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JSI Tip 3522. How do I disable the POSIX and OS2 sub-systems?

The POSIX and OS2 subsystems don't take any resources until an application that uses them is started.

If you open %SystemRoot%\System32\Config.NT, you will see the following comment:

REM By default, you can start any type of application when running
REM COMMAND.COM. If you start an application other than an MS-DOS-based
REM application, any running TSR may be disrupted. To ensure that only
REM MS-DOS-based applications can be started, add the command dosonly to
REM CONFIG.NT or other startup file.
You can disable these optional subsystems by using Regedt32 to navigate to:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Subsystems

Select the Posix and/or Os2 value names and delete them.

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