UUCP (UNIX-to-UNIX Copy Protocol) is a set of UNIX programs for copying (sending) files between different UNIX systems and for sending commands to be executed on another system. The main UUCP commands (each supported by a UUCP program) are:
- uucp, which requests the copying of a specific file to another specified system
- uux, which sends a UNIX command to another system where it is queued for execution
- uucico, which runs on a UNIX system as the program that carries out the copying and initiates execution of the commands that have been sent. Typically, this program is run at various times of day; meanwhile, the copy (uucp) and command (uux) requests are queued until the uucico program is run.
- uuxqt, which executes the commands sent by uux, usually after being started by the uucico program
The uucico programs are the programs that actually communicate across a network. There are several network protocols (variations on packet size and error-checking) that can be used by uucico programs, depending on the kinds of carrier networks being used.