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The GNU General Public License (GNU GPL or simply GPL) is a series of widely used
free software license A free-software license is a notice that grants the recipient of a piece of software extensive rights to modify and redistribute that software. These actions are usually prohibited by copyright law, but the rights-holder (usually the author) ...
s that guarantee end users the
four freedoms The Four Freedoms were goals articulated by U.S. President Franklin D. Roosevelt on Monday, January 6, 1941. In an address known as the Four Freedoms speech (technically the 1941 State of the Union address), he proposed four fundamental freed ...
to run, study, share, and modify the software. The license was the first
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 ...
for general use and was originally written by the founder of the
Free Software Foundation The Free Software Foundation (FSF) is a 501(c)(3) non-profit organization founded by Richard Stallman on October 4, 1985, to support the free software movement, with the organization's preference for software being distributed under copyleft (" ...
(FSF),
Richard Stallman Richard Matthew Stallman (; born March 16, 1953), also known by his initials, rms, is an American free software movement activist and programmer. He campaigns for software to be distributed in such a manner that its users have the freedom to ...
, for the
GNU Project The GNU Project () is a free software, mass collaboration project announced by Richard Stallman on September 27, 1983. Its goal is to give computer users freedom and control in their use of their computers and computing devices by collaborat ...
. The license grants the recipients of a
computer program A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components. A computer program ...
the rights of
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 ...
. These GPL series are all copyleft licenses, which means that any derivative work must be distributed under the same or equivalent license terms. It is more restrictive than the Lesser General Public License and even further distinct from the more widely used permissive software licenses
BSD The Berkeley Software Distribution or Berkeley Standard Distribution (BSD) is a discontinued operating system based on Research Unix, developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berk ...
,
MIT The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...
, and Apache. Historically, the GPL license family has been one of the most popular software licenses in the free and open-source software domain. Prominent free software programs licensed under the GPL include the Linux kernel and the
GNU Compiler Collection The GNU Compiler Collection (GCC) is an optimizing compiler produced by the GNU Project supporting various programming languages, hardware architectures and operating systems. The Free Software Foundation (FSF) distributes GCC as free softwar ...
(GCC). David A. Wheeler argues that the copyleft provided by the GPL was crucial to the success of
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, w ...
-based systems, giving the programmers who contributed to the kernel the assurance that their work would benefit the whole world and remain free, rather than being exploited by software companies that would not have to give anything back to the community. In 2007, the third version of the license (GPLv3) was released to address some perceived problems with the second version (GPLv2) which were discovered during the latter's long-time usage. To keep the license up to date, the GPL license includes an optional "any later version" clause, allowing users to choose between the original terms or the terms in new versions as updated by the FSF. Developers can omit it when licensing their software; the Linux kernel, for instance, is licensed under GPLv2 without the "any later version" clause. The "or any later version" clause also known as a lifeboat clause allows combinations between different versions of GPL licensed software to maintain compatibility. For example
Inkscape Inkscape is a free and open-source vector graphics editor used to create vector images, primarily in Scalable Vector Graphics (SVG) format. Other formats can be imported and exported. Inkscape can render primitive vector shapes (e.g. rec ...
is under the GPLv2 or any later version, but includes code under LGPLv3 or any later version, so effectively the binary as a whole is under the GPLv3 or any later version.


History

The GPL was written by
Richard Stallman Richard Matthew Stallman (; born March 16, 1953), also known by his initials, rms, is an American free software movement activist and programmer. He campaigns for software to be distributed in such a manner that its users have the freedom to ...
in 1989, for use with programs released as part of the GNU project. The original GPL was based on a unification of similar licenses used for early versions of
GNU Emacs GNU Emacs is a free software text editor. It was created by GNU Project founder Richard Stallman, based on the Emacs editor developed for Unix operating systems. GNU Emacs has been a central component of the GNU project and a flagship project of ...
(1985), the
GNU Debugger The GNU Debugger (GDB) is a portable debugger that runs on many Unix-like systems and works for many programming languages, including Ada, C, C++, Objective-C, Free Pascal, Fortran, Go, and partially others. History GDB was first written ...
, and the
GNU C Compiler The GNU Compiler Collection (GCC) is an optimizing compiler produced by the GNU Project supporting various programming languages, hardware architectures and operating systems. The Free Software Foundation (FSF) distributes GCC as free software ...
. These licenses contained similar provisions to the modern GPL, but were specific to each program, rendering them incompatible, despite being the same license. Stallman's goal was to produce one license that could be used for any project, thus making it possible for many projects to share code. The second version of the license, version 2, was released in 1991. Over the following 15 years, members of the
free software community The free software movement is a social movement with the goal of obtaining and guaranteeing certain freedoms for software users, namely the freedoms to run the software, to study the software, to modify the software, and to share copies of the s ...
became concerned over problems in the GPLv2 license that could let someone exploit GPL-licensed software in ways contrary to the license's intent. These problems included
tivoization Tivoization is the practice of designing hardware that incorporates software under the terms of a copyleft software license like the GNU General Public License (GNU GPL), but uses hardware restrictions or digital rights management (DRM) to preve ...
(the inclusion of GPL-licensed software in hardware that refuses to run modified versions of its software), compatibility issues similar to those of the
Affero General Public License The Affero General Public License (Affero GPL and informally Affero License) is a free software license. The first version of the Affero General Public License (AGPLv1), was published by Affero, Inc. in March 2002, and based on the GNU General P ...
, and patent deals between
Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washin ...
and distributors of free and open-source software, which some viewed as an attempt to use patents as a weapon against the free software community. Version 3 was developed to attempt to address these concerns and was officially released on 29 June 2007.


