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Squid (software)
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{{Short description|Caching and forwarding HTTP web proxy}} {{Use dmy dates|date=January 2020}} {{Infobox software | name = Squid | logo = Squid Now.png | logo caption = Squid project logo<ref>{{cite web |url=https://www.squid-cache.org/Artwork/ |title=Squid Project Logo |access-date=6 July 2014}}</ref> | logo alt = | logo size = 200px | developer = Duane Wessels, Henrik Nordström, Amos Jeffries, Alex Rousskov, Francesco Chemolli, Robert Collins, Guido Serassio and volunteers<ref name="Who looks after the Squid project?">{{cite web |url=https://www.squid-cache.org/Intro/who.html |title=Who looks after the Squid project?}}</ref> | released = {{Start date and age|1996|07}} | latest release version = {{wikidata|property|preferred|references|edit|Q841783|P348|P548=Q2804309}} | latest release date = {{wikidata|qualifier|preferred|single|Q841783|P348|P548=Q2804309|P577}} | latest preview version = {{wikidata|property|preferred|references|edit|Q841783|P348|P548=Q51930650}} | latest preview date = {{wikidata|qualifier|preferred|single|Q841783|P348|P548=Q51930650|P577}} | repo = {{URL|github.com/squid-cache/squid}} | programming language = [[C++]]<ref>{{Citation |title=squid-cache/squid |date=2022-07-27 |url=https://github.com/squid-cache/squid |publisher=Squid |access-date=2022-07-27}}</ref> | operating system = [[Berkeley Software Distribution|BSD]], [[Linux]], [[Unix]], [[Microsoft Windows|Windows]]<ref>{{cite web |url=https://wiki.squid-cache.org/BestOsForSquid |title=What is the Best OS for Squid?}}</ref> | genre = [[Proxy server]] | license = [[GNU General Public License|GPL]] 2.0 or later<ref name="Squid License">{{cite web |url=https://bazaar.launchpad.net/~squid/squid/trunk/view/head:/README |title=Squid License}}</ref> | website = {{URL|https://www.squid-cache.org}} }} [[File:LAMP software bundle.svg|thumb|300px|The [[LAMP (software bundle)|LAMP stack]] with Squid as web cache.]] '''Squid''' is a [[web cache|caching]] and forwarding HTTP [[web proxy]]. It has a wide variety of uses, including speeding up a [[web server]] by caching repeated requests, caching [[World Wide Web]] (WWW), [[Domain Name System]] (DNS), and other [[Computer network|network]] lookups for a group of people sharing network resources, and aiding security by filtering traffic. Although used for mainly [[HTTP]] and [[File Transfer Protocol]] (FTP), Squid includes limited support for several other [[protocol (computing)|protocols]] including [[Internet Gopher]], Secure Sockets Layer (SSL),<ref name=":0" /> [[Transport Layer Security]] (TLS), and Hypertext Transfer Protocol Secure ([[HTTPS]]). Squid does not support the [[SOCKS]] protocol, unlike [[Privoxy]], with which Squid can be used in order to provide SOCKS support. Squid was originally designed to run as a [[daemon (computer software)|daemon]] on [[Unix-like]] systems. A Windows port was maintained up to version 2.7. New versions available on Windows use the [[Cygwin]] environment.<ref>{{cite web|title=Squid for Windows |website=[[GitHub]] |url=https://github.com/diladele/squid-windows |quote=Current build is based on the latest Squid 4 build for Cygwin Windows 64 bit |date=February 2024}}</ref><ref>{{cite web|title=Squid-cache.org Knowledge Base |url=https://wiki.squid-cache.org/KnowledgeBase/Windows |quote=Squid on Windows }}</ref> Squid is [[free software]] released under the [[GNU General Public License]]. ==History== Squid was originally developed as the ''Harvest object cache'',<ref name=":0">C.Mic Bowman, Peter B. Danzig, Darren R. Hardy, Udi Manper, Michael F. Schwartz, The Harvest information discovery and access system, Computer Networks and ISDN Systems, Volume 28, Issues 1–2, December 1995, Pages 119–125. [https://dx.doi.org/10.1016/0169-7552(95)00098-5 doi:10.1016/0169-7552(95)00098-5]</ref> part of the [[Harvest project]] at the [[University of Colorado Boulder]].<ref>[http://www.squid-cache.org/Intro/ Squid intro], on the Squid website</ref><ref>[http://mail-archives.apache.org/mod_mbox/httpd-dev/199504.mbox/%3CPine.BSD.3.91.950404163551.11902J-100000@get.wired.com%3E ''Harvest cache now available as an "httpd accelerator"''], by Mike Schwartz on the http-wg mailing list, Tue, 4 April 1995, as forwarded by [[Brian Behlendorf]] to the [[Apache HTTP Server]] developers' mailing list</ref> Further work on the program was completed at the [[University of California, San Diego]] and funded via two grants from the [[National Science Foundation]].<ref>{{cite web|title=Squid Sponsors |url=http://www.squid-cache.org/SPONSORS.txt |archive-url=https://web.archive.org/web/20070511220833/http://www.squid-cache.org/SPONSORS.txt |archive-date=11 May 2007 |access-date=13 February 2007 |quote=The NSF was the primary funding source for Squid development from 1996–2000. Two grants (#NCR-9616602, #NCR-9521745) received through the Advanced Networking Infrastructure and Research (ANIR) Division were administered by the University of California San Diego}}</ref> Duane Wessels forked the "last pre-commercial version of Harvest" and renamed it to Squid to avoid confusion with the commercial fork called Cached 2.0, which became [[NetCache]].