fork (software development)

The word "fork" has been used to mean "to divide in branches, go separate ways" as early as the 14th century.[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 }} In the software environment, the word evokes the fork system call, which causes a running process to split itself into two (almost) identical copies that (typically) diverge to perform different tasks."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|access-date=20 October 2012|url-status=live|archive-url=https://web.archive.org/web/20131202221721/http://flosshub.org/sites/flosshub.org/files/paper_0.pdf|archive-date=2 December 2013|doi=10.1007/978-3-642-33442-9_1|doi-access=free}}

In the context of software development, "fork" was used in the sense of creating a revision control "branch" by Eric Allman as early as 1980, in the context of Source Code Control System: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.

{{quotation|Creating a branch "forks off" a version of the program.}}

The term was in use on Usenet by 1983 for the process of creating a subgroup to move topics of discussion to.[https://groups.google.com/group/net.misc/browse_thread/thread/b0e9f8531558b7e9/1cc726d9e9e05ebd?q=fork#1cc726d9e9e05ebd Can somebody fork off a "net.philosophy"?] (John Gilmore, net.misc, 18 January 1983)

"Fork" is not known to have been used in the sense of a community schism during the origins of Lucid Emacs (now XEmacs) (1991) or the Berkeley Software Distributions (BSDs) (1993–1994); Russ Nelson used the term "shattering" for this sort of fork in 1993, attributing it to John Gilmore.[https://groups.google.com/group/gnu.misc.discuss/browse_thread/thread/1bba70b8f8676c43/309504a5a51dd0f0 Shattering — good or bad?] (Russell Nelson, gnu.misc.discuss, 1 October 1993) However, "fork" was in use in the present sense by 1995 to describe the XEmacs split,[https://groups.google.com/group/cu.cs.macl.info/browse_thread/thread/ed9e5ff9cb21c359/4ce930d2fd1271eb?q=%22fork+of%22+xemacs#4ce930d2fd1271eb Re: Hey Franz: 32K Windows SUCK!!!!!] (Bill Dubuque, cu.cs.macl.info, 21 September 1995) and was an understood usage in the GNU Project by 1996.[https://groups.google.com/group/gnu.misc.discuss/browse_thread/thread/5d7529d865d4d9ca/69ebc4771f32bc45?q=fork+xemacs&utoken=jCqifzMAAABlYGNE0Z8-NzB8d_a6gkmMuNtzuV4zLfLK8bEgnt4z8g27cB9GA0FI9e6hHUM__C_J8dUPGZeQNP0WkVA49NN0 Lignux?] (Marcus G. Daniels, gnu.misc.discuss, 7 June 1996)

Free and open-source software may be legally forked without prior approval of those currently developing, managing, or distributing the software per both The Free Software Definition and The Open Source Definition:

{{quotation|The freedom to distribute copies of your modified versions to others (freedom 3). By doing this, you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.|The Free Software Definition{{cite web

|url = https://www.gnu.org/philosophy/free-sw.html

|title = The Free Software Definition

|first = Richard

|last = Stallman

|publisher = Free Software Foundation

|access-date = 2013-10-15

|url-status = live

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

|archive-date = 14 October 2013

}}}}

{{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{{cite web|url=http://opensource.org/docs/osd|title=The Open Source Definition|date=7 July 2006 |publisher=The Open Source Initiative|access-date=15 October 2013|url-status=live|archive-url=https://web.archive.org/web/20131015144021/http://opensource.org/docs/osd|archive-date=15 October 2013}}}}

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. 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,{{cite web |last=Raymond |first=Eric S. |author-link=Eric S. Raymond |date=15 August 2002 |title=Promiscuous Theory, Puritan Practice |url=http://www.catb.org/~esr/writings/cathedral-bazaar/homesteading/ar01s03.html |url-status=live |archive-url=https://web.archive.org/web/20061006010031/http://www.catb.org/~esr/writings/cathedral-bazaar/homesteading/ar01s03.html |archive-date=6 October 2006 |website=catb.org}} 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:[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 August 2000)

{{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/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.}}

David A. Wheeler notes[http://www.dwheeler.com/oss_fs_why.html#forking Why Open Source Software / Free Software (OSS/FS, FLOSS, or FOSS)? Look at the Numbers!: Forking] {{webarchive|url=https://web.archive.org/web/20060405112628/http://www.dwheeler.com/oss_fs_why.html |date=5 April 2006 }} (David A. Wheeler) four possible outcomes of a fork, with examples:

