICLE-ID: 151981

TITLE : How to Set Up a Remote Debug Session Using a Null Modem Cable

For information on how to set up a user-mode debugger, see the following Microsoft Knowledge Base article:

ARTICLE-ID: 121434

TITLE : Specifying the Debugger for Unhandled User Mode Exceptions



MORE INFORMATION
When a Win32 user-mode application calls the DebugBreak function, the application causes a breakpoint exception to occur in the current process so that the calling thread can signal the debugger and force it to take action.

If there is no user-mode debugger specified to catch the int 3, and the kernel-mode debugger is enabled on the computer, the int 3, will be reflected into kernel-mode debugger and as a result, the computer appears to stop responding.

Additional query words: debugref

Keywords: kbprb KB174633

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