When it comes to software development and licensing, the question of using GPL-licensed software in closed-source projects often arises. The GNU General Public License (GPL) is designed to promote the sharing of software source code and ensure that derivative works are also released under the same license. But is it possible to use GPL in a closed-source project? In this detailed answer, we’ll investigate 10 key aspects of this issue, each with added explanations.
I also made a quick video for those of you that don’t want to go into all the details of this which you can find here:
The Basics of GPL – What Does It Mean?
The GPL, created by the Free Software Foundation, is one of the most popular and widely used open-source licenses. It is intended to ensure that software remains free and open while giving credit to the original authors. There are different versions of GPL, with GPLv3 being the latest and most commonly adopted revision. The primary feature of any GPL version is a set of “four freedoms” that allow users to use, study, modify, and distribute the licensed software.
These freedoms are not without obligations, however. Key among these is the “copyleft” provision in GPL – this requires any modifications or derived work from the GPL licensed software to also be released under the same license. In other words, if you include GPL code in your project, you must release your entire software under the GPL as well.
For instance, let’s say you decide to use a library that is licensed under the GPL in your own application. If your application is distributed, either commercially or not, you must make your entire application’s source code available to others under the same GPL terms.
• Four Freedoms granted: use, study, modification, and distribution
• The “copyleft” provision ensures sharing of modifications
• The obligation to release the entire application under the GPL
Understanding the GPL License
The GPL is a widely-used and influential software license designed by the Free Software Foundation (FSF). It ensures that linked, derived, or modified versions of licensed software adhere to the same conditions as the original. The focus is on the users’ freedom to access, study, share, and modify software. When incorporating GPL-licensed elements into your project, you must comply with these requirements:
• You are bound to distribute the source code of your software.
• All derivations should be licensed under the GPL.
• Any changes made to the GPL-licensed software must be documented.
A classic scenario of GPL usage is an open-source project adopting a library or a module licensed under the GPL, which mandates making the entire project’s subsequent releases GPL-licensed.
The Closed-Source Challenge
Closed-source refers to proprietary software that restricts user access to the source code. The objective is to protect intellectual property, retain control over the software’s distribution, and profit from its commercial release. By keeping the source code secret, companies can maintain their competitive advantages and safeguard against unauthorized copying or modifications.
In practice, merging a GPL-covered component into a closed-source system contradicts licensing terms set by the GPL. For instance, if a company decides to include a GPL-licensed library within their closed-source software and later distributes the executable, the GPL would dictate that the entire source code be made accessible, contradicting the closed-source nature.
A Rare but Possible Coexistence
In some unique cases, utilizing GPL-licensed components in conjunction with closed-source software is allowed. This scenario emerges when the two entities are structurally separate and do not form a single work. To achieve this, they must communicate at arm’s length, primarily through pipes, sockets, or command-line arguments.
A long time ago I had used a GPL library in one of my systems and I ended up invoking it as a command line prompt and checking what it did and then using this. Is this a violation? Technically no since it’s not incorporated into my code in any shape or form however I still get to use and run it as part of my system. It would be the same as running any other system command from your operating system so it technically makes it perfectly legal.
I understand that in a lot of cases this may not be possible because you actually need to see result codes of your application or even have to use classes programmatically to do what you accomplish. However it does solve the case for most cases and it’s a good work-around that lets you stay legal and by the law of GPL.
Another example would be a multimedia player that supports various codecs is an example. The player’s core executable might be proprietary, while users can download and use codec plugins issued under the GPL license. These elements remain discrete and communicate via clearly defined interfaces.
• Identifying the line between derived and separate work is crucial.
• Communication between proprietary software and GPL-licensed components should be implemented carefully.
• Consulting legal professionals is essential to ensure compliance with GPL requirements.
Dynamic vs Static Linking
One of the most significant determining factors behind whether or not you can use GPL software as part of a closed-source project is the technique employed to link the components: dynamic or static linking. This aspect has legal implications and affects how the software operates as a whole.
