UUCP

From Free net encyclopedia

UUCP stands for Unix to Unix CoPy. The term generally refers to a suite of computer programs and protocols allowing remote execution of commands and transfer of files, 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 uuxqt (user interface for remote command execution), uucico (communication program), uustat (reports statistics on recent activity), 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 and Digital's VAX/VMS.

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Technology

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.

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History

UUCP was originally written at AT&T Bell Laboratories, 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 Utiltites"). All of these versions had security holes which allowed some of the original internet worms to remotely execute unexpected shell commands, which inspired 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. 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.

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

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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!you would refer to user you 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 adjacent to mine, but I know that barbox is adjacent to foovax and my machine talks to foovax, I would send mail to foovax!barbox!you.

User barbox!you might publish their UUCP e-mail address in a form such as ...!bigsite!foovax!barbox!you . This directs people to route their mail to machine bigsite (presumably a well-known location accessible to everybody) and from there through the machine foovax to the account of user you on barbox. People often published compound bang addresses using the { } convention (see glob) to give paths from several big machines, in the hopes that one's correspondent might be able to get mail to one of them reliably (example: ...!{seismo, ut-sally, ihnp4}!rice!beta!gamma!me). Bang paths of 8 to 10 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.

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.

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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 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.

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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 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.

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Decline

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

Usenet traffic was originally carried over the UUCPNET, and bang paths are still in use within the Usenet message format Path headers. 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 SMTP "@ notation", even by sites still using uucp.

Currently UUCP is used mainly over high cost links e.g. marine satellite links.

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See also

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External links

fr:Unix to Unix Copy Protocol nl:Unix to Unix Copy ja:Unix to Unix Copy Protocol pl:UUCP pt:UUCP ru:UUCP zh:UUCP

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