Version 1

Version 1 of the GNU GPL, released on 25 February 1989, prevented what were then the two main ways that software distributors restricted the freedoms that define free software. The first problem was that distributors may publish
binary file A binary file is a computer file that is not a text file. The term "binary file" is often used as a term meaning "non-text file". Many binary file formats contain parts that can be interpreted as text; for example, some computer document fil ...
s only—executable, but not readable or modifiable by humans. To prevent this, GPLv1 stated that copying and distributing copies or any portion of the program must also make the human-readable source code available under the same licensing terms. The second problem was that distributors might add restrictions, either to the license or by combining the software with other software that had other restrictions on distribution. The union of two sets of restrictions would apply to the combined work, thus adding unacceptable restrictions. To prevent this, GPLv1 stated that modified versions, as a whole, had to be distributed under the terms in GPLv1. Therefore, software distributed under the terms of GPLv1 could be combined with software under more permissive terms, as this would not change the terms under which the whole could be distributed. However, software distributed under GPLv1 could not be combined with software distributed under a more restrictive license, as this would conflict with the requirement that the whole be distributable under the terms of GPLv1.


Version 2

According to Richard Stallman, the major change in GPLv2 was the "Liberty or Death" clause, as he calls it – Section 7. The section says that licensees may distribute a GPL-covered work ''only'' if they can satisfy all of the license's obligations, despite any other legal obligations they might have. In other words, the obligations of the license may not be severed due to conflicting obligations. This provision is intended to discourage any party from using a patent infringement claim or other litigation to impair users' freedom under the license. By 1990, it was becoming apparent that a less restrictive license would be strategically useful for the
C library The C standard library or libc is the standard library for the C programming language, as specified in the ISO C standard. ISO/IEC (2018). '' ISO/IEC 9899:2018(E): Programming Languages - C §7'' Starting from the original ANSI C standard, it was ...
and for software libraries that essentially did the job of existing proprietary ones; when version 2 of the GPL (GPLv2) was released in June 1991, therefore, a second license – the GNU Library General Public License – was introduced at the same time and numbered with version 2 to show that both were complementary. The version numbers diverged in 1999 when version 2.1 of the LGPL was released, which renamed it the
GNU Lesser General Public License The GNU Lesser General Public License (LGPL) is a free-software license published by the Free Software Foundation (FSF). The license allows developers and companies to use and integrate a software component released under the LGPL into their own ...
to reflect its place in the philosophy. The GPLv2 was also modified to refer to the new name of the LGPL, but its version number remained the same, resulting in the original GPLv2 not being recognised by the Software Package Data Exchange (SPDX). The license includes instructions to specify "version 2 of the License, or (at your option) any later version" to allow the flexible optional use of either version 2 or 3, but some developers change this to specify "version 2" only.


Version 3

In late 2005, the
Free Software Foundation The Free Software Foundation (FSF) is a 501(c)(3) non-profit organization founded by Richard Stallman on October 4, 1985, to support the free software movement, with the organization's preference for software being distributed under copyleft (" ...
(FSF) announced work on version 3 of the GPL (GPLv3). On 16 January 2006, the first "discussion draft" of GPLv3 was published, and the public consultation began. The public consultation was originally planned for nine to fifteen months, but finally stretched to eighteen months with four drafts being published. The official GPLv3 was released by the FSF on 29 June 2007. GPLv3 was written by Richard Stallman, with legal counsel from
Eben Moglen Eben Moglen (born 1959) is an American legal scholar who is professor of law and legal history at Columbia University, and is the founder, Director-Counsel and Chairman of Software Freedom Law Center. Professional biography Moglen started out as ...
and
Richard Fontana Richard Fontana is a lawyer in the United States who is particularly known for his work in the area of open source and free software. Fontana works at Red Hat. Before Red Hat he was counsel at the Software Freedom Law Center (SFLC). In 2012 Fontana ...
from the
Software Freedom Law Center The Software Freedom Law Center (SFLC) is an organization that provides '' pro bono'' legal representation and related services to not-for-profit developers of free software/open source software. It was launched in February 2005 with Eben Moglen ...
. According to Stallman, the most important changes were in relation to
software patents A software patent is a patent on a piece of software, such as a computer program, libraries, user interface, or algorithm. Background A patent is a set of exclusionary rights granted by a state to a patent holder for a limited period of time, u ...
,
free software license A free-software license is a notice that grants the recipient of a piece of software extensive rights to modify and redistribute that software. These actions are usually prohibited by copyright law, but the rights-holder (usually the author) ...
compatibility, the definition of "source code", and
hardware restrictions A hardware restriction (sometimes called hardware DRM) is low-level protection enforced by electronic components. The hardware restriction scheme may protect against physical or malware attacks or complement a digital rights management system imp ...
on software modifications, such as
tivoization Tivoization is the practice of designing hardware that incorporates software under the terms of a copyleft software license like the GNU General Public License (GNU GPL), but uses hardware restrictions or digital rights management (DRM) to preve ...
.Interview with Richard Stallman
, Free Software Magazine, 23 January 2008.
Other changes related to internationalization, how license violations are handled, and how additional permissions could be granted by the copyright holder. The concept of "software propagation", as a term for the copying and duplication of software, was explicitly defined. The public consultation process was coordinated by the Free Software Foundation with assistance from Software Freedom Law Center,
Free Software Foundation Europe The Free Software Foundation Europe (FSFE) is an ''eingetragener Verein'' (registered voluntary association) under German law. It was founded in 2001 to support all aspects of the free software movement in Europe, with registered chapters in seve ...
, and other free software groups. Comments were collected from the public via the gplv3.fsf.org web portal, using purpose-written software called stet. During the public consultation process, 962 comments were submitted for the first draft. By the end of the comment period, a total of 2,636 comments had been submitted. The third draft was released on 28 March 2007. This draft included language intended to prevent patent-related agreements such as the controversial Microsoft-Novell patent agreement, and restricted the anti-tivoization clauses to a legal definition of a "user" and a "consumer product". It also explicitly removed the section on "Geographical Limitations", whose probable removal had been announced at the launch of the public consultation. The fourth discussion draft, which was the last, was released on 31 May 2007. It introduced Apache License version 2.0 compatibility (prior versions are incompatible), clarified the role of outside contractors and made an exception to avoid the perceived problems of a Microsoft–Novell style agreement, saying in Section 11 paragraph 6 that: This aimed to make future such deals ineffective. The license was also meant to cause Microsoft to extend the patent licenses it granted to Novell customers for the use of GPLv3 software to ''all'' users of that GPLv3 software; this was possible only if Microsoft was legally a "conveyor" of the GPLv3 software. Early drafts of GPLv3 also let licensors add an Affero-like requirement that would have plugged the '' ASP loophole in the GPL''.List of free-software licences on the FSF website
"We recommend that developers consider using the GNU AGPL for any software which will commonly be run over a network."
As there were concerns expressed about the administrative costs of checking code for this additional requirement, it was decided to keep the GPL and the Affero license separated. Others, notably some high-profile Linux kernel developers such as
Linus Torvalds Linus Benedict Torvalds ( , ; born 28 December 1969) is a Finnish software engineer who is the creator and, historically, the lead developer of the Linux kernel, used by Linux distributions and other operating systems such as Android. He also ...
,
Greg Kroah-Hartman Greg Kroah-Hartman (GKH) is a major Linux kernel developer. he is the Linux kernel maintainer for the branch, the staging subsystem, USB, driver core, debugfs, kref, kobject, and the sysfs kernel subsystems, Userspace I/O (with Hans J. Koc ...
, and Andrew Morton, commented to the mass media and made public statements about their objections to parts of discussion drafts 1 and 2. The kernel developers referred to GPLv3 draft clauses regarding
DRM DRM may refer to: Government, military and politics * Defense reform movement, U.S. campaign inspired by Col. John Boyd * Democratic Republic of Madagascar, a former socialist state (1975–1992) on Madagascar * Direction du renseignement milita ...
/
Tivoization Tivoization is the practice of designing hardware that incorporates software under the terms of a copyleft software license like the GNU General Public License (GNU GPL), but uses hardware restrictions or digital rights management (DRM) to preve ...
, patents, and "additional restrictions", and warned of a
Balkanisation Balkanization is the fragmentation of a larger region or state into smaller regions or states, which may be hostile or uncooperative with one another. It is usually caused by differences of ethnicity, culture, and religion and some other factor ...
of the "Open Source Universe". Linus Torvalds, who decided not to adopt the GPLv3 for the Linux kernel, reiterated his criticism several years later. GPLv3 improved compatibility with several free software licenses such as the Apache License, version 2.0, and the GNU Affero General Public License, which GPLv2 could not be combined with. However, GPLv3 software could only be combined and share code with GPLv2 software if the GPLv2 license used had the optional "or later" clause and the software was upgraded to GPLv3. While the "GPLv2 or any later version" clause is considered by FSF as the most common form of licensing GPLv2 software,
Toybox Toybox is a free and open-source software implementation of over 200 Unix command line utilities such as '' ls'', '' cp'', and '' mv''. The Toybox project was started in 2006, and became a 0BSD licensed BusyBox alternative. Toybox is used for mo ...
developer Rob Landley described it as a ''lifeboat clause''. Software projects licensed with the optional "or later" clause include the
GNU Project The GNU Project () is a free software, mass collaboration project announced by Richard Stallman on September 27, 1983. Its goal is to give computer users freedom and control in their use of their computers and computing devices by collaborat ...
, while a prominent example without the clause is the Linux kernel. The final version of the license text was published on 29 June 2007.


