View source for UUCP

{{short description|Suite of computer programs and protocols}}
{{Infobox Software 
| name                   = UUCP
| logo                   = 
| screenshot             = 
| screenshot size        = 
| caption                = 
| author                 = [[Mike Lesk]]
| developer              = [[AT&T Bell Laboratories]]
| released               = {{Start date and age|1979}}
| latest release version = 
| latest release date    = 
| operating system       = [[Unix]] and [[Unix-like]], [[DOS]], [[OS/2]], [[OpenVMS]], [[AmigaOS]], [[classic Mac OS]], [[CP/M]]
| genre                  = [[Command (computing)|Command]]
| license                = 
| website                = 
}}
{{Internet history timeline}}

'''UUCP''' ('''Unix-to-Unix Copy''')<ref>{{cite book|title=UNIX(TM) TIME-SHARING SYSTEM: UNIX PROGRAMMER'S MANUAL, Seventh Edition, Volume 1|date=January 1979|publisher=Bell Telephone Laboratories, Incorporated|location=Murray Hill, New Jersey|url=http://web.cuzuco.com/~cuzuco/v7/v7vol1.pdf|access-date=2018-02-20|archive-date=2016-04-29|archive-url=https://web.archive.org/web/20160429022722/http://web.cuzuco.com/~cuzuco/v7/v7vol1.pdf|url-status=live}}</ref> is a suite of [[computer program]]s and [[communications protocol|protocol]]s allowing remote execution of commands and transfer of [[computer file|file]]s, [[email]] and [[netnews]] between [[computer]]s.

A command named {{code|uucp}} is one of the programs in the suite; it provides a user interface for requesting file copy operations.  The UUCP suite also includes {{code|uux}} (user interface for remote command execution), {{code|uucico}} (the communication program that performs the file transfers), {{code|uustat}} (reports statistics on recent activity), {{code|uuxqt}} (execute commands sent from remote machines), and {{code|uuname}} (reports the UUCP name of the local system).  Some versions of the suite include [[uuencoding|{{code|uuencode}}]]/{{code|uudecode}} (convert 8-bit binary files to 7-bit text format and vice versa).

Although UUCP was originally developed on [[Unix]] in the 1970s and 1980s, and is most closely associated with [[Unix-like]] systems, UUCP implementations exist for several non-Unix-like operating systems, including [[DOS]], [[OS/2]], [[OpenVMS]] (for VAX hardware only), [[AmigaOS]],<ref>{{Cite web | url=https://aminet.net/comm/uucp | title=Aminet - Search }}</ref> [[classic Mac OS]], and even [[CP/M]].

==History==
UUCP was originally written at [[AT&T Bell Laboratories]] by [[Mike Lesk]].<ref name="reader">{{cite tech report |first1=M. D. |last1=McIlroy |author-link1=Doug McIlroy |year=1987 |url=http://www.cs.dartmouth.edu/~doug/reader.pdf |title=A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 |series=CSTR |number=139 |institution=Bell Labs |access-date=2015-02-01 |archive-date=2017-11-11 |archive-url=https://web.archive.org/web/20171111151817/http://www.cs.dartmouth.edu/~doug/reader.pdf |url-status=live }}</ref> By 1978, it was in use on 82 UNIX machines inside the Bell system, primarily for software distribution.  It was released in 1979 as part of [[Version 7 Unix]].<ref>{{Cite web |url=http://a.papnet.eu/UNIX/v7/files/doc/36_uucpimp.pdf |title=Version 7 Unix manual: "UUCP Implementation Description" by D. A. Nowitz, and "A Dial-Up Network of UNIX Systems" by D. A. Nowitz and M. E. Lesk |access-date=2018-02-21 |archive-date=2018-02-21 |archive-url=https://web.archive.org/web/20180221100921/http://a.papnet.eu/UNIX/v7/files/doc/36_uucpimp.pdf |url-status=live }}</ref>

The first UUCP emails from the U.S. arrived in the United Kingdom in 1979 and email between the UK, the Netherlands and Denmark started in 1980, becoming a regular service via [[EUnet]] in 1982.<ref name=":22">{{Cite web |last=Houlder |first=Peter |date=19 January 2007 |title=Starting the Commercial Internet in the UK |url=https://www.uknof.org.uk/uknof6/Houlder-History.pdf |access-date=2020-02-12 |website=6th UK Network Operators' Forum}}</ref><ref name=":122">{{Cite web |last=Reid |first=Jim |date=3 April 2007 |title=Networking in UK Academia ~25 Years Ago |url=https://www.uknof.org.uk/uknof7/Reid-History.pdf |access-date=2020-02-12 |website=7th UK Network Operators' Forum |archive-date=2007-08-20 |archive-url=https://web.archive.org/web/20070820064908/http://www.uknof.org.uk/uknof7/Reid-History.pdf |url-status=dead }}</ref>

