fork (software engineering)
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In
software engineering Software engineering is a systematic engineering approach to software development. A software engineer is a person who applies the principles of software engineering to design, develop, maintain, test, and evaluate computer software. The term '' ...
, a project fork happens when developers take a copy of
source code In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the w ...
from one software package and start independent development on it, creating a distinct and separate piece of software. The term often implies not merely a development branch, but also a split in the developer community; as such, it is a form of schism. Grounds for forking are varying user preferences and stagnated or discontinued development of the original software. Free and open-source software is that which, by definition, may be forked from the original development team without prior permission, and without violating
copyright A copyright is a type of intellectual property that gives its owner the exclusive right to copy, distribute, adapt, display, and perform a creative work, usually for a limited time. The creative work may be in a literary, artistic, educatio ...
law. However, licensed forks of proprietary software (''e.g.''
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...
) also happen.


Etymology

The word "fork" has been used to mean "to divide in branches, go separate ways" as early as the 14th century. In the software environment, the word evokes the
fork In cutlery or kitchenware, a fork (from la, furca 'pitchfork') is a utensil, now usually made of metal, whose long handle terminates in a head that branches into several narrow and often slightly curved tine (structural), tines with which one ...
system call, which causes a running process to split itself into two (almost) identical copies that (typically) diverge to perform different tasks. In the context of software development, "fork" was used in the sense of creating a revision control "
branch A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term ''twig'' usually ...
" by
Eric Allman Eric Paul Allman (born September 2, 1955) is an American computer programmer who developed sendmail and its precursor delivermail in the late 1970s and early 1980s at UC Berkeley. In 1998, Allman and Greg Olson co-founded the company Sendmail, I ...
as early as 1980, in the context of SCCS: The term was in use on
Usenet Usenet () is a worldwide distributed discussion system available on computers. It was developed from the general-purpose Unix-to-Unix Copy (UUCP) dial-up network architecture. Tom Truscott and Jim Ellis conceived the idea in 1979, and it wa ...
by 1983 for the process of creating a subgroup to move topics of discussion to. "Fork" is not known to have been used in the sense of a community schism during the origins of Lucid Emacs (now
XEmacs XEmacs is a graphical- and console-based text editor which runs on almost any Unix-like operating system as well as Microsoft Windows. XEmacs is a fork, based on a version of GNU Emacs from the late 1980s. Any user can download, use, and modify X ...
) (1991) or the
BSDs There are a number of Unix-like operating systems under active development, descended from the Berkeley Software Distribution (BSD) series of UNIX variants developed (originally by Bill Joy) at the University of California, Berkeley Electrical Eng ...
(1993–1994);
Russ Nelson Russell Nelson (born March 21, 1958) is an American computer programmer. He was a founding board member of the Open Source Initiative and briefly served as its president in 2005. Career Nelson wrote code for some programs: In 1983, he co-wrote ...
used the term "shattering" for this sort of fork in 1993, attributing it to
John Gilmore John Gilmore may refer to: * John Gilmore (activist) (born 1955), co-founder of the Electronic Frontier Foundation and Cygnus Solutions * John Gilmore (musician) (1931–1995), American jazz saxophonist * John Gilmore (representative) (1780–1845 ...
. However, "fork" was in use in the present sense by 1995 to describe the XEmacs split, and was an understood usage in the
GNU GNU () is an extensive collection of free software (383 packages as of January 2022), which can be used as an operating system or can be used in parts with other operating systems. The use of the completed GNU tools led to the family of operat ...
Project by 1996.


