Final answer:
The RACF administrator's primary duty is Security Planning, focusing on defining access rights, maintaining user profiles, and enforcing security policies in z/OS mainframe environments.
Step-by-step explanation:
The main responsibility of the RACF (Resource Access Control Facility) administrator is Security Planning. RACF is a security tool used in z/OS systems that provides access control and auditing functionality. The administrator's duties include defining and managing access rights to resources, ensuring system security by creating and maintaining user profiles, and enforcing access policies.
While software installation, program debugging, and job scheduling are important tasks within an IT environment, they are not the primary responsibilities of a RACF administrator, whose focus is on securing the mainframe environment and its resources.