Dual decor capability for a host system which runs emulated application programs to enable direct access to host facilities for executing emulated system operations

A host data processing system which includes a plurality of input/output devices operates under the control of an enhanced version of the UNIX operating system. The host system includes an emulator which runs as an application process for executing user emulated system (ES) application programs. The emulator includes a number of emulated system executive service components operating in shared memory and an interpreter, an emulator monitor call unit (EMCU) and a number of server facilities operating in the host memory. The ES executive service components are extended to accommodate a number of dual decor commands and functions which make host system facilities directly available to ES application programs by concurrent execution of program operations within both the emulator and host system environments. The EMCU includes mechanisms for performing an initial level security validation operation which allows subsequent trusted verification of user identity when dual decor commands or functions are invoked. The server facilities include mechanisms for performing a two-step security validation process for ensuring security relative to preventing both unauthorized user access and compromises in user data through improper use of dual decor commands or functions.