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 (even proprietary) software without being required by the terms of a strong

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, ...

license to release the source code of their own components. However, any developer who modifies an LGPL-covered component is required to make their modified version available under the same LGPL license. For proprietary software, code under the LGPL is usually used in the form of a shared library, so that there is a clear separation between the proprietary and LGPL components. The LGPL is primarily used for

software libraries In computer science, a library is a collection of non-volatile resources used by computer programs, often for software development. These may include configuration data, documentation, help data, message templates, pre-written code and subro ...

, although it is also used by some stand-alone applications. The LGPL was developed as a compromise between the strong

of the

GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end user In product development, an end user (sometimes end-user) is a person who ultimately uses or is intended to ulti ...

(GPL) and more permissive licenses such as the BSD licenses and the MIT License. The word "Lesser" in the title shows that the LGPL does not guarantee the end user's complete freedom in the use of software; it only guarantees the freedom of modification for components licensed under the LGPL, but not for any proprietary components.

History

The license was originally called the GNU Library General Public License and was first published in 1991, and adopted the version number 2 for parity with GPL version 2. The LGPL was revised in minor ways in the 2.1 point release, published in 1999, when it was renamed the GNU Lesser General Public License to reflect the FSF's position that not all libraries should use it. Version 3 of the LGPL was published in 2007 as a list of additional permissions applied to GPL version 3. In addition to the term "work based on the Program" of GPL, LGPL version 2 introduced two additional clarification terms "work based on the library" and a "work that uses the library". LGPL version 3 partially dropped these terms.

Differences from the GPL

The main difference between the GPL and the LGPL is that the latter allows the work to be linked with (in the case of a library, "used by") a non-(L)GPLed program, regardless of whether it is licensed under a license of GPL family or other licenses.Stallman, Richard
Why you shouldn't use the Lesser GPL for your next library
Free Software Foundation official website. In LGPL 2.1, the non-(L)GPLed program can then be distributed under any terms if it is not a

derivative work In copyright law, a derivative work is an expressive creation that includes major copyrightable elements of an original, previously created first work (the underlying work). The derivative work becomes a second, separate work independent in fo ...

. If it is a derivative work, then the program's terms must allow for "modification of the work for the customer's own use and

reverse engineering Reverse engineering (also known as backwards engineering or back engineering) is a process or method through which one attempts to understand through deductive reasoning how a previously made device, process, system, or piece of software accompli ...

for debugging such modifications." Whether a work that uses an LGPL program is a derivative work or not is a legal issue. A standalone executable that dynamically links to a library through a

.so .so is the internet country code top-level domain (ccTLD) for Somalia. After a long absence, the .so domain was officially relaunched on November 1, 2010, by .SO Registry, which is regulated by the nation's Ministry of Posts and Telecommunicatio ...

, .dll, or similar medium is generally accepted as not being a derivative work as defined by the LGPL. It would fall under the definition of a "work that uses the Library". Paragraph 5 of the LGPL version 2.1 states: :A program that contains no derivative of any portion of the Library, but is designed to work with the Library by being compiled or linked with it, is called a "work that uses the Library". Such a work, in isolation, is not a derivative work of the Library, and therefore falls outside the scope of this License. Essentially, if it is a "work that uses the library", then it must be possible for the software to be linked with a newer version of the LGPL-covered program. The most commonly used method for doing so is to use "a suitable shared library mechanism for linking". Alternatively, a statically linked library is allowed if either source code or linkable object files are provided.Gnu Lesser General Public License, Section 4
pt. d) 0)

Compatibility

One feature of the LGPL is the permission to sublicense under the GPL any piece of software which is received under the LGPL (see section 3 of the LGPL version 2.1, and section 2 option b of the LGPL version 3). This feature allows for direct reuse of LGPLed code in GPLed libraries and applications. Version 3 of the LGPL is not inherently compatible with version 2 of the GPL. However, works using the latter that have given permission to use a later version of the GPL are compatible:
Free Software Foundation official website. a work released under the GPLv2 "or any later version" may be combined with code from a LGPL version 3 library, with the combined work as a whole falling under the terms of the GPLv3.Frequently Asked Questions about the GNU Licenses - GNU Project - Free Software Foundation
Free Software Foundation official website.

FSF recommendations on library licensing

The former name ''GNU Library General Public License'' gave some the impression that the FSF recommended that all software libraries should use the LGPL and programs should use the GPL. In 1999 essay ''Why you shouldn't use the Lesser GPL for your next library'' Richard Stallman explained that while the LGPL had not been deprecated, one should not necessarily use the LGPL for all libraries, as using GPL can give advantage to free-software developers. On the other hand, the FSF sometimes advocate for even less restrictive licenses. For example, Stallman endorsed the use of BSD-style license by the Vorbis project in its libraries in 2001.Stallman, Richard
Re: [open-source
[Fwd: [icecast-dev">pen-source">Re: [open-source
[Fwd: [icecast-devXiph.org announces Vorbis Beta 4 and the Xiph.org]

Programming language specifications

The license uses terminology which is mainly intended for applications written in the C (programming language), C programming language or its family. Franz Inc., the developers of Allegro Common Lisp, published their own preamble to the license to clarify terminology in the

Lisp A lisp is a speech impairment in which a person misarticulates sibilants (, , , , , , , ). These misarticulations often result in unclear speech. Types * A frontal lisp occurs when the tongue is placed anterior to the target. Interdental lisping ...

context. The LGPL with this preamble is sometimes referred to as the LLGPL.Preamble to the Gnu Lesser General Public License
/ref> In addition, Ada has a special feature,

generics Generic or generics may refer to: In business * Generic term, a common name used for a range or class of similar things not protected by trademark * Generic brand, a brand for a product that does not have an associated brand or trademark, other ...

, which may prompt the use of the GNAT Modified General Public License (GMGPL): it allows code to link against or instantiate GMGPL-covered units without the code itself becoming covered by the GPL. C++ templates and header-only libraries have the same problem as Ada generics. Version 3 of the LGPL addresses such cases in section 3.

Class inheritance

Some concern has risen about the suitability of object-oriented classes in LGPL-licensed code being inherited by non-(L)GPL code. Clarification is given on the official GNU website: :The LGPL does not contain special provisions for inheritance, because none are needed. Inheritance creates derivative works in the same way as traditional linking, and the LGPL permits this type of derivative work in the same way as it permits ordinary function calls.Turner, David
The LGPL and Java
GNU official website.

References

External links

LGPL Official PageDerivative WorksLisping Copyleft: A Close Reading of the Lisp LGPL, 5 International Free and Open Source Software Law Review 15 (2013)
{{DEFAULTSORT:Gnu Lesser General Public License Computer law Copyleft Free and open-source software licenses Copyleft software licenses GNU Project