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UUCP is an abbreviation for Unix-to-Unix Copy. The term generally refers to a suite of computer programs and protocol allowing remote execution of commands and transfer of file, email and netnews between computers. Specifically, UUCP is one of the programs in the suite; it provides a user interface for requesting file copy operations. The UUCP suite also includes uux (user interface for remote command execution), uucico (communication program), uustat (reports statistics on recent activity), uuxqt (execute commands sent from remote machines), and uuname (reports the uucp name of the local system).

Although UUCP was originally developed on and is most closely associated with Unix, UUCP implementations exist for several other operating systems, including Microsoft's MS-DOS, Digital's VAX/VMS, Commodore's AmigaOS, and Mac OS.


UUCP can use several different types of physical connections and link layer protocols, but was most commonly used over dial-up connections. Before the widespread availability of Internet connectivity, computers were only connected by smaller private networks within a company or organization. They were also often equipped with modems so they could be used remotely from character-mode terminals via dial-up lines. UUCP uses the computers' modems to dial out to other computers, establishing temporary, point-to-point links between them. Each system in a UUCP network has a list of neighbor systems, with phone numbers, login names and passwords, etc. When work (file transfer or command execution requests) is queued for a neighbor system, the uucico program typically calls that system to process the work. The uucico program can also poll its neighbors periodically to check for work queued on their side; this permits neighbors without dial-out capability to participate.

Today, UUCP is rarely used over dial-up links, but is occasionally used over TCP/IP.

One example of the current use of UUCP is in the retail industry by Epicor CRS Retail Systems for transferring batch files between corporate and store systems via TCP and dial-up on SCO OpenServer, Red Hat Linux, and Microsoft Windows (with Cygwin). The number of systems involved, as of early 2006, ran between 1500 and 2000 sites across 60 enterprises. UUCP's longevity can be attributed to its low/zero cost, extensive logging, native failover to dialup, and persistent queue management.


UUCP was originally written at AT&T Bell Laboratoriesmarker, by Mike Lesk, and early versions of UUCP are sometimes referred to as System V UUCP. The original UUCP was rewritten by AT&T researchers Peter Honeyman, David A. Nowitz, and Brian E. Redman and the rewrite is referred to as HDB or HoneyDanBer uucp which was later enhanced, bug fixed, and repackaged as BNU UUCP ("Basic Network Utilities"). None of these versions were distributed with source code, which inspired Ian Lance Taylor to write a new version from scratch.

Taylor UUCP was released under the GNU General Public License and became the most stable and bug free version. In particular Taylor UUCP addressed security holes which allowed some of the original internet worm to remotely execute unexpected shell commands. Taylor UUCP also incorporates features of all previous versions of UUCP, allowing it to communicate with any other version with the greatest level of compatibility and even use similar config file formats from other versions. UUCP was also implemented for non-UNIX operating systems, most-notably MS-DOS systems. Packages such as UUSLAVE/GNUCICO (John Gilmore, Garry Paxinos, Tim Pozar), UUPC (Drew Derbyshire) and FSUUCP (Christopher Ambler of IODesign, - ".web" tld of the 1990s), brought early Internet connectivity to personal computers, expanding the network beyond the interconnected university systems. FSUUCP formed the basis for many BBS packages such as Galacticomm's Major BBS and Mustang Software's Wildcat! BBS to connect to the UUCP network and exchange email and Usenet traffic. As an example, UFGATE (John Galvin, Garry Paxinos, Tim Pozar) was a package that provided a gateway between networks running Fidonet and UUCP protocols.

FSUUCP was notable for being the only other implementation of Taylor's enhanced 'i' protocol, a significant improvement over the standard 'g' protocol used by most UUCP implementations.

One surviving feature of uucp is the chat file format, largely inherited by the expect software package.

UUCP for mail routing

The uucp and uuxqt capabilities could be used to send e-mail between machines, with suitable mail user interface and delivery agent programs. A simple uucp mail address was formed from the adjacent machine name, an exclamation mark or bang, followed by the user name on the adjacent machine. For example, the address barbox!user would refer to user user on adjacent machine barbox.