The original UUCP was [[Rewrite (programming)|rewritten]] by AT&T researchers Peter Honeyman, David A. Nowitz, and Brian E. Redman around 1983.  The rewrite is referred to as ''HDB'' or ''HoneyDanBer'' uucp, which was later enhanced, bug fixed, and repackaged as ''BNU UUCP'' ("Basic Network Utilities").<ref>{{Cite web |title= The History of ihnp4 and The Growth of the Email Network |author= Gary J. Murakami |date= September 24, 1988 |url= http://www.nobell.org/~gjm/about/ihnp4.html |access-date= June 7, 2013 |archive-date= September 11, 2013 |archive-url= https://web.archive.org/web/20130911062530/http://www.nobell.org/~gjm/about/ihnp4.html |url-status= live }}</ref> 

Each of these versions was distributed as proprietary software, which inspired [[Ian Lance Taylor]] to write a new [[free software]] version from scratch in 1991.<ref>{{cite web
|url=http://groups.google.com/group/comp.mail.uucp/browse_thread/thread/a59ccd63afcade57
|title=Beta release of new UUCP package available
|access-date= 2009-01-19
|author=Ian Lance Taylor
|date=September 1991
}}</ref>
''Taylor UUCP'' was released under the [[GNU General Public License]].  Taylor UUCP addressed security holes which allowed some of the original [[computer worm|network worm]]s to remotely execute unexpected shell commands. Taylor UUCP also incorporated features of all previous versions of UUCP, allowing it to communicate with any other version and even use similar config file formats from other versions.

UUCP was also implemented for non-[[UNIX]] operating systems, most-notably [[DOS]] systems. Packages such as UUSLAVE/GNUUCP ([[John Gilmore (activist)|John Gilmore]], Garry Paxinos, Tim Pozar), UUPC/extended (Drew Derbyshire of Kendra Electronic Wonderworks) and FSUUCP (Christopher Ambler of IODesign), brought early [[Internet]] connectivity to personal computers, expanding the network beyond the interconnected university systems. FSUUCP formed the basis for many [[bulletin board system]] (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 the only other implementation of Taylor's enhanced 'i' protocol, a significant improvement over the standard 'g' protocol used by most UUCP implementations.{{Citation needed |date= June 2013}}

==Technology==
Before the widespread availability of [[Internet access]], computers were only connected by smaller [[local area network]]s within a company or organization. They were also often equipped with [[modems]] so they could be used remotely from [[Character terminal#Dumb terminal|character-mode terminals]] via [[dial-up]] [[plain old telephone service|telephone lines]]. UUCP used 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 {{code|uucico}} program typically calls that system to process the work. The {{code|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.

Over time, dial-up links were replaced by Internet connections, and UUCP added a number of new [[link layer]] protocols. These newer connections also reduced the need for UUCP at all, as newer application protocols developed to take advantage of the new networks. Today, UUCP is rarely used over dial-up links, but is occasionally used over [[Internet protocol suite|TCP/IP]].<ref>{{cite web
|url=http://www.airs.com/ian/uucp-doc/uucp_7.html#SEC99
|title=UUCP 'f' Protocol
|access-date=2008-08-04
|author=Ian Lance Taylor
|date=June 2003
|archive-date=2008-07-18
|archive-url=https://web.archive.org/web/20080718235206/http://www.airs.com/ian/uucp-doc/uucp_7.html#SEC99
|url-status=live
}}</ref><ref name=UUCPssh>{{cite web
|url=http://uucpssh.org/
|title=UUCPssh
|access-date=2009-08-09
|author=Fabien Penso
|url-status=usurped
|archive-url=https://web.archive.org/web/20090930074051/http://www.uucpssh.org/
|archive-date=2009-09-30
}}</ref> 
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 cost, extensive logging, native [[failover]] to dialup, and persistent queue management.

