Final Answer:
In addition to the internal authentication via etcpasswd and etcshadow files, LDAP, Kerberos, RADIUS, TACACS+ can be used to authenticate users to a Linux host. Thus. the correct answer is (C) LDAP, Kerberos, RADIUS, TACACS+.
Step-by-step explanation:
In addition to the traditional internal authentication via 'etcpasswd' and 'etcshadow' files on a Linux host, multiple services can be utilized to authenticate users. These services include LDAP (Lightweight Directory Access Protocol), Kerberos, RADIUS (Remote Authentication Dial-In User Service), and TACACS+ (Terminal Access Controller Access-Control System Plus). Each of these services offers distinct authentication mechanisms that can be employed for user verification and access control on a Linux system.
LDAP serves as a protocol for accessing and managing directory services. It can be used to authenticate and authorize users by querying a centralized directory server containing user information. Kerberos is a network authentication protocol that uses strong encryption to validate users and provide secure authentication for network services.
RADIUS is commonly employed in remote authentication scenarios, such as dial-up connections or wireless networks, managing authentication, authorization, and accounting information. TACACS+ is a security protocol commonly used for device administration, allowing granular control over user access and authentication.
These services enhance security and flexibility in user authentication beyond the traditional local file-based authentication mechanisms ('etcpasswd' and 'etcshadow'). By integrating LDAP, Kerberos, RADIUS, and TACACS+, administrators can centralize user authentication, enforce stricter security policies, and manage user access efficiently across a networked environment, providing multiple layers of authentication and authorization for Linux systems.
Thus. the correct answer is (C) LDAP, Kerberos, RADIUS, TACACS+.