Forking of free and open-source software

Free and
open-source software Open-source software (OSS) is computer software that is released under a license in which the copyright holder grants users the rights to use, study, change, and distribute the software and its source code to anyone and for any purpose. Op ...
may be legally forked without prior approval of those currently developing, managing, or distributing the software per both
The Free Software Definition The Free Software Definition written by Richard Stallman and published by the Free Software Foundation (FSF), defines free software as being software that ensures that the end users have freedom in using, studying, sharing and modifying that softwa ...
and
The Open Source Definition ''The Open Source Definition'' is a document published by the Open Source Initiative, to determine whether a software license can be labeled with the open-source certification mark. The definition was taken from the exact text of the Debian Free ...
: 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'', 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: David A. Wheeler notesWhy Open Source Software / Free Software (OSS/FS, FLOSS, or FOSS)? Look at the Numbers!: Forking
(David A. Wheeler)
four possible outcomes of a fork, with examples: # 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. # A re-merging of the fork (''e.g.'', egcs becoming "blessed" as the new version of gcc.) # The death of the original (''e.g.'' the
X.Org Server X.Org Server is the free and open-source implementation of the X Window System display server stewarded by the X.Org Foundation. Implementations of the client-side X Window System protocol exist in the form of ''X11 libraries'', which serve a ...
succeeding and
XFree86 XFree86 is an implementation of the X Window System. It was originally written for Unix-like operating systems on IBM PC compatibles and was available for many other operating systems and platforms. It is free and open source software under the X ...
dying.) # Successful branching, typically with differentiation (''e.g.'', OpenBSD and NetBSD.)
Distributed revision control In software development, distributed version control (also known as distributed revision control) is a form of version control in which the complete codebase, including its full history, is mirrored on every developer's computer. Compared to centr ...
(DVCS) tools have popularised a less emotive use of the term "fork", blurring the distinction with "branch". With a DVCS such as
Mercurial Mercurial is a distributed revision control tool for software developers. It is supported on Microsoft Windows and Unix-like systems, such as FreeBSD, macOS, and Linux. Mercurial's major design goals include high performance and scalability, d ...
or
Git Git () is a distributed version control system: tracking changes in any set of files, usually used for coordinating work among programmers collaboratively developing source code during software development. Its goals include speed, data in ...
, 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 GitHub, Inc. () is an Internet hosting service for software development and version control using Git. It provides the distributed version control of Git plus access control, bug tracking, software feature requests, task management, continu ...
,
Bitbucket Bitbucket is a Git-based source code repository hosting service owned by Atlassian. Bitbucket offers both commercial plans and free accounts with an unlimited number of private repositories. Services Bitbucket Cloud Bitbucket Cloud (previ ...
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 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 MariaDB is a community-developed, commercially supported fork of the MySQL relational database management system (RDBMS), intended to remain free and open-source software under the GNU General Public License. Development is led by some of the ori ...
for
MySQL MySQL () is an open-source relational database management system (RDBMS). Its name is a combination of "My", the name of co-founder Michael Widenius's daughter My, and "SQL", the acronym for Structured Query Language. A relational database ...
or
LibreOffice LibreOffice () is a free and open-source office productivity software suite, a project of The Document Foundation (TDF). It was forked in 2010 from OpenOffice.org, an open-sourced version of the earlier StarOffice. The LibreOffice suite co ...
for
OpenOffice.org OpenOffice.org (OOo), commonly known as OpenOffice, is a discontinued open-source office suite. Active successor projects include LibreOffice (the most actively developed), Apache OpenOffice, Collabora Online (enterprise ready LibreOffice) a ...
. The BSD licenses permit forks to become proprietary software, and
copyleft Copyleft is the legal technique of granting certain freedoms over copies of copyrighted works with the requirement that the same rights be preserved in derivative works. In this sense, ''freedoms'' refers to the use of the work for any purpose ...
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 macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...
(based on the proprietary
NeXTSTEP NeXTSTEP is a discontinued object-oriented, multitasking operating system based on the Mach kernel and the UNIX-derived BSD. It was developed by NeXT Computer in the late 1980s and early 1990s and was initially used for its range of propri ...
and the open source FreeBSD), Cedega and
CrossOver Crossover may refer to: Entertainment Albums and songs * ''Cross Over'' (Dan Peek album) * ''Crossover'' (Dirty Rotten Imbeciles album), 1987 * ''Crossover'' (Intrigue album) * ''Crossover'' (Hitomi Shimatani album) * ''Crossover'' (Yoshino ...
(proprietary forks of
Wine Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...
, though CrossOver tracks Wine and contributes considerably), EnterpriseDB (a fork of PostgreSQL, adding Oracle compatibility features), Supported PostgreSQL with their proprietary ESM storage system, and Netezza'sNetezza
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.


Forking proprietary software

In
proprietary software Proprietary software is software that is deemed within the free and open-source software to be non-free because its creator, publisher, or other rightsholder or rightsholder partner exercises a legal monopoly afforded by modern copyright and i ...
, 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 A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
version, or versions for differing operating systems, such as a
word processor A word processor (WP) is a device or computer program that provides for input, editing, formatting, and output of text, often with some additional features. Early word processors were stand-alone devices dedicated to the function, but current ...
for IBM PC compatible machines and
Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and software en ...
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 Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...
—almost all derived from AT&T Unix under license and all called "Unix", but increasingly mutually incompatible.Fear of forking
– An essay about forking in
free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, no ...
projects, by Rick Moen
''See''
UNIX wars The Unix wars were struggles between vendors to set a standard for the Unix operating system in the late 1980s and early 1990s. Origins Although AT&T Corporation created Unix, by the 1980s, the University of California, Berkeley Computer Syste ...
.


See also

* List of software forks *
Source port A source port is a software project based on the source code of a game engine that allows the game to be played on operating systems or computing platforms with which the game was not originally compatible. Description Source ports are often c ...
*
Downstream (software development) In software development, downstream refers to a direction away from the original authors or maintainers of software that is distributed as source code, and is a qualification of a patch. For example, a patch ''sent downstream'' is offered to t ...
*
Group decision-making Group decision-making (also known as collaborative decision-making or collective decision-making) is a situation faced when individuals collectively make a choice from the alternatives before them. The decision is then no longer attributable to an ...
*
Modular programming Modular programming is a software design technique that emphasizes separating the functionality of a Computer program, program into independent, interchangeable modules, such that each contains everything necessary to execute only one aspect of th ...
**
Modding ''Modding'' is a slang expression derived from the English verb " to modify". The term refers to modification of hardware, software, or anything else, to perform a function not originally intended by the designer, or to achieve bespoke specif ...
*
Custom software Customised software (also known as bespoke software or tailor-made software) is software that is specially developed for some specific organization or other user. As such, it can be contrasted with the use of software packages developed for the ...
*
Personalization Personalization (broadly known as customization) consists of tailoring a service or a product to accommodate specific individuals, sometimes tied to groups or segments of individuals. A wide variety of organizations use personalization to improv ...
* Team effectiveness **
Duplicate code In computer programming, duplicate code is a sequence of source code that occurs more than once, either within a program or across different programs owned or maintained by the same entity. Duplicate code is generally considered undesirable for a n ...
*
ROM Hacking ROM hacking is the process of modifying a ROM image or ROM file of a video game to alter the game's graphics, dialogue, levels, gameplay, and/or other elements. This is usually done by technically inclined video game fans to improve an old game ...


References


External links


Right to Fork
at Meatball Wiki * A PhD examining forking
(Nyman, 2015)
"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" {{DEFAULTSORT:Fork (Software Development) Software project management