<ref name="auug-keynote">Duane Wessels [https://web.archive.org/web/20051030045131/http://www.life-gone-hazy.com/writings/auug-keynote.ps.gz Squid and ICP: Past, Present, and Future], Proceedings of the Australian Unix Users Group. September 1997, Brisbane, Australia</ref><ref>{{cite web |url=http://www.netcache.com/ |title=netcache.com |access-date=7 August 2012 |url-status=dead |archive-url=https://web.archive.org/web/19961112032719/http://www.netcache.com/ |archive-date=12 November 1996}}</ref> Squid version 1.0.0 was released in July 1996.<ref name="auug-keynote"/> [[SquidNT]], a port of the Squid proxy server was merged into the main Squid project in September 2006.<ref>{{cite web|title=Squid FAQ: Does Squid run on Windows? |url=https://wiki.squid-cache.org/SquidFaq/AboutSquid#head-500ddc367517c94cdf5cc49cb26868ab64becf63 }}</ref> Squid is now developed almost exclusively through volunteer efforts. In October 2023, it was revealed that Squid continued to suffer from 35 security vulnerabilities which had not been fixed for two and a half years after their initial reporting.<ref>{{cite web | url=https://joshua.hu/squid-security-audit-35-0days-45-exploits | title=55 Vulnerabilities in Squid Caching Proxy and 35 0days | date=11 October 2023 }}</ref> ==Basic functionality== After a Squid proxy server is installed, [[web browser]]s can be configured to use it as a [[Proxy server|proxy]] HTTP server, allowing Squid to retain copies of the documents returned, which, on repeated requests for the same documents, can reduce access time as well as [[Bandwidth (computing)|bandwidth]] consumption. This is often useful for [[Internet service provider]]s to increase speed to their customers, and [[local area network|LANs]] that share an [[Internet]] connection. Because the caching servers are controlled by the web service operator, caching proxies do not anonymize the user and should not be confused with anonymizing proxies. A client program (e.g. browser) either has to specify explicitly the proxy server it wants to use (typical for ISP customers), or it could be using a proxy without any extra configuration: "transparent caching", in which case all outgoing HTTP requests are intercepted by Squid and all responses are cached. The latter is typically a corporate set-up (all clients are on the same LAN) and often introduces the privacy concerns mentioned above. Squid has some features that can help [[Anonymity|anonymize]] connections, such as disabling or changing specific header fields in a [[client (computing)|client's]] HTTP requests. Whether these are set, and what they are set to do, is up to the person who controls the computer running Squid. People requesting pages through a network which transparently uses Squid may not know whether this information is being logged.<ref>See the documentation for {{mono|header_access}} and {{mono|header_replace}} for further details.</ref> Within UK organisations at least, users should be informed if computers or internet connections are being monitored.<ref>See, for example, [http://www.yourprivacy.co.uk/computer-monitoring-workplace-your-privacy.html Computer Monitoring In The Workplace and Your Privacy]</ref> ==Reverse proxy== The above setup, caching the contents of an unlimited number of [[webserver]]s for a limited number of clients, is the classical one. Another setup is "[[reverse proxy]]" or "webserver acceleration" (using {{mono|http_port 80 accel vhost}}). In this mode, the cache serves an unlimited number of clients for a limited number of—or just one—web servers. As an example, if ''slow.example.com'' is a "real" web server, and ''www.example.com'' is the Squid cache server that "accelerates" it, the first time any page is requested from ''www.example.com'', the cache server would get the actual page from ''slow.example.com'', but later requests would get the stored copy directly from the accelerator (for a configurable period, after which the stored copy would be discarded). The result, without any action by the clients, is less traffic to the source server, meaning less CPU and memory usage, and less need for bandwidth. This does, however, mean that the source server cannot accurately report on its traffic numbers without additional configuration, as all requests would seem to have come from the reverse proxy. A way to adapt the reporting on the source server is to use the [[X-Forwarded-For]] HTTP header reported by the reverse proxy, to get the real client's IP address. It is possible for one Squid server to serve simultaneously as a normal and a reverse proxy. For example, a business might host its own website on a web server, with a Squid server acting as a reverse proxy between clients (customers accessing the website from