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Unix-to-Unix copy (UUCP) is a set of computer programs and protocols that allow for the remote execution of commands and the transfer of email and files between computers.
UUCP is presently used over TCP/IP. UUCP's longevity may be attributed to to extensive logging, persistent queue management and low cost.
The UUCP suite includes:
The first version of UUCP was called System V UUCP and was developed at AT&T Bell Laboratories by Mike Lesk. Because the initial versions were not distributed with source code, a new version was produced under GNU General Public License. This version was extremely stable and bug free. UUCP implementations also exist for operating systems such as VAX/VMS, AmigaOS, Mac OS and MS DOS.
UUCP houses several link-layer protocols and physical connections. Before the Internet, systems were connected by small networks within an organization and were equipped with modems to be used remotely through dial-up lines. UUCP used the computer modems to dial other computers, creating point-to-point links between them.
Every system in a UUCP network includes neighbor systems that contain login names, passwords and phone numbers. When a job is waiting for a neighbor system, the uucico process calls the respective system to process the job. It also polls nearby systems frequently to check for queued jobs. This allows the systems without dial-out capability to participate in the process.
UUCP and its uuxt are used to transfer emails with proper mail user interface and delivery agent programs. The uucp mail address is formed from an adjacent machine name, an exclamation mark (bang) and the user name from the adjacent machine. Initially, pseudo names ending with .uucp designated host names are reachable through UUCP networking. If a .uucp address is encountered in an incoming Simple Mail Transfer Protocol (SMTP) connection, the host normally transfers mail from SMTP queues into uucp queues on gateway machines.