UUCPs

UUCPs, short for Unix-to-Unix Copy Protocols, refers to a family of programs and protocols developed for transferring files, email, and Usenet news between Unix and other systems over store-and-forward connections. Originating in the late 1970s and widely used through the 1980s and early 1990s, UUCP enabled asynchronous communication across dial-up modems, direct serial links, and later early network links when continuous connectivity was unavailable.

Key components include uucico, the transfer daemon that handles communication sessions; uucp, which initiates file copies; uux, which executes commands on remote systems; and cu, a basic terminal program. Configuration relies on a set of files describing remote systems (Systems), permissions (Permissions), dialing information (Dialers), and device definitions. Routing often used bang paths to specify routes, for example host1!host2!host3.

UUCP supports three major activities: file transfer, mail delivery, and Usenet netnews propagation. Tasks are queued on a local spool and transferred when a link becomes available. Transfers are batch-oriented and designed for low-bandwidth, high-latency environments, with basic error recovery and retry logic. Security is limited; authentication is typically based on trust relationships and simple permission files rather than encryption.

With the rise of TCP/IP Internet protocols, UUCP's prominence declined from the 1990s onward. Some systems retain UUCP for compatibility, historical research, or specialized use cases such as offline mail relays or amateur radio networks, sometimes running UUCP over modern transports like VPN or SSH.