Terms and conditions

The terms and conditions of the GPL must be made available to anybody receiving a copy of the work that has a GPL applied to it ("the licensee"). Any licensee who adheres to the terms and conditions is given permission to modify the work, as well as to copy and redistribute the work or any derivative version. The licensee is allowed to charge a fee for this service or do this free of charge. This latter point distinguishes the GPL from software licenses that prohibit commercial redistribution. The FSF argues that free software should not place restrictions on commercial use, and the GPL explicitly states that GPL works may be sold at any price. The GPL additionally states that a distributor may not impose "further restrictions on the rights granted by the GPL". This forbids activities such as distributing the software under a non-disclosure agreement or contract. The fourth section for version 2 of the license and the seventh section of version 3 require that programs distributed as pre-compiled binaries be accompanied by a copy of the source code, a written offer to distribute the source code via the same mechanism as the pre-compiled binary, or the written offer to obtain the source code that the user got when they received the pre-compiled binary under the GPL. The second section of version 2 and the fifth section of version 3 also require giving "all recipients a copy of this License along with the Program". Version 3 of the license allows making the source code available in additional ways in fulfillment of the seventh section. These include downloading source code from an adjacent network server or by peer-to-peer transmission, provided that is how the compiled code was available and there are "clear directions" on where to find the source code. The FSF does not hold the copyright for a work released under the GPL unless an author explicitly assigns copyrights to the FSF (which seldom happens except for programs that are part of the GNU project). Only the individual copyright holders have the authority to sue when a license violation is suspected.


Use of licensed software

Software under the GPL may be run for all purposes, including commercial purposes and even as a tool for creating
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 ...
, such as when using GPL-licensed
compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...
s. Users or companies who distribute GPL-licensed works (e.g. software), may charge a fee for copies or give them free of charge. This distinguishes the GPL from shareware software licenses that allow copying for personal use but prohibit the commercial distribution or proprietary licenses where copying is prohibited by
copyright law 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 ...
. The FSF argues that freedom-respecting free software should also not restrict commercial use and distribution (including redistribution): In purely private (or internal) use—with no sales and no distribution—the software code may be modified and parts reused without requiring the source code to be released. For sales or distribution, the entire source code needs to be made available to end users, including any code changes and additions—in that case, copyleft is applied to ensure that end users retain the freedoms defined above. However, software running as an application program under a GPL-licensed operating system such as Linux is not required to be licensed under GPL or to be distributed with source-code availability—the licensing depends only on the used libraries and software components and not on the underlying platform. For example, if a program consists only of original
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 ...
, or is combined with source code from other
software component Component-based software engineering (CBSE), also called component-based development (CBD), is a branch of software engineering that emphasizes the separation of concerns with respect to the wide-ranging functionality available throughout a give ...
s, then the custom software components need not be licensed under GPL and need not make their source code available; even if the underlying operating system used is licensed under the GPL, applications running on it are not considered derivative works. Only if GPLed parts are used in a program (and the program is distributed), then all other source code of the program needs to be made available under the same license terms. The GNU ''Lesser'' General Public License (LGPL) was created to have a weaker copyleft than the GPL, in that it does not require custom-developed source code (distinct from the LGPL'ed parts) to be made available under the same license terms. The fifth section of version 3 states that no GPL-licensed code shall be considered an effective "technical protection measure" as defined by Article 11 of the
WIPO Copyright Treaty The World Intellectual Property Organization Copyright Treaty (WIPO Copyright Treaty or WCT) is an international treaty on copyright law adopted by the member states of the World Intellectual Property Organization (WIPO) in 1996. It provides addi ...
, and that those who convey the work waive all legal power to prohibit circumvention of the technical protection measure "to the extent such circumvention is effected by exercising rights under this License with respect to the covered work". This means that users cannot be held liable for circumventing DRM implemented using GPLv3-licensed code under laws such as the U.S.
Digital Millennium Copyright Act The Digital Millennium Copyright Act (DMCA) is a 1998 United States copyright law that implements two 1996 treaties of the World Intellectual Property Organization (WIPO). It criminalizes production and dissemination of technology, devices, or ...
(DMCA).


