Windows NT May Appear To Be Hung with Kernel Debugger

• Microsoft Windows NT Workstation versions 3.51, 4.0
• Microsoft Windows NT Server versions 3.51, 4.0

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: Q148954
TITLE : How to Set Up a Remote Debug Session Using a Modem

ARTICLE-ID: Q151981
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: Q121434
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 : nt32ap NTSrvWkst
Version : WinNT:3.51,4.0
Platform : winnt
Issue type : kbprb