Opening the program

1

Assume that an application program has been started. The program issues an OPEN macroinstruction to open an access method control block (ACB). The ACB, in the data declarations area of the program, enables VTAM® to relate the application program to the name of the APPL definition statement used by the system programmer to define the application program to VTAM.

VTAM verifies that a user is authorized to open a VTAM application ACB. VTAM does this by invoking the System Authorization Facility (SAF) router, which directs control to the installed security management product, such as the Resource Access Control Facility (RACF®), to perform the requested task. For information on how to use RACF for this security feature and what restrictions apply, refer to the z/OS Security Server RACF Security Administrator's Guide. For additional information on how SAF is invoked, refer to Opening an application program.

When the OPEN macroinstruction processing is completed, an SSCP-LU session is established between the SSCP and the application program LU. The SETLOGON macroinstruction is required to enable the LOGON exit routine to be driven when a CINIT is received.