Copyleft

The distribution rights granted by the GPL for modified versions of the work are not unconditional. When someone distributes a GPL'ed work plus their own modifications, the requirements for distributing the whole work cannot be any greater than the requirements that are in the GPL. This requirement is known as copyleft. It earns its legal power from the use of
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 ...
on software programs. Because a GPL work is copyrighted, a licensee has no right to redistribute it, not even in modified form (barring
fair use Fair use is a doctrine in United States law that permits limited use of copyrighted material without having to first acquire permission from the copyright holder. Fair use is one of the limitations to copyright intended to balance the interests ...
), except under the terms of the license. One is only required to adhere to the terms of the GPL if one wishes to exercise rights normally restricted by copyright law, such as redistribution. Conversely, if one distributes copies of the work without abiding by the terms of the GPL (for instance, by keeping the source code secret), they can be
sued - A lawsuit is a proceeding by a party or parties against another in the civil court of law. The archaic term "suit in law" is found in only a small number of laws still in effect today. The term "lawsuit" is used in reference to a civil acti ...
by the original author under copyright law. Copyright law has historically been used to prevent distribution of work by parties not authorized by the creator. Copyleft uses the same copyright laws to accomplish a very different goal. It grants rights to distribution to all parties insofar as they provide the same rights to subsequent ones, and they to the next, etc. In this way the GPL and other copyleft licenses attempt to enforce
libre Libre may refer to: Computing * Libre software, free software * Libre Computer Project, developer of open-hardware single-board computers Medicine * FreeStyle Libre, a glucose monitoring device Media * Libre Times, news site which people can fr ...
access to the work and all derivatives. Many distributors of GPL'ed programs bundle the source code with the executables. An alternative method of satisfying the copyleft is to provide a written offer to provide the source code on a physical medium (such as a CD) upon request. In practice, many GPL'ed programs are distributed over the Internet, and the source code is made available over
FTP The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. FTP is built on a client–server model architecture using separate control and data ...
or
HTTP The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide We ...
. For Internet distribution, this complies with the license. Copyleft applies only when a person seeks to redistribute the program. Developers may make private modified versions with no obligation to divulge the modifications, as long as they do not distribute the modified software to anyone else. Copyleft applies only to the software, and not to its output (unless that output is itself a derivative work of the program). For example, a public web portal running a modified derivative of a GPL'ed content management system is not required to distribute its changes to the underlying software, because the modified web portal is not being redistributed but rather hosted, and also because the web portal output is also not a derivative work of the GPL'ed content management system. There has been debate on whether it is a violation of the GPL to release the source code in
obfuscated Obfuscation is the obscuring of the intended meaning of communication by making the message difficult to understand, usually with confusing and ambiguous language. The obfuscation might be either unintentional or intentional (although intent u ...
form, such as in cases in which the author is less willing to make the source code available. The consensus was that while unethical, it was not considered a violation. The issue was clarified when the license was altered with v2 to require that the "preferred" version of the source code be made available.


License versus contract

The GPL was designed as a license, rather than a contract. In some
Common Law In law, common law (also known as judicial precedent, judge-made law, or case law) is the body of law created by judges and similar quasi-judicial tribunals by virtue of being stated in written opinions."The common law is not a brooding omnipres ...
jurisdictions, the legal distinction between a license and a contract is an important one: contracts are enforceable by
contract law A contract is a legally enforceable agreement between two or more parties that creates, defines, and governs mutual rights and obligations between them. A contract typically involves the transfer of goods, services, money, or a promise to tran ...
, whereas licenses are enforced under
copyright law 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 ...
. However, this distinction is not useful in the many jurisdictions where there are no differences between contracts and licenses, such as Civil Law systems. Those who do not accept the GPL's terms and conditions do not have permission, under copyright law, to copy or distribute GPL-licensed software or derivative works. However, if they do not redistribute the GPL'ed program, they may still use the software within their organization however they like, and works (including programs) constructed by the use of the program are not required to be covered by this license. Software developer
Allison Randal Allison Randal is a software developer and author. She was the chief architect of the Parrot virtual machine, a member of the board of directors for The Perl Foundation, a director of the Python Software Foundation from 2010 to 2012, and th ...
argued that the GPLv3 as a license is unnecessarily confusing for lay readers, and could be simplified while retaining the same conditions and legal force. In April 2017, a US federal court ruled that an open-source license is an enforceable contract. In October 2021 SFC sued Vizio over breach of contract as an end user to request source code to Vizio's TVs, a federal judge has ruled in the interim that the GPL is an enforceable contract by end users as well as a license for copyright holders.