===Sessions===
UUCP is normally started by having a user log into the target system and then running the UUCP program. In most cases, this is automated by logging into a known user account used for transfers, whose account's shell has been set to {{code|uucico}}. Thus, for automated transfers, another machine simply has to open a modem connection to the called machine and log into the known account.

When uucico runs, it will expect to receive commands from another UUCP program on the caller's machine and begin a session. The session has three distinct stages:

# Initial handshake
# File request(s)
# Final handshake

====Initial handshake====
On starting, uucico will respond by sending an identification string, <code>\20Shere=''hostname''\0</code>, where \20 is the control-P character, and \0 is a trailing null. The caller's UUCP responds with <code>\20S''callername'' ''options''\0</code>, where ''options'' is a string containing zero or more Unix-like option switches. These can include packet and window sizes, the maximum supported file size, debugging options, and others.

Depending on the setup of the two systems, the call may end here. For instance, when the caller responds with their system name, the called system may optionally hang up if it does not recognize the caller, sending the <code>RYou are unknown to me\0</code> response string and then disconnecting.

====File requests====
If the two systems successfully handshake, the caller will now begin to send a series of file requests. There are four types:

:'''S''' causes a file to be Sent from the caller to the called system (upload). The from and to names are provided, allowing the filename to be changed on the receiver. When the S command is received on the called system, it responds with SY if it succeeded and it is ready to accept the file, or SNx if it failed, where x is a failure code. If an SY is received by the caller, it begins uploading the file using the protocol selected during the initial handshake (see below). When the transfer is complete, the called system responds with CY if it successfully received the file, or CN5 if it failed.
:'''R''' is a Request for the called system to send a file to the caller (download). It is otherwise similar to S, using RY and RN to indicate the command was accepted and it will begin to send data or had a problem, and expecting a CY and CN5 from the caller at the end of the transfer.
:'''X''' uploads commands to be eXecuted on the called system. This can be used to make that system call another and deliver files to it. The called system responds with XY if it succeeded, or XN if it failed.
:'''H''', for Hangup, indicates the caller is done. The called system responds with HY if it succeeded, or HN if it failed.

====Final handshake====
After sending an H command, the calling system sends a final packet {{code|\20OOOOOO\0}} (control-P, six ohs, null-terminator) and the called system responds with {{code|\20OOOOOO\0}} (control-P, seven ohs, null-terminator). Some systems will simply hang up on the successful reception of the H command and not bother with the final handshake.

===g-protocol===
Within the suite of protocols in UUCP, the underlying g-protocol is responsible for transferring information in an error-free form. The protocol originated as a general-purpose system for packet delivery, and thus offers a number of features that are not used by the UUCP package as a whole. These include a secondary channel that can send command data interspersed with a file transfer, and the ability to renegotiate the packet and window sizes during transmission. These extra features may not be available in some implementations of the UUCP stack.<ref name=faq>{{cite web |url=http://www.math.utah.edu/docs/info/uucp_5.html |title=UUCP Internals Frequently Asked Questions |first=Ian Lance |last=Taylor |date=8 March 1996 |access-date=29 August 2020 |archive-date=6 November 2019 |archive-url=https://web.archive.org/web/20191106212355/http://www.math.utah.edu/docs/info/uucp_5.html |url-status=live }}</ref>

The packet format consisted of a 6-byte header and then between zero and 4096 bytes in the payload. The packet starts with a single \020 (control-P). This is followed by a single byte, known as "K", containing a value of 1 to 8 indicating a packet size from 32 to 4096 bytes, or a 9 indicating a control packet. Many systems only supported K=2, meaning 64 bytes. The next two bytes were a 16-bit checksum of the payload, not including the header. The next byte is the data type and finally, the last byte is the XOR of the header, allowing it to be checked separately from the payload.<ref name=faq/>

The control byte consists of three bit-fields in the format TTXXXYYY. TT is the packet type, 0 for control packets (which also requires K=9 to be valid), 1 for alternate data (not used in UUCP), 2 for data, and 3 indicates a short packet that re-defines the meaning of K. In a data packet, XXX is the packet number for this packet from 0 to 7, and YYY is the last that was received correctly. This provides up to 8 packets in a window. In a control packet, XXX indicates the command and YYY is used for various parameters. For instance, transfers are started by sending a short control packet with TT=0 (control), XXX=7 and YYY the number of packets in a window, then sending another packet with XXX=6 and YYY as the packet length (encoded as it would be in K) and then a third packet that is identical to the first but XXX=5.<ref name=faq/>

