uucp

UUCP, or Unix-to-Unix Copy, is a suite of programs and a set of protocols that enabled the transfer of files, email, and Usenet news between computers running Unix or Unix-like systems. Developed in the 1970s, it operates over dial-up, serial, or network links and uses a store-and-forward model, queuing data on each machine until a connection to a remote system becomes available.

Key components include uucp for file transfers, uux for remote command execution, and cu or tip for terminal connections. Local mail and news handling programs integrate with UUCP to support messaging and distribution. Data is staged in spool directories and transferred in batches; routing scripts determine destinations. Addressing often used bang paths, such as host1!host2!user, to indicate routes.

UUCP enabled distributed mail and Usenet distribution long before standard Internet protocols. It supported asynchronous operation and was widely used in academic, hobbyist, and corporate networks, linking disparate systems by phone lines or simple networks. The model allowed networks to expand without a centralized backbone and fostered early email and newsgroup exchanges across large geographies.

With the growth of TCP/IP and modern mail and NNTP protocols, UUCP’s prominence declined during the 1990s and beyond. It remains in use on legacy systems and in some specialized deployments, and there are modern implementations that run UUCP over TCP/IP or bridge it with contemporary mail and news software for archival or interoperability purposes.