Final Answer:
b. The reason why a penetration tester would run the chkconfig --del servicename command at the end of an engagement is to disable unnecessary services.
Step-by-step explanation:
Penetration testers assess the security of a system and aim to identify vulnerabilities that malicious actors could exploit. Option b, disabling unnecessary services using chkconfig --del servicename, aligns with best practices for security testing.
By turning off services that are not essential for system functionality, the penetration tester helps reduce the attack surface and potential points of exploitation. This action enhances the overall security posture of the system. Running such commands is a proactive measure to mitigate security risks and is not associated with installing rootkits, escalating privileges, or performing denial-of-service (DoS) attacks.
Option B (To disable unnecessary services) is the answer.