1. The death of the fork. This is by far the most common case. It is easy to declare a fork, but considerable effort to continue independent development and support.
2. A re-merging of the fork (e.g., egcs becoming "blessed" as the new version of GNU Compiler Collection.)
3. The death of the original (e.g. the X.Org Server succeeding and XFree86 dying.)
4. 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".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|access-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|archive-url=https://web.archive.org/web/20150421055059/http://lwn.net/Articles/628527/|archive-date=21 April 2015}} See also {{cite thesis|type=PhD|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}} With a DVCS such as Mercurial or 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 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 numbers typically used for initial versions of programs like 0.0.1, 0.1, or 1.0 even if the original software was at another version such as 3.0, 4.0, or 5.0. An exception is sometimes made when the forked software is designed to be a drop-in replacement for the original project, e.g. MariaDB for MySQL[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 }} or LibreOffice for OpenOffice.org.

The BSD licenses permit forks to become proprietary software, and copyleft proponents say that commercial incentives thus make proprietisation almost inevitable. (Copyleft licenses can, however, be circumvented via dual-licensing with a proprietary grant in the form of a Contributor License Agreement.) Examples include macOS (based on the proprietary NeXTSTEP and the open source FreeBSD), Cedega and CrossOver (proprietary forks of Wine, though CrossOver tracks Wine and contributes considerably), EnterpriseDB (a fork of PostgreSQL, adding Oracle compatibility features[http://www.enterprisedb.com EnterpriseDB] {{webarchive|url=https://web.archive.org/web/20061113052033/http://www.enterprisedb.com/ |date=13 November 2006 }}), Supported PostgreSQL with their proprietary ESM storage system,[http://www.fastware.com.au/docs/FujitsuSupportedPostreSQLWhitePaperV1_02.pdf Fujitsu Supported PostgreSQL] {{webarchive|url=https://web.archive.org/web/20060820144738/http://fastware.com.au/docs/FujitsuSupportedPostreSQLWhitePaperV1_02.pdf |date=20 August 2006 }} and Netezza's[http://www.netezza.com/media/2004/Weblog.htm Netezza] {{webarchive|url=https://web.archive.org/web/20061113210650/http://www.netezza.com/media/2004/Weblog.htm |date=13 November 2006 }} proprietary highly scalable derivative of PostgreSQL. Some of these vendors contribute back changes to the community project, while some keep their changes as their own competitive advantages.

In proprietary software, the copyright is usually held by the employing entity, not by the individual software developers. Proprietary code is thus more commonly forked when the owner needs to develop two or more versions, such as a windowed version and a command line version, or versions for differing operating systems, such as a word processor for IBM PC compatible machines and Macintosh computers. Generally, such internal forks will concentrate on having the same look, feel, data format, and behavior between platforms so that a user familiar with one can also be productive or share documents generated on the other. This is almost always an economic decision to generate a greater market share and thus pay back the associated extra development costs created by the fork.

A notable proprietary fork not of this kind is the many varieties of proprietary Unix—almost all derived from AT&T Unix under license and all called "Unix", but increasingly mutually incompatible.[http://linuxmafia.com/faq/Licensing_and_Law/forking.html Fear of forking] {{webarchive|url=https://web.archive.org/web/20121217044712/http://linuxmafia.com/faq/Licensing_and_Law/forking.html |date=17 December 2012 }} – An essay about forking in free software projects, by Rick Moen See Unix wars.

• List of software forks
• Source port
• Downstream (software development)
• Group decision-making
• Modular programming
• Modding
• Custom software
• Personalization
• Team effectiveness
• Duplicate code
• ROM Hacking

{{Reflist}}

• [http://meatballwiki.org/wiki/RightToFork Right to Fork] at Meatball Wiki
• A PhD examining forking: [http://helda.helsinki.fi/handle/10138/153135 (Nyman, 2015)] {{Webarchive|url=https://web.archive.org/web/20230716095029/http://helda.helsinki.fi/handle/10138/153135 |date=16 July 2023 }} "Understanding Code Forking in Open Source Software – An examination of code forking, its effect on open source software, and how it is viewed and practiced by developers"

{{FOSS}}

{{Version control software}}

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Category:Software project management