g-protocol uses a simple [[sliding window]] system to deal with potentially long latencies between endpoints. The protocol allows packets to size from 32 to 4096 8-bit bytes, and windows that include 1 to 7 packets. In theory, a system using 4k packets and 7 packet windows (4096x7) would offer performance matching or beating the best file-transfer protocols like [[ZMODEM]]. In practice, many early implementations only supported a single setting of 64x3. As a result, the g-protocol has an undeserved reputation for poor performance. Confusion over the packet and window sizes led to the G-protocol, differing only in that it always used 4096x3. Taylor UUCP did not support G, but did support any valid requested window or packet size, so remote systems starting G would work fine with Taylor's g, while two Taylor systems could negotiate even faster connections.<ref name=faq/>

[[Telebit]] modems used [[protocol spoofing]] to improve the performance of g-protocol transfers by noticing end-of-packet markers being sent to the remote system and immediately sending an {{code|ACK}} back to the local host, pretending that the remote system had already received the packet and decoded it correctly. This triggered the software stack on the local computer to send the next packet, so rapidly that the transfer became almost continuous. The data between the two modems was error-corrected using a proprietary protocol based on [[Microcom Networking Protocol|MNP]] that ran over Telebit's half-duplex connections much better than g-protocol would normally,<ref name=faq/> because in the common 64x3 case the remote system would be sending a constant stream of {{code|ACK}}s that would overflow the low-speed return channel. Combined with the modem's naturally higher data rates, up to 23&nbsp;kbps, they greatly improved overall throughput and generally performed about seven times the speed of a 2400 bit/s modem.<ref>{{cite web |url=http://www.umich.edu/~archive/mac/misc/documentation/telecomminfo.txt |title=What You Need To Know About Modems |first=Kenneth |last=Kirksey |date=25 December 1991 |quote=The actual throughput is around 14400 bps. |access-date=29 August 2020 |archive-date=24 October 2020 |archive-url=https://web.archive.org/web/20201024183419/http://www.umich.edu/~archive/mac/misc/documentation/telecomminfo.txt |url-status=live }}</ref> They were widely used on UUCP hosts as they could quickly pay for themselves in reduced long-distance charges.

===Other protocols===
UUCP implementations also include other transfer protocols for use over certain links.

'''f-protocol''' is designed to run over 7-bit error-corrected links. This was originally intended for use on [[X.25]] links, which were popular for a time in the 1980s. It does not packetize data, instead, the entire file is sent as a single long string followed by a whole-file checksum. The similar '''x-protocol''' appears to have seen little or no use. '''d-protocol''' was similar to x, but intended for use on [[Datakit]] networks that connected many of [[Bell Labs]] offices.<ref name=faq/>

'''t-protocol''' originated in the BSD versions of UUCP and like some similar ones, is designed to run over 8-bit error-free [[TCP/IP]] links. It has no error correction at all, and the protocol consists simply of breaking up command and file data into 512 or 1024-byte packets to easily fit within typical TCP frames.

'''e-protocol''' ("e" for Ethernet) was developed by Clem Cole at [[MASSCOMP]] and was widely released by Brian Redman in the later HoneyDanBer versions.  It was developed and released before the t-protocol, but the t-protocol was more commonly used because the BSD version of UUCP was the dominant implementation. The e-protocol differs from the t-protocol only in that commands are not packetized and are instead sent as normal strings, while files are padded to the nearest 20 bytes.<ref name=faq/><ref name=masscomp-uucpmgmt>{{Cite book | title=UUCP Management Guide, Rev C |first=Stephen |last=Talbot |date=February 1988  |series=User Manuals |number=M-UUCP-MG |publisher=Massachusetts Computer Corporation }}</ref>

==Mail routing==
[[File:UUCP Email Address .jpg|thumb | Business card with UUCP email address]]
The {{code|uucp}} and {{code|uuxqt}} capabilities could be used to send [[email]] between machines, with suitable mail user interfaces and delivery agent programs.  A simple UUCP mail address was formed from the adjacent machine name, an [[exclamation mark]] (often pronounced ''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''.<ref>{{cite mailing list |url=https://mailarchive.ietf.org/arch/msg/irtf-discuss/DWOvH0uMV29sBxZ6rcrZgrQC-ow/ |title=[Internet Policy] Why the World Must Resist Calls to Undermine the Internet |date=20 March 2022 |access-date=24 March 2022 |mailing-list=IETF-Discussion |first=Vint |last=Cerf |author-link=Vint Cerf}}</ref>

