GPL vs. LGPL

Attribute	GPL	LGPL
License Type	Strong Copyleft	Weak Copyleft
Derivative Works	Must be licensed under GPL	Can be licensed under any license
Linking with Non-Free Software	Not allowed	Allowed
Compatibility with Proprietary Software	Not compatible	Compatible
Library Usage	Can be used as a library	Can be used as a library
License Notice	Must retain GPL license notice	Must retain LGPL license notice
Dynamic Linking	Requires GPL for dynamically linked code	Allows dynamic linking with proprietary code
Static Linking	Requires GPL for statically linked code	Allows static linking with proprietary code

Introduction

When it comes to open-source software licenses, the GNU General Public License (GPL) and the GNU Lesser General Public License (LGPL) are two of the most widely used and influential licenses. Both licenses are developed and maintained by the Free Software Foundation (FSF) and share a common goal of promoting software freedom. However, there are distinct differences between GPL and LGPL that make them suitable for different types of projects and use cases. In this article, we will explore the attributes of GPL and LGPL, highlighting their similarities and differences, and discussing the scenarios in which each license is most appropriate.

GPL: The Copyleft License

The GNU General Public License (GPL) is a copyleft license, which means that any derivative work or modifications made to the original software must also be licensed under the GPL. This ensures that the software and its derivatives remain free and open-source. One of the key attributes of GPL is its strong copyleft nature, which guarantees that the source code of the software is always available to users and developers. This encourages collaboration, transparency, and the sharing of improvements within the community.

Another important aspect of GPL is its viral nature. When a software project is licensed under GPL, any software that links or combines with it must also be licensed under GPL. This requirement ensures that the entire software ecosystem surrounding a GPL-licensed project remains open-source. This attribute has been instrumental in fostering the growth of the open-source community and preventing proprietary software from taking advantage of open-source projects without contributing back.

Additionally, GPL provides strong protections for users' freedom. It includes provisions that prevent the software from being restricted or locked down by proprietary means. This ensures that users have the freedom to study, modify, and distribute the software as they see fit. By enforcing these freedoms, GPL empowers users to take control of their software and encourages a culture of collaboration and innovation.

LGPL: The Lesser Copyleft License

The GNU Lesser General Public License (LGPL) is a variant of the GPL that offers more flexibility in certain scenarios. While LGPL also promotes software freedom, it has a less restrictive copyleft nature compared to GPL. One of the key attributes of LGPL is its ability to allow proprietary software to dynamically link with libraries licensed under LGPL without requiring the proprietary software to be licensed under LGPL as well.

This attribute makes LGPL particularly suitable for libraries and frameworks that are intended to be used by both open-source and proprietary software. By allowing proprietary software to link with LGPL-licensed libraries, LGPL encourages wider adoption and usage of the library, even in commercial applications. This flexibility has made LGPL a popular choice for many widely-used libraries, such as the GNU C Library (glibc) and the Qt framework.

However, it is important to note that if modifications are made to the LGPL-licensed library itself, those modifications must be released under LGPL. This ensures that any improvements or changes to the library are contributed back to the open-source community. This requirement helps maintain the collaborative nature of open-source development and ensures that the library continues to evolve and improve over time.

Choosing Between GPL and LGPL

When deciding between GPL and LGPL for a software project, several factors need to be considered. The primary factor is the level of copyleft desired for the project. If strong copyleft is desired, ensuring that all derivative works are also open-source, then GPL is the appropriate choice. This is particularly relevant for projects that aim to create a comprehensive ecosystem of open-source software or those that want to prevent proprietary software from taking advantage of their work without contributing back.

On the other hand, if the project is a library or framework that is intended to be widely adopted and used by both open-source and proprietary software, LGPL provides a more permissive option. LGPL allows proprietary software to dynamically link with the library without requiring the proprietary software to be licensed under LGPL. This flexibility can be advantageous for libraries that want to maximize their adoption and usage, even in commercial applications.

Another consideration is the potential impact on the community and ecosystem surrounding the project. GPL's strong copyleft nature ensures that the entire software ecosystem remains open-source, fostering collaboration and preventing proprietary software from exploiting open-source projects. However, this can also deter some commercial entities from using or contributing to the project. LGPL, with its more permissive copyleft, may attract a wider range of contributors and users, including those from the proprietary software world.

It is also worth noting that the choice of license is not set in stone and can be changed in the future. However, changing the license of a project can be a complex process, especially if there are multiple contributors involved. Therefore, it is important to carefully consider the license choice at the outset of the project to avoid potential complications down the line.

Conclusion

In summary, both GPL and LGPL are powerful open-source licenses that promote software freedom and collaboration. GPL's strong copyleft nature ensures that derivative works and the entire software ecosystem remain open-source, while LGPL offers more flexibility, particularly for libraries and frameworks that want to be widely adopted by both open-source and proprietary software. The choice between GPL and LGPL depends on the desired level of copyleft, the project's goals, and the impact on the community and ecosystem. By understanding the attributes of GPL and LGPL, developers can make informed decisions when selecting the appropriate license for their projects, ultimately contributing to the growth and success of the open-source community.