Derivations

The text of the GPL is itself
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 ...
ed, and the copyright is held by the Free Software Foundation. The FSF permits people to create new licenses based on the GPL, as long as the derived licenses do not use the GPL preamble without permission. This is discouraged, however, since such a license might be incompatible with the GPL and causes a perceived
license proliferation License proliferation is the phenomenon of an abundance of already existing and the continued creation of new software licenses for software and software packages in the FOSS ecosystem. License proliferation affects the whole FOSS ecosystem neg ...
. Other licenses created by the GNU project include the
GNU Lesser General Public License The GNU Lesser General Public License (LGPL) is a free-software license published by the Free Software Foundation (FSF). The license allows developers and companies to use and integrate a software component released under the LGPL into their own ...
, GNU Free Documentation License, and
Affero General Public License The Affero General Public License (Affero GPL and informally Affero License) is a free software license. The first version of the Affero General Public License (AGPLv1), was published by Affero, Inc. in March 2002, and based on the GNU General P ...
. The text of the GPL is not itself under the GPL. The license's copyright disallows modification of the license. Copying and distributing the license is allowed since the GPL requires recipients to get "a copy of this License along with the Program". According to the GPL FAQ, anyone can make a new license using a modified version of the GPL as long as they use a different name for the license, do not mention "GNU", and remove the preamble, though the preamble can be used in a modified license if permission to use it is obtained from the Free Software Foundation (FSF).


Linking and derived works


Libraries

According to the FSF, "The GPL does not require you to release your modified version or any part of it. You are free to make modifications and use them privately, without ever releasing them." However, if one releases a GPL-licensed entity to the public, there is an issue regarding linking: namely, whether a proprietary program that uses a GPL library is in violation of the GPL. This key dispute is whether non-GPL software can legally statically link or dynamically link to GPL libraries. Different opinions exist on this issue. The GPL is clear in requiring that all derivative works of code under the GPL must themselves be under the GPL. Ambiguity arises with regards to using GPL libraries, and bundling GPL software into a larger package (perhaps mixed into a binary via static linking). This is ultimately a question not of the GPL ''per se'', but of how copyright law defines derivative works. The following points of view exist:


Point of view: dynamic and static linking violate GPL

The Free Software Foundation (which holds the copyright of several notable GPL-licensed software products and of the license text itself) asserts that an executable that uses a dynamically linked library is indeed a derivative work. This does not, however, apply to separate programs communicating with one another. The Free Software Foundation also created the LGPL, which is nearly identical to the GPL, but with additional permissions to allow linking for the purposes of "using the library". Richard Stallman and the FSF specifically encourage library writers to license under the GPL so that proprietary programs cannot use the libraries, in an effort to protect the free-software world by giving it more tools than the proprietary world.


Point of view: static linking violates GPL but unclear as of dynamic linking

Some people believe that while
static linking In computer science, a static library or statically-linked library is a set of routines, external functions and variables which are resolved in a caller at compile-time and copied into a target application by a compiler, linker, or binder, produ ...
produces derivative works, it is not clear whether an executable that dynamically links to a GPL code should be considered a derivative work (see weak copyleft). Linux author Linus Torvalds agrees that dynamic linking can create derived works but disagrees over the circumstances. A Novell lawyer has written that dynamic linking not being derivative "makes sense" but is not "clear-cut", and that evidence for good-intentioned dynamic linking can be seen by the existence of proprietary Linux kernel drivers. In ''
Galoob v. Nintendo ''Lewis Galoob Toys, Inc. v. Nintendo of America, Inc.'' is a 1992 legal case where the United States Court of Appeals for the Ninth Circuit concluded that there was no copyright infringement made by the Game Genie, a video game accessory that ...
'', the United States
Ninth Circuit Court of Appeals The United States Court of Appeals for the Ninth Circuit (in case citations, 9th Cir.) is the U.S. federal court of appeals that has appellate jurisdiction over the U.S. district courts in the following federal judicial districts: * District ...
defined a derivative work as having form' or permanence" and noted that "the infringing work must incorporate a portion of the copyrighted work in some form", but there have been no clear court decisions to resolve this particular conflict.


Point of view: linking is irrelevant

According to an article in the '' Linux Journal'', Lawrence Rosen (a one-time
Open Source Initiative The Open Source Initiative (OSI) is the steward of the Open Source Definition, the set of rules that define open source software. It is a California public-benefit nonprofit corporation,_with_501(c)(3).html" ;"title="110. - 6910./ref> is a type o ...
general counsel) argues that the method of linking is mostly irrelevant to the question about whether a piece of software is a derivative work; more important is the question about whether the software was intended to interface with client software and/or libraries.Lawrence Rosen
Derivative Works
''Linux Journal'' (1 January 2003).
He states, "The primary indication of whether a new program is a derivative work is whether the source code of the original program was used n a copy-paste sense modified, translated or otherwise changed in any way to create the new program. If not, then I would argue that it is not a derivative work," and lists numerous other points regarding intent, bundling, and linkage mechanism. He further argues on his firm's website that such "market-based" factors are more important than the linking technique. There is also the specific issue of whether a plugin or
module Module, modular and modularity may refer to the concept of modularity. They may also refer to: Computing and engineering * Modular design, the engineering discipline of designing complex devices using separately designed sub-components * Mo ...
(such as the
NVidia Nvidia CorporationOfficially written as NVIDIA and stylized in its logo as VIDIA with the lowercase "n" the same height as the uppercase "VIDIA"; formerly stylized as VIDIA with a large italicized lowercase "n" on products from the mid 1990s to ...
or
ATI Ati or ATI may refer to: * Ati people, a Negrito ethnic group in the Philippines **Ati language (Philippines), the language spoken by this people group ** Ati-Atihan festival, an annual celebration held in the Philippines *Ati language (China), a ...
graphics card
kernel module In computing, a loadable kernel module (LKM) is an object file that contains code to extend the running kernel, or so-called ''base kernel'', of an operating system. LKMs are typically used to add support for new hardware (as device drivers) and/o ...
s) must also be GPL, if it could reasonably be considered its own work. This point of view suggests that reasonably separate plugins, or plugins for software designed to use plugins, could be licensed under an arbitrary license if the work is GPLv2. Of particular interest is the GPLv2 paragraph: The GPLv3 has a different clause: As a case study, some supposedly proprietary plugins and
theme Theme or themes may refer to: * Theme (arts), the unifying subject or idea of the type of visual work * Theme (Byzantine district), an administrative district in the Byzantine Empire governed by a Strategos * Theme (computing), a custom graphical ...
s/
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different de ...
s for GPLv2
CMS CMS may refer to: Computing * Call management system * CMS-2 (programming language), used by the United States Navy * Code Morphing Software, a technology used by Transmeta * Collection management system for a museum collection * Color manag ...
software such as Drupal and
WordPress WordPress (WP or WordPress.org) is a free and open-source content management system (CMS) written in hypertext preprocessor language and paired with a MySQL or MariaDB database with supported HTTPS. Features include a plugin architecture ...
have come under fire, with both sides of the argument taken. The FSF differentiates on how the plugin is being invoked. If the plugin is invoked through dynamic linkage and it performs function calls to the GPL program then it is most likely a derivative work.


