GPL linking exception - AbsoluteAstronomy.com

A GPL linking exception modifies the GNU General Public License

GNU General Public License

The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....

(GPL) to create a new, modified license. Such modified licenses enable software projects which provide library code, to be "linked to" the programs that use them, without applying the full terms of the GPL to the using program. Linking is the technical process of connecting code in a library to the using code, to produce a single executable file. It is performed either at compile time

Compile time

In computer science, compile time refers to either the operations performed by a compiler , programming language requirements that must be met by source code for it to be successfully compiled , or properties of the program that can be reasoned about at compile time.The operations performed at...

or run-time in order to produce functional machine-readable code. Without applying the linking exception, code linked with GPL code must be using a GPL-compatible license.
Many free software libraries which are distributed under the GPL use an equivalent exception, although the wording of the exception varies. Notable projects include GNU Guile

GNU Guile

GNU Guile is an interpreter/virtual machine for the Scheme programming language. It was first released in 1993. Guile includes modularized extensions for POSIX system calls, APL array functionality, and others packaged as an object library...

, the run-time libraries of GNAT

GNAT

GNAT is a free-software compiler for the Ada programming language which forms part of the GNU Compiler Collection. It supports all versions of the language, i.e. Ada 2005, Ada 95 and Ada 83; it allows already some constructs of Ada 2012...

, GNU Classpath

GNU Classpath

GNU Classpath is a project aiming to create a free software implementation of the standard class library for the Java programming language. Despite the massive size of the library to be created, the majority of the task is already done, including Swing, CORBA, and other major parts. The Classpath...

and the famous GCC Runtime Library Exception

Compiler runtime libraries also often use this license, e.g. the libgcc library in the GNU Compiler Collection

GNU Compiler Collection

The GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain...

uses a very similar linking exception, as well as all libraries of the Free Pascal

Free Pascal

Free Pascal Compiler is a free Pascal and Object Pascal compiler.In addition to its own Object Pascal dialect, Free Pascal supports, to varying degrees, the dialects of several other compilers, including those of Turbo Pascal, Delphi, and some historical Macintosh compilers...

project.

In 2007, Sun Microsystems released most of the source code

Source code

In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...

to the class libraries for the Java SE

Java Platform, Standard Edition

Java Platform, Standard Edition or Java SE is a widely used platform for programming in the Java language. It is the Java Platform used to deploy portable applications for general use...

and Java EE

Java Platform, Enterprise Edition

Java Platform, Enterprise Edition or Java EE is widely used platform for server programming in the Java programming language. The Java platform differs from the Java Standard Edition Platform in that it adds libraries which provide functionality to deploy fault-tolerant, distributed, multi-tier...

projects under version 2 of the GPL license plus the Classpath linking exception, and used the same license as one possible license for their enterprise server GlassFish

GlassFish

GlassFish is an open source application server project started by Sun Microsystems for the Java EE platform and now sponsored by Oracle Corporation. The supported version is called Oracle GlassFish Server...

. and for their NetBeans

NetBeans

NetBeans refers to both a platform framework for Java desktop applications, and an integrated development environment for developing with Java, JavaScript, PHP, Python, Groovy, C, C++, Scala, Clojure, and others...

Java IDE

Integrated development environment

An integrated development environment is a software application that provides comprehensive facilities to computer programmers for software development...

.

Version 3 of the GNU Lesser General Public License

GNU Lesser General Public License

The GNU Lesser General Public License or LGPL is a free software license published by the Free Software Foundation . It was designed as a compromise between the strong-copyleft GNU General Public License or GPL and permissive licenses such as the BSD licenses and the MIT License...

(LGPL) is likewise constructed as an exception to the GPL.

The classpath exception

The GNU Classpath

GNU Classpath

project provides an example of the use of such a GPL linking exception. The GNU Classpath library uses the following license:

Classpath is distributed under the terms of the GNU General Public License with the following clarification and special exception.

Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination.

As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obliged to do so. If you do not wish to do so, delete this exception statement from your version.

As such, it can be used to run, create and distribute a large class of applications and applets. When GNU Classpath is used unmodified as the core class library for a virtual machine, compiler for the Java language, or for a program written in the Java programming language it does not affect the licensing for distributing those programs directly.

The GNU Lesser General Public License

While version 2.1 of the LGPL was a standalone licence, the current LGPL version 3 is based on a reference to the GPL.

Compared to the GNU Classpath

GNU Classpath

license above, the LGPL formulates more requirements to the linking exception: you must allow modification of the portions of the Library you use and reverse engineering (of your program and the library) for debugging such modifications.

The classpath exception

The GNU Lesser General Public License

See also