Mail could furthermore be routed through the network, traversing any number of intermediate nodes before arriving at its destination. Initially, this had to be done by specifying the complete path, with a list of intermediate host names separated by bangs. For example, if machine barbox is not connected to the local machine, but it is known that barbox is connected to machine foovax which does communicate with the local machine, the appropriate address to send mail to would be foovax!barbox!user.

User barbox!user might publish their UUCP email address in a form such as …!bigsite!foovax!barbox!user. This directs people to route their mail to machine bigsite (presumably a well-known and well-connected machine accessible to everybody) and from there through the machine foovax to the account of user user on barbox. Many users would suggest multiple routes from various large well-known sites, providing even better and perhaps faster connection service from the mail sender.

Bang paths of eight to ten machines (or hops) were not uncommon in 1981, and late-night dial-up UUCP links would cause week-long transmission times. Bang paths were often selected by both transmission time and reliability, as messages would often get lost. Some hosts went so far as to try to "rewrite" the path, sending mail via "faster" routes—this practice tended to be frowned upon.

The "pseudo-domain" ending .uucp was sometimes used to designate a hostname as being reachable by UUCP networking, although this was never formally in the Internet root as a top-level domain. This would not have made sense anyway, because the DNS system is only appropriate for hosts reachable directly by TCP/IP. Additionally, uucp as a community administers itself and does not mesh well with the administration methods and regulations governing the DNS; .uucp works where it needs to; some hosts punt mail out of SMTP queue into uucp queues on gateway machines if a .uucp address is recognized on an incoming SMTP connection

UUCPNET and mapping

UUCPNET was the name for the totality of the network of computers connected through UUCP. This network was very informal, maintained in a spirit of mutual cooperation between systems owned by thousands of private companies, universities, and so on. Often, particularly in the private sector, UUCP links were established without official approval from the companies' upper management. The UUCP network was constantly changing as new systems and dial-up links were added, others were removed, etc.

The UUCP Mapping Project was a volunteer, largely successful effort to build a map of the connections between machines that were open mail relays and establish a managed namespace. Each system administrator would submit, by e-mail, a list of the systems to which theirs would connect, along with a ranking for each such connection. These submitted map entries were processed by an automatic program that combined them into a single set of files describing all connections in the network. These files were then published monthly in a newsgroup dedicated to this purpose. The UUCP map files could then be used by software such as "pathalias" to compute the best route path from one machine to another for mail, and to supply this route automatically. The UUCP maps also listed contact information for the sites, and so gave sites seeking to join UUCPNET an easy way to find prospective neighbors.

Connections with the Internet

Many uucp hosts, particularly those at universities, were also connected to the Internet in its early years, and e-mail gateways between Internet SMTP-based mail and UUCP mail were developed. A user at a system with UUCP connections could thereby exchange mail with Internet users, and the Internet links could be used to bypass large portions of the slow UUCP network. A "UUCP zone" was defined within the Internet domain namespace to facilitate these interfaces.

With this infrastructure in place, UUCP's strength was that it permitted a site to gain Internet e-mail and Usenet connectivity with only a dial-up modem link to another cooperating computer. This was at a time when true Internet access required a leased data line providing a connection to an Internet Point of Presence, both of which were expensive and difficult to arrange. By contrast, a link to the UUCP network could usually be established with a few phone calls to the administrators of prospective neighbor systems. Neighbor systems were often close enough to avoid all but the most basic charges for telephone calls.


UUCP usage began to die out with the rise of ISP offering inexpensive SLIP and PPP services. The UUCP Mapping Project was formally shut down late in 2000.

The UUCP protocol has now mostly been replaced by the Internet TCP/IP based protocols SMTP for mail and NNTP Usenet news.

Usenet traffic was originally transmitted over the UUCP protocol using bang paths. These are still in use within Usenet message format Path header lines. They now have only an informational purpose, and are not used for routing, although they can be used to ensure that loops do not occur. In general, this form of e-mail address has now been superseded by the "@ notation", even by sites still using UUCP.

Current use

UUCP is used mainly over high cost links (e.g., marine satellite links). UUCP over TCP/IP (often encrypted, using the SSH protocol) can be used when a computer doesn't have any fixed IP addresses but is still willing to run a standard mail transfer agent (MTA) like Sendmail or Postfix.

See also


External links

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