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'' would generally 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''. Publishing a full path would be pointless, because it would be different, depending on where the sender was. (e.g. Ann at one site may have to send via path ''gway!tcol!canty!uoh!bigsite!foovax!barbox!user'', whereas from somewhere else, Bill has to send via the path ''pdp10!router22!bigsite!foovax!barbox!user''). 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 path===
An email address of this form was known as a '''bang path'''.
Bang paths of eight to ten machines (or ''hops'') were not uncommon in 1981, and late-night dial-up UUCP links could 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 "[[Rewriting|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 registered in the [[domain name system]] (DNS) as a [[top-level domain]].  The uucp community administered itself and did not mesh well with the administration methods and regulations governing the DNS; .uucp works where it needs to{{where|date=January 2017}}; some hosts{{which|date=January 2017}} punt mail out of SMTP queue into uucp queues on gateway machines if a .uucp address is recognized on an incoming SMTP connection.{{citation needed|date=January 2017}}

[[Usenet]] traffic was originally transmitted over the UUCP protocol, typically over dialup modems. At each receiving node, each Usenet article's ''Path'' header line would have the current node's name prepended to the path, separated by "!".  For example, an article that came in from node ''utzoo'' to node ''decvax'' with ''Path: [[Henry Spencer|utzoo!henry]]'' would have that line change to ''Path: decvax!utzoo!henry'').  Usenet software would then send a copy of each article to every neighbor node which had been configured to receive the newsgroup(s) that the article had been posted to -- unless that neighbor was already in the ''Path'' line.  These paths were thus used to ensure that articles did not "loop" back to a node that already had them.

In general, like other [[Non-Internet email address|older e-mail address formats]], bang paths have now been superseded by the "[[Email address#Syntax|@ notation]]", even by sites still using UUCP.  A UUCP-only site can register a DNS domain name, and have the DNS server that handles that domain provide [[MX record]]s that cause Internet mail to that site to be delivered to a UUCP host on the Internet that can then deliver the mail to the UUCP site.

==UUCPNET and mapping<!--'UUCPNET' redirects here-->==
'''UUCPNET'''<!--boldface per WP:R#PLA--> 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 relay]]s 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 line|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.

==Remote commands==
''uux'' is remote command execution over UUCP. The uux command is used to execute a [[Command (computing)|command]] on a [[remote system]], or to execute a command on the local system using files from remote systems. The command is run by the {{code|uucico}} daemon, which handles remote execution requests as simply another kind of file to batch-send to the remote system whenever a next-hop node is available. The remote system will then execute the requested command and return the result, when the original system is available. Both of these transfers may be indirect, via multi-hop paths, with arbitrary windows of availability. Even when executing a command on an always-available neighbor, uux is not instant.

==Decline==
UUCP usage began to die out with the rise of [[Internet service provider]]s offering inexpensive [[Serial Line IP|SLIP]] and [[Point-to-Point Protocol|PPP]] services. The UUCP Mapping Project was formally shut down in late 2000.

The UUCP protocol has now mostly been replaced by the Internet TCP/IP based protocols [[Simple Mail Transfer Protocol|SMTP]] for mail and [[Network News Transfer Protocol|NNTP]] for Usenet news.

In July 2012, Dutch Internet provider [[XS4ALL]] closed down its UUCP service, claiming it was "probably one of the last providers in the world that still offered it"; it had only 13 users at that time (prior to its shut-down it had refused requests from new users for several years).<ref>{{cite web |first=Niels |last=Huijbregts |date=30 July 2012 |url=https://blog.xs4all.nl/2012/07/30/afscheid-van-uucp |title=XS4ALL Weblog: Afscheid van UUCP (Goodbye to UUCP) |publisher=[[XS4ALL]] |language=nl |archive-url=https://web.archive.org/web/20130731202722/https://blog.xs4all.nl/2012/07/30/afscheid-van-uucp/ |archive-date=31 July 2013|url-status=live}}</ref>

==Current uses and legacy==
One surviving feature of UUCP is the chat file format, largely inherited by the [[Expect]] software package.

