Explanation
A zone file is a text file that defines a portion of the DNS namespace, called a zone. A zone file contains resource records that map domain names to IP addresses or other information. A zone file must follow the rules of the DNS hierarchy, which means that it can only contain records for names that are within the zone's domain. For example, a zone file for example.com can only contain records for names that end with example.com, such as www.example.com or mail.example.com. It cannot contain records for names that are outside the zone's domain, such as google.com or example.net. This is because the DNS server that hosts the zone file is only authoritative for the zone's domain, and not for any other domains. If a zone file contains records for names that are outside the zone's hierarchy, it will cause errors and inconsistencies in the DNS resolution process. References: LPIC-2 202 exam objectives, DNS zone file format, DNS hierarchy

Explanation
PAM modules are organized and stored as shared object files within the /lib/ directory hierarchy. A shared object file is a file that contains executable code and data that can be loaded into memory and used by one or more programs. This allows PAM modules to be dynamically loaded and unloaded by the PAM library as needed, without requiring recompilation or relinking of the programs that use them. The /lib/ directory hierarchy contains subdirectories for different architectures and operating systems, such as
/lib/x86_64-linux-gnu/ or /lib64/. The PAM modules are usually located in a subdirectory named security, such as /lib/x86_64-linux-gnu/security/ or /lib64/security/. The PAM modules have names that start with pam_ and end with .so, such as pam_unix.so or pam_cracklib.so12.
References:
PAM Modules: A section from the Linux-PAM System Administrators' Guide that explains what PAM modules are, how they are named, and where they are located.
An introduction to Pluggable Authentication Modules (PAM) in Linux: An article from Red Hat that introduces the concept and usage of PAM in Linux, which includes a description of PAM modules and their location.

Explanation/Reference:

Explanation/Reference:
Reference: https://openvpn.net/archive/openvpn-users/2006-04/msg00355.html