Communicating and bundling with non-GPL programs

The mere act of communicating with other programs does not, by itself, require all software to be GPL; nor does distributing GPL software with non-GPL software. However, minor conditions must be followed that ensures the rights of GPL software are not restricted. The following is a quote from the gnu.org GPL FAQ, which describes to what extent software is allowed to communicate with and be bundled with GPL programs: The FSF thus draws the line between "library" and "other program" via 1) "complexity" and "intimacy" of information exchange and 2) mechanism (rather than semantics), but resigns that the question is not clear-cut and that in complex situations, case law will decide.


Legal status

The first known violation of the GPL was in 1989, when
NeXT Next may refer to: Arts and entertainment Film * ''Next'' (1990 film), an animated short about William Shakespeare * ''Next'' (2007 film), a sci-fi film starring Nicolas Cage * '' Next: A Primer on Urban Painting'', a 2005 documentary film Lit ...
extended the GCC compiler to support
Objective-C Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. Originally developed by Brad Cox and Tom Love in the early 1980s, it was selected by NeXT for its NeXT ...
, but did not publicly release the changes. After an inquiry they created a public
patch Patch or Patches may refer to: Arts, entertainment and media * Patch Johnson, a fictional character from ''Days of Our Lives'' * Patch (''My Little Pony''), a toy * "Patches" (Dickey Lee song), 1962 * "Patches" (Chairmen of the Board song) ...
. There was no lawsuit filed for this violation. In 2002,
MySQL AB MySQL AB was a Swedish software company founded in 1995. It was acquired by Sun Microsystems in 2008, Sun was in turn acquired by Oracle Corporation in 2010. MySQL AB is the creator of MySQL, a relational database management system, as well as ...
sued Progress NuSphere for copyright and trademark infringement in
United States district court The United States district courts are the trial courts of the U.S. federal judiciary. There is one district court for each federal judicial district, which each cover one U.S. state or, in some cases, a portion of a state. Each district co ...
. NuSphere had allegedly violated MySQL's copyright by linking MySQL's GPL'ed code with NuSphere Gemini table without complying with the license. After a preliminary hearing before Judge Patti Saris on 27 February 2002, the parties entered settlement talks and eventually settled. After the hearing, FSF commented that "Judge Saris made clear that she sees the GNU GPL to be an enforceable and binding license." In August 2003, the
SCO Group The SCO Group (often referred to SCO and later called The TSG Group) was an American software company in existence from 2002 to 2012 that became known for owning Unix operating system assets that had belonged to the Santa Cruz Operation (the ...
stated that they believed the GPL to have no legal validity and that they intended to pursue lawsuits over sections of code supposedly copied from SCO Unix into the Linux kernel. This was a problematic stand for them, as they had distributed Linux and other GPL'ed code in their
Caldera OpenLinux Caldera OpenLinux (COL) is a defunct Linux distribution. Caldera originally introduced it in 1997 based on the German LST Power Linux distribution, and then taken over and further developed by Caldera Systems (now SCO Group) since 1998. A suc ...
distribution, and there is little evidence that they had any legal right to do so except under the terms of the GPL. In February 2018, after federal circuit court judgement, appeal, and the case being (partially) remanded to the circuit court, the parties restated their remaining claims and provided a plan to move toward final judgement. The remaining claims revolved around
Project Monterey Project Monterey was an attempt to build a single Unix operating system that ran across a variety of 32-bit and 64-bit platforms, as well as supporting multi-processing. Announced in October 1998, several Unix vendors were involved; IBM provide ...
, and were finally settled in November 2021 by IBM paying $14.25 million to the TSG (previously SCO) bankruptcy trustee. In April 2004, the
netfilter Netfilter is a framework provided by the Linux kernel that allows various networking-related operations to be implemented in the form of customized handlers. Netfilter offers various functions and operations for packet filtering, network add ...
/
iptables iptables is a user-space utility program that allows a system administrator to configure the IP packet filter rules of the Linux kernel firewall, implemented as different Netfilter modules. The filters are organized in different tables, which ...
project was granted a preliminary injunction against Sitecom Germany by
Munich Munich ( ; german: München ; bar, Minga ) is the capital and most populous city of the German state of Bavaria. With a population of 1,558,395 inhabitants as of 31 July 2020, it is the third-largest city in Germany, after Berlin and Ha ...
District Court after Sitecom refused to desist from distributing Netfilter's GPL'ed software in violation of the terms of the GPL.
Harald Welte Harald Welte, also known as LaForge, is a German programmer. Welte is the founder of the free software project Osmocom and was formerly involved in the netfilter/iptables and Openmoko projects. He is a member of the Chaos Computer Club. Bi ...
, of Netfilter, was represented by
ifrOSS Institut für Rechtsfragen der Freien und Open Source Software, abbreviated to ifrOSS, (English: ''Institute for legal issues regarding free and open source software'') is a German organisation that provides legal services for free software. ifrOS ...
co-founder Till Jaeger. In July 2004, the German court confirmed this injunction as a final ruling against Sitecom. The court's justification was that: :Defendant has infringed on the copyright of plaintiff by offering the software 'netfilter/iptables' for download and by advertising its distribution, without adhering to the license conditions of the GPL. Said actions would only be permissible if the defendant had a license grant.... This is independent of the questions whether the licensing conditions of the GPL have been effectively agreed upon between plaintiff and defendant or not. If the GPL were not agreed upon by the parties, defendant would notwithstanding lack the necessary rights to copy, distribute, and make the software 'netfilter/iptables' publicly available. This exactly mirrored the predictions given previously by the FSF's Eben Moglen. This ruling was important because it was the first time that a court had confirmed that violating terms of the GPL could be a copyright violation and established jurisprudence as to the enforceability of the GPLv2 under German law. In May 2005, Daniel Wallace filed suit against the Free Software Foundation in the
Southern District of Indiana The United States District Court for the Southern District of Indiana (in case citations, S.D. Ind.) is a United States district court, federal district court in Indiana. It was created in 1928 by an act of Congress of the United States, Congress ...
, contending that the GPL is an illegal attempt to fix prices (at zero). The suit was dismissed in March 2006, on the grounds that Wallace had failed to state a valid antitrust claim; the court noted that "the GPL encourages, rather than discourages, free competition and the distribution of computer operating systems, the benefits of which directly pass to consumers".Dismissal
of Wallace v. FSF. Fro
this article
on Groklaw.
Wallace was denied the possibility of further amending his complaint, and was ordered to pay the FSF's legal expenses. On 8 September 2005, the Seoul Central District Court ruled that the GPL was not material to a case dealing with
trade secret Trade secrets are a type of intellectual property that includes formulas, practices, processes, designs, instruments, patterns, or compilations of information that have inherent economic value because they are not generally known or readily ...
