Final answer:
The distributed file system protocol used with UNIX and Linux file server clients is NFS (Network File System), which enables network file access similar to local file access.
Step-by-step explanation:
The distributed file system protocol used to access files over the network that is used with UNIX and Linux file server clients is NFS, which stands for Network File System. NFS allows a user on a client computer to access files over a network much like local storage is accessed. NFS was originally developed by Sun Microsystems in the 1980s and has since become a standard protocol used in UNIX and Linux systems.
Other options like DFS (Distributed File System) and SMB (Server Message Block) are more commonly associated with Windows environments, while DNS (Domain Name System) is a protocol used to resolve human-readable domain names to IP addresses and is not a file system protocol.