This security setting determines which subsystems can optionally be started up to support your applications. With this security setting, you can specify as many subsystems to support your applications as your environment demands. Default: POSIX. Note: When you configure this setting you specify a list of one or more objects. The delimiter used when entering the list is a line feed or carriage return, that is, type the first object on the list, press the Enter button, type the next object, press Enter again, etc. The setting value is stored as a comma-delimited list in group policy security templates. It is also rendered as a comma-delimited list in Group Policy Editor's display pane and the Resultant Set of Policy console. It is recorded in the registry as a line-feed delimited list in a REG_MULTI_SZ value. Counter Measure: Configure the System settings: Optional subsystems setting to a null value. The default value is POSIX. Potential Impact: Applications that rely on the POSIX subsystem will no longer operate. For example, Microsoft Services for Unix (SFU) installs an updated version of the POSIX subsystem that is required, so you would need to reconfigure this setting in a Group Policy for any servers that use SFU. Fix: (1) GPO: Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options\System settings: Optional subsystems (2) REG: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\SubSystems!optional