s derived from GPL-licensed work. Defendants argued that since it is impossible to maintain trade secrets while being compliant with GPL and distributing the work, they are not in breach of trade secrets. This argument was considered without ground. On 6 September 2006, the
gpl-violations.org gpl-violations.org is a not-for-profit project founded and led by Harald Welte in 2004. It works to make sure software licensed under the GNU General Public License is not used in ways prohibited by the license. Goals The goals of the project are ...
project prevailed in court litigation against
D-Link D-Link Corporation is a Taiwanese multinational networking equipment manufacturing corporation headquartered in Taipei, Taiwan. It was founded in March 1986 in Taipei as ''Datex Systems Inc.'' History D-Link Corporation changed its name fr ...
Germany GmbH regarding D-Link's copyright-infringing use of parts of the Linux kernel in storage devices they distributed. The judgment stated that the GPL is valid, legally binding, and stands in German court. In late 2007, the
BusyBox BusyBox is a software suite that provides several Unix utilities in a single executable file. It runs in a variety of POSIX environments such as Linux, Android, and FreeBSD, although many of the tools it provides are designed to work with in ...
developers and the
Software Freedom Law Center The Software Freedom Law Center (SFLC) is an organization that provides '' pro bono'' legal representation and related services to not-for-profit developers of free software/open source software. It was launched in February 2005 with Eben Moglen ...
embarked upon a program to gain GPL compliance from distributors of BusyBox in
embedded system An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' ...
s, suing those who would not comply. These were claimed to be the first US uses of courts for enforcement of GPL obligations. (See BusyBox GPL lawsuits.) On 11 December 2008, the Free Software Foundation sued Cisco Systems, Inc. for copyright violations by its Linksys division, of the FSF's GPL-licensed
coreutils The GNU Core Utilities or coreutils is a package of GNU software containing implementations for many of the basic tools, such as cat, ls, and rm, which are used on Unix-like operating systems. In September 2002, the ''GNU coreutils'' were cr ...
, readline,
Parted GNU Parted (the name being the conjunction of the two words PARTition and EDitor) is a free partition editor, used for creating and deleting partitions. This is useful for creating space for new operating systems, reorganising hard disk usage, ...
,
Wget GNU Wget (or just Wget, formerly Geturl, also written as its package name, wget) is a computer program that retrieves content from web servers. It is part of the GNU Project. Its name derives from "World Wide Web" and " ''get''." It supports do ...
,
GNU Compiler Collection The GNU Compiler Collection (GCC) is an optimizing compiler produced by the GNU Project supporting various programming languages, hardware architectures and operating systems. The Free Software Foundation (FSF) distributes GCC as free softwar ...
,
binutils The GNU Binary Utilities, or , are a set of programming tools for creating and managing binary programs, object files, libraries, profile data, and assembly source code. Tools They were originally written by programmers at Cygnus Solutions. ...
, and
GNU Debugger The GNU Debugger (GDB) is a portable debugger that runs on many Unix-like systems and works for many programming languages, including Ada, C, C++, Objective-C, Free Pascal, Fortran, Go, and partially others. History GDB was first written ...
software packages, which Linksys distributes in the Linux firmware of its
WRT54G The Linksys WRT54G Wi-Fi series is a series of Wi-Fi–capable residential gateways marketed by Linksys, a subsidiary of Cisco from 2003 until acquired by Belkin in 2013. A ''residential gateway'' connects a local area network (such as a home netw ...
wireless router A wireless router is a device that performs the functions of a router and also includes the functions of a wireless access point. It is used to provide access to the Internet or a private computer network. Depending on the manufacturer and mode ...
s, as well as numerous other devices including DSL and Cable modems, Network Attached Storage devices, Voice-Over-IP gateways, virtual private network devices, and a home theater/media player device. After six years of repeated complaints to
Cisco Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, ...
by the FSF, claims by Cisco that they would correct, or were correcting, their compliance problems (not providing complete copies of all source code and their modifications), of repeated new violations being discovered and reported with more products, and lack of action by Linksys (a process described on the FSF blog as a "five-years-running game of Whack-a-Mole") the FSF took them to court. Cisco settled the case six months later by agreeing "to appoint a Free Software Director for Linksys" to ensure compliance, "to notify previous recipients of Linksys products containing FSF programs of their rights under the GPL," to make source code of FSF programs freely available on its website, and to make a monetary contribution to the FSF. In 2011, it was noticed that GNU Emacs had been accidentally releasing some binaries without corresponding source code for two years, in opposition to the intended spirit of the
GPL The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general u ...
, resulting in a
copyright violation Copyright infringement (at times referred to as piracy) is the use of works protected by copyright without permission for a usage where such permission is required, thereby infringing certain exclusive rights granted to the copyright holder, s ...
. Richard Stallman described this incident as a "very bad mistake", which was promptly fixed. The FSF did not sue any downstream redistributors who also unknowingly violated the GPL by distributing these binaries. In 2017 Artifex, the maker of
Ghostscript Ghostscript is a suite of software based on an interpreter for Adobe Systems' PostScript and Portable Document Format (PDF) page description languages. Its main purposes are the rasterization or rendering of such page description language file ...
, sued
Hancom Hancom (KOSDAQ: HAANSOFT) is an office suite software developer in South Korea. Established in 1990, the company created Hangul, a native word processing program for the Korean language. In May 2017 Hancom lost a lawsuit in US Federal Court for v ...
, the maker of an office suite which included Ghostscript. Artifex offers two licenses for Ghostscript; one is the Affero GPL License and the other is a commercial license. Hancom did not acquire a commercial license from Artifex nor did it release its office suite as free software. Artifex sued Hancom in US District Court and made two claims. First, Hancom's use of Ghostscript was a violation of copyright; and second, Hancom's use of Ghostscript was a license violation. Judge
Jacqueline Scott Corley Jacqueline Scott Corley (née Jacqueline Marie Scott, born 1966) is a United States district judge of the United States District Court for the Northern District of California. She served as a United States magistrate judge of the same court from ...
found the GPL license was an enforceable contract and Hancom was in breach of contract. On 20 July 2021, the developers of the open-source Stockfish chess engine sued ChessBase, the creator of chess software, for violating the GPLv3 license. It was claimed that Chessbase had made only slight modifications to the Stockfish code and sold the new engines (Fat Fritz 2 and Houdini 6) to their customers. Additionally, Fat Fritz 2 was marketed as if it was an innovative engine. ChessBase had infringed on the license by not distributing these products as Free Software in accordance with the GPL. A year later on 7 November 2022, both parties reached an agreement and ended the dispute. In the near future ChessBase will no longer sell products containing Stockfish code, while informing their customers of this fact with an appropriate notice on their web pages. However, one year later, Chessbase's license would be reinstated. Stockfish did not seek damages or financial compensation.


