UUCP
AT&T Bell Laboratories | |
---|---|
Initial release | 1979 |
Operating system | Unix and Unix-like, DOS, OS/2, OpenVMS, AmigaOS, classic Mac OS, CP/M |
Type | Command |
UUCP (Unix-to-Unix Copy)
A command named 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
(the communication program that performs the file transfers), uustat
(reports statistics on recent activity), uuxqt
(execute commands sent from remote machines), and uuname
(reports the UUCP name of the local system). Some versions of the suite include uuencode
/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,[2] classic Mac OS, and even CP/M.
History
UUCP was originally written at
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.[5][6]
The original UUCP was 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").[7]
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.[8] Taylor UUCP was released under the GNU General Public License. Taylor UUCP addressed security holes which allowed some of the original network worms 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-
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]
Technology
Before the widespread availability of
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.
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 TCP/IP.[9][10] 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 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, \20Shere=hostname\0
, where \20 is the control-P character, and \0 is a trailing null. The caller's UUCP responds with \20Scallername options\0
, 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 RYou are unknown to me\0
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 reason. 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 \20OOOOOO\0
(control-P, six ohs, null-terminator) and the called system responds with \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.[11]
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.[11]
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.[11]
g-protocol uses a simple
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 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 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 MNP that ran over Telebit's half-duplex connections much better than g-protocol would normally,[11] because in the common 64x3 case the remote system would be sending a constant stream of ACK
s that would overflow the low-speed return channel. Combined with the modem's naturally higher data rates, they greatly improved overall throughput and generally performed about seven times the speed of a 2400 bit/s modem.[12] 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.[11]
t-protocol originated in the BSD versions of UUCP and like some similar ones, is designed to run over 8-bit error-free
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.[11][13]
Mail routing
The uucp
and 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.[14]
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 "rewrite" the path, sending mail via "faster" routes—this practice tended to be frowned upon.
The "pseudo-domain" ending
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, like other older e-mail address formats, bang paths have now been superseded by the "@ 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 records 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 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
Connections with the Internet
Many UUCP hosts, particularly those at universities, were also connected to the
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
Remote commands
uux is remote command execution over UUCP. The uux command is used to execute a
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
The UUCP protocol has now mostly been replaced by the Internet TCP/IP based protocols SMTP for mail and 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).[15]
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,[16] and still remains in legacy use.[citation needed] In addition to legacy use, in 2021 new and innovative UUCP uses are growing, especially for telecommunications in the 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[17] to adapt for the HERMES (High-Frequency Emergency and Rural Multimedia Exchange System) project, which provides UUCP HF connectivity.[18]
In the mid 2000s, UUCP over TCP/IP (often encrypted, using the
.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.[19] "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.[20] Similar techniques as those used by UUCP can apply to other networks that experience delay or significant disruption.
See also
References
- ^ UNIX(TM) TIME-SHARING SYSTEM: UNIX PROGRAMMER'S MANUAL, Seventh Edition, Volume 1 (PDF). Murray Hill, New Jersey: Bell Telephone Laboratories, Incorporated. January 1979. Archived (PDF) from the original on 2016-04-29. Retrieved 2018-02-20.
- ^ "Aminet - Search".
- McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. 139. Archived(PDF) from the original on 2017-11-11. Retrieved 2015-02-01.
- ^ "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" (PDF). Archived (PDF) from the original on 2018-02-21. Retrieved 2018-02-21.
- ^ Houlder, Peter (19 January 2007). "Starting the Commercial Internet in the UK" (PDF). 6th UK Network Operators' Forum. Retrieved 2020-02-12.
- ^ Reid, Jim (3 April 2007). "Networking in UK Academia ~25 Years Ago" (PDF). 7th UK Network Operators' Forum. Retrieved 2020-02-12.
- ^ Gary J. Murakami (September 24, 1988). "The History of ihnp4 and The Growth of the Email Network". Archived from the original on September 11, 2013. Retrieved June 7, 2013.
- ^ Ian Lance Taylor (September 1991). "Beta release of new UUCP package available". Retrieved 2009-01-19.
- ^ Ian Lance Taylor (June 2003). "UUCP 'f' Protocol". Archived from the original on 2008-07-18. Retrieved 2008-08-04.
- ^ a b Fabien Penso. "UUCPssh". Archived from the original on 2009-09-30. Retrieved 2009-08-09.
- ^ a b c d e f g Taylor, Ian Lance (8 March 1996). "UUCP Internals Frequently Asked Questions". Archived from the original on 6 November 2019. Retrieved 29 August 2020.
- ^ Kirksey, Kenneth (25 December 1991). "What You Need To Know About Modems". Archived from the original on 24 October 2020. Retrieved 29 August 2020.
The actual throughput is around 14400 bps.
- ^ Talbot, Stephen (February 1988). UUCP Management Guide, Rev C. User Manuals. Massachusetts Computer Corporation.
- ^ Cerf, Vint (20 March 2022). "[Internet Policy] Why the World Must Resist Calls to Undermine the Internet". IETF-Discussion (Mailing list). Retrieved 24 March 2022.
- ^ Huijbregts, Niels (30 July 2012). "XS4ALL Weblog: Afscheid van UUCP (Goodbye to UUCP)" (in Dutch). XS4ALL. Archived from the original on 31 July 2013.
- ^ Randolph Bentson (August 1995). "Linux Goes To Sea". Archived from the original on 2008-02-26. Retrieved 2009-02-21.
- ^ Rafael Diniz (January 2021). "UUCP 1.07.27-changelog". Archived from the original on 2020-08-12. Retrieved 2021-01-10.
- ^ Rafael Diniz (January 2021). "High-frequency Emergency and Rural Multimedia Exchange System". Retrieved 2021-01-10.
- .
- ISBN 978-1-58113-735-4.
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
- RFC 976: UUCP Mail Interchange Format Standard. Internet Engineering Task ForceRequests for Comment.
- Taylor UUCP Documentation – useful information about UUCP in general and various uucp protocols.
- The UUCP Project: History at the Wayback Machine (archived January 6, 2014)