The user ID routine returns the same value as the USERID built-in function. The system calls the user ID replaceable routine whenever the USERID built-in function is issued in a language processor environment that is not integrated into TSO/E. The routine then returns either the user ID, stepname, or jobname. The name of the system-supplied user ID routine is IRXUID.

The name of the user ID replaceable routine is specified in the IDROUT field in the module name table. Module name table describes the format of the module name table.