Compatibility and multi-licensing

Code licensed under several other licenses can be combined with a program under the GPL without conflict, as long as the combination of restrictions on the work as a whole does not put any additional restrictions beyond what GPL allows. In addition to the regular terms of the GPL, there are additional restrictions and permissions one can apply: # If a user wants to combine code licensed under different versions of GPL, then this is only allowed if the code with the earlier GPL version includes an "or any later version" statement. For instance, the GPLv3-licensed GNU LibreDWG library cannot be used anymore by
LibreCAD LibreCAD is a computer-aided design (CAD) application for 2D design. It is free and open-source, and available for Linux, macOS, and Windows operating systems. Most of the interface and handle concepts are analogous to AutoCAD, making it easier ...
and
FreeCAD FreeCAD is a general-purpose parametric 3D computer-aided design (CAD) modeler and a building information modeling (BIM) software application with finite element method (FEM) support. It is intended for mechanical engineering product design bu ...
who have GPLv2-only dependencies. # Code licensed under LGPL is permitted to be linked with any other code no matter what license that code has, though the LGPL does add additional requirements for the combined work. LGPLv3 and GPLv2-only can thus commonly not be linked, as the combined Code work would add additional LGPLv3 requirements on top of the GPLv2-only licensed software. Code licensed under LGPLv2.x without the "any later version" statement can be relicensed if the whole combined work is licensed to GPLv2 or GPLv3. FSF maintains a list of GPL-
compatible Compatibility may refer to: Computing * Backward compatibility, in which newer devices can understand data generated by older devices * Compatibility card, an expansion card for hardware emulation of another device * Compatibility layer, compo ...
free software licenses containing many of the most common free software licenses, such as the original MIT/X license, the
BSD license BSD licenses are a family of permissive free software licenses, imposing minimal restrictions on the use and distribution of covered software. This is in contrast to copyleft licenses, which have share-alike requirements. The original BSD lice ...
(in its current 3-clause form), and the
Artistic License Artistic license (alongside more contextually-specific derivative terms such as poetic license, historical license, dramatic license, and narrative license) refers to deviation from fact or form for artistic purposes. It can include the alterat ...
2.0. Starting from GPLv3, it is unilaterally compatible for materials (like text and other media) under
Creative Commons Attribution-ShareAlike 4.0 International License A Creative Commons (CC) license is one of several public copyright licenses that enable the free distribution of an otherwise copyrighted "work".A "work" is any creative material made by a person. A painting, a graphic, a book, a song/lyrics ...
to be remixed into the GPL-licensed materials (prominently software), not vice versa, for niche use cases like game engine (GPL) with game scripts (CC BY-SA). David A. Wheeler has advocated that free/open source software developers use only GPL-compatible licenses, because doing otherwise makes it difficult for others to participate and contribute code. As a specific example of license incompatibility, Sun Microsystems'
ZFS ZFS (previously: Zettabyte File System) is a file system with volume management capabilities. It began as part of the Sun Microsystems Solaris operating system in 2001. Large parts of Solaris – including ZFS – were published under an ope ...
cannot be included in the GPL-licensed Linux kernel, because it is licensed under the GPL-incompatible Common Development and Distribution License. Furthermore, ZFS is protected by patents, so distributing an independently developed GPL-ed implementation would still require Oracle's permission. A number of businesses use
multi-licensing Multi-licensing is the practice of distributing software under two or more different sets of terms and conditions. This may mean multiple different software licenses or sets of licenses. Prefixes may be used to indicate the number of license ...
to distribute a GPL version and sell a
proprietary {{Short pages monitor