outside the business) and the web server. The same Squid server could act as a classical web cache, caching HTTP requests from clients within the business (i.e., employees accessing the internet from their workstations), so accelerating web access and reducing bandwidth demands. ==Media-range limits== For example, a feature of the HTTP protocol is to limit a request to the range of data in the resource being referenced. This feature is used extensively by video streaming websites such as [[YouTube]], so that if a user clicks to the middle of the video progress bar, the server can begin to send data from the middle of the file, rather than sending the entire file from the beginning and the user waiting for the preceding data to finish loading. Partial downloads are also extensively used by Microsoft [[Windows Update]] so that extremely large update packages can download in the background and pause halfway through the download, if the user turns off their computer or disconnects from the Internet. The [[Metalink]] download format enables clients to do segmented downloads by issuing partial requests and spreading these over a number of mirrors. Squid can relay partial requests to the origin web server. In order for a partial request to be satisfied at a fast speed from cache, Squid requires a full copy of the same object to already exist in its storage. If a proxy video user is watching a video stream and browses to a different page before the video completely downloads, Squid cannot keep the partial download for reuse and simply discards the data. Special configuration is required to force such downloads to continue and be cached.<ref>{{cite web |title=Squid Configuration Reference |url=http://www.squid-cache.org/Doc/config/quick_abort_min/ |access-date=26 November 2012}}</ref> ==Supported operating systems== Squid supports many [[operating system]]s, including: {{Div col|colwidth=22em}} * [[IBM AIX|AIX]] * [[BSD/OS|BSDI]] * [[Digital Unix]] * [[FreeBSD]] * [[FreeBSD jail]] * [[OpenWRT]] * [[Raspbian]] * [[Docker (software)]] * [[Ubuntu]] * [[pfSense]] * [[OPNsense]] * [[Kali Linux]] * [[CentOS]] * [[HP-UX]] * [[IRIX]] * [[Linux]] * [[Red Hat Enterprise Linux]] * [[SUSE Linux]] * [[Arch Linux]] * [[Linux Mint]] * [[Debian]] * [[webOS]] on Palm * [[macOS]] * [[NetBSD]] * [[NeXTStep]] * [[OpenBSD]] * [[OS/2]] (including [[ArcaOS]] and [[eComStation]])<ref name="SquidWarp">[http://os2ports.smedley.info/index.php?page=squid OS/2 Ports by Paul Smedley], OS/2 Ports</ref> * [[SCO OpenServer]] * [[Oracle Solaris|Solaris]] * [[UnixWare]] * [[Microsoft Azure]] also Microsoft Nano Server * [[Windows]]<ref>{{Cite web|url=https://wiki.squid-cache.org/KnowledgeBase/Windows|title=KnowledgeBase/Windows - Squid Web Proxy Wiki}}</ref> {{div col end}} ==See also== {{Portal|Free and open-source software}} * [[Web accelerator]] which discusses host-based HTTP acceleration * [[Proxy server]] which discusses client-side proxies * [[Reverse proxy]] which discusses origin-side proxies * [[Comparison of web servers]] * [[Web Cache Communication Protocol]] Cisco WCCP can also function with Squid * [[Riverbed Technology]] RiOS supports Squid * [[Junos OS]] JSA DSM for Squid Web Proxy records all cache and access log events. ==References== {{Reflist}} ==Further reading== * {{cite book |last=Wessels |first=Duane |year=2004 |title=Squid: The Definitive Guide |publisher=[[O'Reilly Media]] |isbn=978-0-596-00162-9}} * {{cite book |last=Saini |first=Kulbir |year=2011 |title=Squid Proxy Server 3.1: Beginner's Guide |publisher=[[Packt Publishing]] |isbn=978-1-849-51390-6}} ==External links== * {{Official website}} * [https://squidproxy.wordpress.com/ Squid Blog] * [https://web.archive.org/web/20100415153216/http://www.deckle.co.za/squid-users-guide/ Squid User's Guide] * [https://wiki.dd-wrt.com/wiki/index.php/Squid_Transparent_Proxy Squid Transparent Proxy For DD-WRT] * [https://www.webos-internals.org/wiki/SetupSquidTransparentProxy Palm WebOS Guide] - Squid install guide * [https://www.sweetnam.eu/index.php/Reverse_Proxy_with_Squid Squid reverse proxy] – Create a reverse proxy with Squid * [https://www.visolve.com/squid/ Configuration Manual] – ViSolve Squid Configuration Manual Guide * [http://www.squid-cache.org/Doc/config/ Configuration Manual] – Authoritative Squid Configuration Options * {{cite web |url=http://www.webmasterwords.com/squid-proxy-on-solaris |title=Solaris Setup |archive-url=https://web.archive.org/web/20080115182525/http://www.webmasterwords.com/squid-proxy-on-solaris |archive-date=15 January 2008}} – Setup squid on solaris * [https://linuxinpakistan.com/squid-installation-centos-fedora-red-hat SQUID – Installation on CentOS, Fedora and Red Hat] {{DEFAULTSORT:Squid (Software)}} [[Category:Free proxy servers]] [[Category:Reverse proxy]] [[Category:Proxy server software for Linux]] [[Category:Unix network-related software]] [[Category:Gopher clients]] [[Category:Cross-platform free software]]
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