UUCP was in use over special-purpose high cost links (e.g. marine satellite links) long after its disappearance elsewhere,<ref>{{cite web
|url=http://www.linuxjournal.com/article/1111
|title=Linux Goes To Sea
|access-date=2009-02-21
|author=Randolph Bentson
|date=August 1995
|archive-date=2008-02-26
|archive-url=https://web.archive.org/web/20080226063830/http://www.linuxjournal.com/article/1111
|url-status=live
}}</ref> and still remains in legacy use.{{citation needed|date=July 2014}} In addition to legacy use, in 2021 new and innovative UUCP uses are growing, especially for telecommunications in the [[high frequency|HF]] band, for example, for communities in the [[Amazon rainforest]] for email exchange and other uses. A patch to Ian's UUCP was contributed to UUCP Debian Linux package<ref>{{cite web
|url=https://metadata.ftp-master.debian.org/changelogs//main/u/uucp/uucp_1.07-27_changelog
|title=UUCP 1.07.27-changelog
|access-date=2021-01-10
|author=Rafael Diniz
|date=January 2021
|archive-date=2020-08-12
|archive-url=https://web.archive.org/web/20200812102840/http://metadata.ftp-master.debian.org/changelogs/main/u/uucp/uucp_1.07-27_changelog
|url-status=live
}}</ref> to adapt for the HERMES (High-Frequency Emergency and Rural Multimedia Exchange System) project, which provides UUCP HF connectivity.<ref>{{cite web
|url=https://www.rhizomatica.org/hermes/
|title=High-frequency Emergency and Rural Multimedia Exchange System
|access-date=2021-01-10
|author=Rafael Diniz
|date=January 2021}}</ref>

In the mid 2000s, UUCP over TCP/IP (often encrypted, using the [[Secure Shell|SSH]] protocol<ref name=UUCPssh/>) was proposed{{by whom|date=December 2015}} for use when a computer does not have any fixed [[IP addresses]] but is still willing to run a standard [[mail transfer agent]] (MTA) like [[Sendmail]] or [[Postfix (software)|Postfix]].

Bang-like paths are still in use within the [[Usenet]] network, though not for routing; they are used to record, in the header of a message, the nodes through which that message has passed, rather than to direct where it will go next.<ref>{{cite IETF|title=Netnews Article Format|rfc=5536|sectionname=Path|section=3.1.5|page=14-16|author1=K. Murchison|author2=C. Lindsey|author3=D. Kohn|date=November 2009|publisher=[[Internet Engineering Task Force|IETF]]}}</ref> "Bang path" is also used as an expression for any explicitly specified [[routing]] path between network hosts. That usage is not necessarily limited to UUCP, IP routing, email messaging, or Usenet.

The concept of [[delay-tolerant networking]] protocols was revisited in the early 2000s.<ref>{{Cite conference |chapter= A Delay-Tolerant Network Architecture for Challenged Internets |pages= 27–34 |author= Kevin Fall |title= Proceedings of the 2003 conference on Applications, technologies, architectures, and protocols for computer communications - SIGCOMM '03 |publisher= ACM [[SIGCOMM]] |date= August 2003 |conference= 2003 Conference on Applications, Technologies, Architectures, and Protocols for Computer Communications |doi= 10.1145/863955.863960 |isbn= 978-1-58113-735-4 |doi-access= free }}</ref> Similar techniques as those used by UUCP can apply to other networks that experience delay or significant disruption.

==See also==
* [[Routing]]
* [[Sitename]]
* [[Mesh networking]]
* [[Berknet]]
* [[BITNET]]
* [[FidoNet]]
* [[History of email]]
* [[History of the Internet]]

==References==
{{Reflist}}

==External links==
* ''Using & Managing UUCP''.  Ed Ravin, Tim O'Reilly, Dale Doughtery, and Grace Todino.  1996, O'Reilly & Associates, Inc. {{ISBN|1-56592-153-4}}
* [[Mary Ann Horton|Mark Horton]] (1986).  ''{{IETF RFC|976}}: UUCP Mail Interchange Format Standard''. [[Internet Engineering Task Force]] Requests for Comment.
* [http://www.airs.com/ian/uucp-doc/uucp.html Taylor UUCP Documentation] – useful information about UUCP in general and various uucp protocols.
* The UUCP Project: {{webarchive|url=https://web.archive.org/web/20140106180112/http://www.uucp.org/history/|title=History|date=January 6, 2014}}

{{E-mail clients}}
{{Authority control}}

{{DEFAULTSORT:Uucp}}
[[Category:Network file transfer protocols]]
[[Category:Network protocols]]
[[Category:Usenet]]
[[Category:Unix SUS2008 utilities]]
[[Category:File transfer software]]