GPL vs. LGPL-2.1

Attribute	GPL	LGPL-2.1
License Type	Strong copyleft	Weak copyleft
Derivative Works	Must be licensed under GPL	Can be linked with proprietary software
Compatibility	Not compatible with proprietary software	Compatible with proprietary software
Dynamic Linking	Requires GPL for dynamic linking	Allows dynamic linking with proprietary software
Usage	Primarily for free and open-source software	Allows for wider usage in proprietary software

Introduction

When it comes to open-source licenses, two of the most popular choices are the GNU General Public License (GPL) and the GNU Lesser General Public License (LGPL) version 2.1. Both licenses are created by the Free Software Foundation (FSF) and are designed to protect the rights of users and developers of open-source software. While they share some similarities, there are also key differences between the two licenses that developers should be aware of when choosing which license to use for their projects.

Scope of Application

One of the main differences between GPL and LGPL-2.1 is the scope of application. The GPL is a copyleft license, which means that any derivative works of a GPL-licensed software must also be licensed under the GPL. This ensures that the source code of the software remains open and freely available to users. On the other hand, the LGPL-2.1 is a more permissive license that allows developers to link their proprietary software with LGPL-licensed libraries without having to release the source code of their own software.

Compatibility

Another important factor to consider when choosing between GPL and LGPL-2.1 is compatibility with other licenses. The GPL is known for its strong copyleft provisions, which can make it incompatible with some other open-source licenses. This can be a concern for developers who want to combine GPL-licensed code with code under a different license. On the other hand, the LGPL-2.1 is designed to be more compatible with other licenses, making it a better choice for projects that require the use of multiple libraries with different licensing terms.

Dynamic Linking

One of the key features of the LGPL-2.1 is its provision for dynamic linking. This allows developers to link their software with LGPL-licensed libraries at runtime without having to release the source code of their own software. This can be particularly useful for developers who want to create proprietary software that relies on open-source libraries for certain functionalities. The GPL, on the other hand, requires that any software that is linked with GPL-licensed code must also be licensed under the GPL, which can be a limitation for developers of proprietary software.

Modification of Code

Both GPL and LGPL-2.1 require that any modifications made to the licensed code must be released under the same license. However, the LGPL-2.1 provides an exception for static linking, allowing developers to link their software with LGPL-licensed libraries without having to release the source code of their own software. This can be a significant advantage for developers who want to create proprietary software that uses open-source libraries for certain functionalities. The GPL, on the other hand, does not provide this exception, making it more restrictive in terms of code modification.

Conclusion

In conclusion, both GPL and LGPL-2.1 are popular choices for open-source licenses, each with its own set of advantages and limitations. The GPL is a strong copyleft license that ensures the source code of the software remains open and freely available to users, while the LGPL-2.1 is a more permissive license that allows for dynamic linking and is more compatible with other licenses. Developers should carefully consider the scope of application, compatibility, dynamic linking, and code modification requirements of each license before choosing which one to use for their projects.