GNU Lesser General Public License
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The GNU Lesser General Public License (formerly the GNU Library General Public License) is an FSF approved Free Software license designed as a compromise between the GNU General Public License and simple permissive licenses such as the BSD license and the MIT License. It was written in 1991 (and updated in 1999) by Richard Stallman and Eben Moglen.
The main difference between the GPL and the LGPL is that the latter can be linked to a non-(L)GPLed program, which may be free software or proprietary.
The LGPL places copyleft restrictions on the program itself but does not apply these restrictions to other software that merely links with the program. There are, however, certain other restrictions on this software. Essentially, it must be possible for the software to be linked with a newer version of the LGPL-covered program.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, static linking is allowed if either source code or linkable object files are provided.
The LGPL is primarily intended for software libraries, although it is also used by applications such as OpenOffice.org and Mozilla.
One feature of the LGPL is that one can convert any LGPLed piece of software into a GPLed piece of software (section 3 of the license). This feature is useful if one wants to create a version of the code that software companies cannot use in proprietary software products. It is also necessary to ensure that the LGPL is "GPL-compatible", so that GPL-covered programs can use LGPL-covered libraries.
The former name of "GNU Library General Public License" gave some people the impression that the FSF wanted all libraries to use the LGPL and all programs to use the GPL. In 1999, Richard Stallman wrote an essay explaining why this was not the case, and that one shouldn't necessarily use the LGPL for libraries.
- Which license is best for a given library is a matter of strategy, and it depends on the details of the situation. At present, most GNU libraries are covered by the Library GPL, and that means we are using only one of these two strategies [allowing/disallowing proprietary programs to use a library] , neglecting the other. So we are now seeking more libraries to release under the ordinary GPL.
Contrary to popular impression, however, this does not mean that the FSF deprecates the LGPL, but merely says that it shouldn't be used for all libraries — the same essay goes on to say:
- Using the ordinary GPL is not advantageous for every library. There are reasons that can make it better to use the Library GPL in certain cases.
Indeed, the Stallman and the FSF sometimes advocate licenses even less restrictive than the LGPL as a matter of strategy (to maximize the freedom of users). A prominent example was Stallman's endorsement of the use of a BSD-style license by the Vorbis project for its libraries [1] (http://lwn.net/2001/0301/a/rms-ov-license.php3).
See also
- List of programs released under the GPL
- BSD and GPL licensing
- GNU Free Documentation License
- GNU General Public License
- GNAT Modified General Public License
External links
- Text of the new "Lesser" GPL (http://www.gnu.org/copyleft/lesser.html)
- Text of the old "Library" GPL (http://www.gnu.org/copyleft/lgpl.html)
- Richard Stallman, "Why you shouldn't use the Library GPL for your next library (http://www.gnu.org/licenses/why-not-lgpl.html)" (February 1999).de:GNU Lesser General Public License
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