Fork (software development): Difference between revisions

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== Etymology ==

The word "fork" has been used to mean "to divide in branches, go separate ways" as early as the 14th century.<ref>[http://www.etymonline.com/index.php?term=fork Entry 'fork' in Online Etymology Dictionary] {{webarchive|url=https://web.archive.org/web/20120525165727/http://www.etymonline.com/index.php?term=fork |date=25 May 2012 }}</ref> In the software environment, the word evokes the [[Fork (system call)|fork]] system call, which causes a running process to split itself into two (almost) identical copies that (typically) diverge to perform different tasks.<ref>"The term fork is derived from the POSIX standard for operating systems: the system call used so that a process generates a copy of itself is called fork()." {{cite conference|url=http://flosshub.org/sites/flosshub.org/files/paper_0.pdf|title=A Comprehensive Study of Software Forks: Dates, Reasons and Outcomes|first1=Gregorio|last1=Robles|first2=Jesús M.|last2=González-Barahona|conference=OSS 2012 The Eighth International Conference on Open Source Systems|year=2012|accessdateaccess-date=20 Oct 2012|url-status=live|archiveurlarchive-url=https://web.archive.org/web/20131202221721/http://flosshub.org/sites/flosshub.org/files/paper_0.pdf|archivedatearchive-date=2 December 2013|df=dmy-all|doi=10.1007/978-3-642-33442-9_1}}</ref>

In the context of software development, "fork" was used in the sense of creating a revision control "[[branching (revision control)|branch]]" by [[Eric Allman]] as early as 1980, in the context of [[Source Code Control System|SCCS]]:<ref>Allman, Eric. [http://sccs.sourceforge.net/man/sccs.me.html "An Introduction to the Source Code Control System."] {{webarchive|url=https://web.archive.org/web/20141106144859/http://sccs.sourceforge.net/man/sccs.me.html |date=6 November 2014 }} Project Ingres, University of California at Berkeley, 1980.</ref>

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|last = Stallman

|publisher = Free Software Foundation

|accessdateaccess-date = 2013-10-15

|url-status = live

|archiveurlarchive-url = https://web.archive.org/web/20131014132149/http://www.gnu.org/philosophy/free-sw.html

|archivedatearchive-date = 14 October 2013

|df = dmy-all

}}</ref>}}

{{quotation|3. Derived Works: The license must allow modifications and derived works, and must allow them to be distributed under the same terms as the license of the original software.|[[The Open Source Definition]]<ref>{{cite web|url=http://opensource.org/docs/osd|title=The Open Source Definition|publisher=The Open Source Initiative|accessdateaccess-date=15 October 2013|url-status=live|archiveurlarchive-url=https://web.archive.org/web/20131015144021/http://opensource.org/docs/osd|archivedatearchive-date=15 October 2013|df=dmy-all}}</ref>}}

In free software, forks often result from a schism over different goals or personality clashes. In a fork, both parties assume nearly identical code bases, but typically only the larger group, or whoever controls the Web site, will retain the full original name and the associated user community. Thus, there is a reputation penalty associated with forking.<ref name=wheeler/> The relationship between the different teams can be cordial or very bitter. On the other hand, a ''friendly fork'' or a ''soft fork'' is a fork that does not intend to compete, but wants to eventually merge with the original.

[[Eric S. Raymond]], in his essay ''[[Homesteading the Noosphere]]'',<ref>{{cite web|url=http://www.catb.org/~esr/writings/cathedral-bazaar/homesteading/ar01s03.html|title=Promiscuous Theory, Puritan Practice|date=15 August 2002|authorlinkauthor-link=Eric S. Raymond|first=Eric S.|last=Raymond|url-status=live|archiveurlarchive-url=https://web.archive.org/web/20061006010031/http://www.catb.org/~esr/writings/cathedral-bazaar/homesteading/ar01s03.html|archivedatearchive-date=6 October 2006|df=dmy-all}}</ref> stated that "The most important characteristic of a fork is that it spawns competing projects that cannot later exchange code, splitting the potential developer community". He notes in the [[Jargon File]]:<ref>[http://catb.org/jargon/html/F/forked.html Forked] {{webarchive|url=https://web.archive.org/web/20111108171515/http://catb.org/jargon/html/F/forked.html |date=8 November 2011 }} ([[Jargon File]]), first added to [http://magic-cookie.co.uk/jargon/jarg422/ v4.2.2] {{webarchive|url=https://web.archive.org/web/20120114192615/http://magic-cookie.co.uk/jargon/jarg422/ |date=14 January 2012 }}, 20 Aug 2000)</ref>

{{quotation|Forking is considered a Bad Thing—not merely because it implies a lot of wasted effort in the future, but because forks tend to be accompanied by a great deal of strife and acrimony between the successor groups over issues of legitimacy, succession, and design direction. There is serious social pressure against forking. As a result, major forks (such as the [[GNU Emacs|Gnu-Emacs]]/[[XEmacs]] split, the fissioning of the [[386BSD]] group into three daughter projects, and the short-lived GCC/EGCS split) are rare enough that they are remembered individually in hacker folklore.}}

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# Successful branching, typically with differentiation (''e.g.'', [[OpenBSD]] and [[NetBSD]].)

[[Distributed revision control]] (DVCS) tools have popularised a less emotive use of the term "fork", blurring the distinction with "branch".<ref>''e.g.'' {{cite web|url=https://lwn.net/Articles/628527/|title=An "open governance" fork of Node.js|first=Nathan|last=Willis|work=LWN.net|date=15 January 2015|accessdateaccess-date=15 January 2015|quote=Forks are a natural part of the open development model—so much so that GitHub famously plasters a "fork your own copy" button on almost every page.|url-status=live|archiveurlarchive-url=https://web.archive.org/web/20150421055059/http://lwn.net/Articles/628527/|archivedatearchive-date=21 April 2015|df=dmy-all}} See also {{cite thesis|type=Ph.D.|page=57|first=Linus|last=Nyman|title=Understanding Code Forking in Open Source Software|publisher=Hanken School of Economics|year=2015|quote=Where practitioners have previously had rather narrow definitions of a fork, [...] the term now appears to be used much more broadly. Actions that would traditionally have been called a branch, a new distribution, code fragmentation, a pseudo-fork, etc. may all now be called forks by some developers. This appears to be in no insignificant part due to the broad definition and use of the term fork by GitHub.|hdl=10138/153135}}</ref> With a DVCS such as [[Mercurial]] or [[Git (software)|Git]], the normal way to contribute to a project, is to first create a personal branch of the repository, independent of the main repository, and later seek to have your changes integrated with it. Sites such as [[GitHub]], [[Bitbucket]] and [[Launchpad (website)|Launchpad]] provide free DVCS hosting expressly supporting independent branches, such that the technical, social and financial barriers to forking a source code repository are massively reduced, and GitHub uses "fork" as its term for this method of contribution to a project.

Forks often restart version numbering from 0.1 or 1.0 even if the original software was at version 3.0, 4.0, or 5.0. An exception is when the forked software is designed to be a drop-in replacement for the original project, ''e.g.'' [[MariaDB]] for [[MySQL]]<ref>[http://programmers.stackexchange.com/questions/31551/forked-a-project-where-do-my-version-numbers-start Forked a project, where do my version numbers start?] {{webarchive|url=https://web.archive.org/web/20110826152252/http://programmers.stackexchange.com/questions/31551/forked-a-project-where-do-my-version-numbers-start |date=26 August 2011 }}</ref> or [[LibreOffice]] for [[OpenOffice.org]].