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NT Gatekeeper: Disable an NT Server's OS/2 Subsystem

Helen Custer's book Inside Windows NT (Microsoft Press, 1992) says NT 4.0 includes an OS/2 subsystem, which you can use to run OS/2 applications on top of NT. My company completed the migration from OS/2 to NT 2 years ago; last year, I replaced the final OS/2 application with a Win32-based application. Now, I want to disable the OS/2 subsystem on my NT servers. What's the easiest way to disable OS/2?

Disabling or removing unused services, applications, or files is wise and especially important for the NT servers in your demilitarized zone (DMZ). Servers in the DMZ are more vulnerable to external attacks than are servers in your organization's trusted security zone. Follow these steps to disable the OS/2 subsystem on an NT system:

  1. Delete the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\SubSystems\Os2 registry subkey from the system registry. This subkey contains a path to the OS/2 subsystem executable file (i.e., os2ss.exe).
  2. Delete the os2.exe, os2srv.exe, and os2ss.exe files from your system. These files reside in the \%systemroot%\winnt\system32 folder. Os2.exe is the OS/2 subsystem client executable, and os2srv.exe is the OS/2 subsystem server executable.
  3. Delete the os2 folder in \%systemroot%\winnt\system32. The folder contains OS/2-specific DLLs.

If you don't use DOS, POSIX, or Win16 applications anymore, you can disable these subsystems with steps similar to those for disabling the OS/2 subsystem. However, use caution if you remove the DOS and Win16 subsystems: Some Win32 applications might still rely on DOS or Win16 subsystem files.

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