By configuring Pluggable Authentication Module (PAM) and Name Service Switch (NSS) to use OpenLDAP, which authentication service can be replaced?

Configuring Pluggable Authentication Module (PAM) and Name Service Switch (NSS) to utilize OpenLDAP provides an alternative to the traditional Network Information Service (NIS). NIS, which was widely used for providing centralized authentication and directory services, can be limited in scalability and security. By implementing OpenLDAP, which is more modern and robust, you can effectively replace NIS as it allows for a more secure and flexible way of handling user authentication and information storage.

Using OpenLDAP in this context means that user credentials and other directory information are stored in an LDAP directory, allowing applications and services to authenticate against it. This shift enhances security through features like SSL/TLS encryption and opens up the possibility for integration with a diverse set of services beyond just UNIX-like systems.

The other options are not directly replaced by configuring PAM and NSS with OpenLDAP. For instance, Microsoft NT Domain, Samba, and Active Directory (AD) serve different roles in authentication and directory services, particularly in Windows or mixed environments. They focus more on domain services and resource management rather than solely on user credential storage like NIS. Therefore, NIS is the primary service that is effectively replaced by the OpenLDAP configuration in this scenario.