Static linking requires copying portions of the GPL-licensed library into the resulting binary during compilation. Consequently, the output is considered a derivative work, subject to GPL conditions upon distribution. On the other hand, dynamic linking only includes references to the external library files, keeping their contents intact. Although legal debates exist surrounding this matter, many developers believe dynamic linking allows for separation between proprietary applications and GPL-covered components; however, caution is required.
• Adhering to dynamic linking lowers the risk of GPL violations.
• The FSF argues that both dynamic and static linking produce derivate works.
• Consult legal advice to determine if dynamic linking fits your specific case.
The Lesser GPL (LGPL)
While the GPL is restrictive concerning linking proprietary and open-source components, the Lesser GPL (LGPL) license was developed to address this concern. It enables developers to use LGPL-licensed libraries in closed-source projects without requiring them to release their source code.
The primary condition of using an LGPL-covered library involves dynamically linking to it and providing users with the ability to replace, modify, or upgrade the LGPL-licensed component without impacting your application’s functionality.
Here’s a company deciding to create a software that requires specific encryption algorithms available via an LGPL-compliant library. Including these algorithms won’t force the company to open-source its entire software: only the components linked to the LGPL-licensed library should be disclosed.
• LGPL permits combining open-source libraries with proprietary software.
• Companies must dynamically link to the LGPL library while allowing users to modify or update the LGPL portion.
• The LGPL fosters both open-source ideology and protection of intellectual property rights.
As you can understand from the above LGPL is a bit friendlier but you still need to take precautions to make sure you are a legally abiding by the licensing terms.
Several free and open-source licenses are considered compatible with the GPL requirements. They grant permission to mix the code under their particular license with GPL-covered components within a composite work, thereby generating a new work following the GPL terms. This approach can accommodate developers aiming for collaboration between open-source and proprietary software components.
For example, a team creates software utilizing an MIT-licensed library with no restrictions on distribution or modifications. Upon integrating a GPL-licensed component, they can legally distribute the resulting project under the GPL license.
• GPL-compatible licenses allow interaction with GPL-covered software.
• Examples include MIT, BSD 3-Clause, Apache License 2.0, among others.
• Note that GPL-compatibility doesn’t imply automatic conversion to the GPL license upon merging.
My personal favorite is the Apache and BSD licenses as they let you do a lot of things without taking away the original ownership of the person that implemented them. In fact if you see your Apple or Google phone you’d notice in the legal section a lot of licensing that was used and derived from open source projects while still maintaining a full closed source status in certain components.
Distribution and Copyleft Triggering
GPL’s copyleft becomes effective when a derivative work incorporating the GPL-licensed software gets distributed. In-house development and usage, for instance, does not require a GPL license agreement. Having said that, the GPL’s involvement should be dealt with cautiously.
Imagine an organization using a GPL-covered library for internal use without releasing their software publicly. They are permitted to maintain source code confidentiality; nevertheless, once they decide to distribute it, GPL requirements must be acknowledged, and the source code disclosed accordingly.
• The copyleft is triggered when distributing the derivative work.
• Internal usage of GPL-covered components can keep the source code private.
• When planning distribution, considering alternative licenses, or seeking legal advice is critical.
This one is very important to keep at bay to avoid getting in trouble and triggering a legal clause for GPL and closed source applications.
Contributing to the GPL Ecosystem
Many developers opt for contributing to open-source projects under the GPL or other free licenses, thus promoting innovation and community involvement in software development. In situations where proprietary and GPL-licensed elements need to interact, convertible licenses like the LGPL can offer viable alternatives.
By releasing newly developed libraries, tools, or modules under GPL-related licenses, developers promote knowledge sharing and collaborations amongst industry professionals.
• Open-source development supports mutual learning and advancement.
• Adapting your own component releases with GPL-compatible licenses allows collaboration.
• Alternative licenses such as LGPL provide flexibility while maintaining freedom-access principles.
While it’s nice to be a contributor as a closed source maintainer to an open source GPL library it’s not mandatory it just shows you can play nice and give back to the community.
Importance of Documentation and Licensing Attribution
For any project involving open-source components, thoroughly documenting all incorporated components and their respective licenses helps avoid legal disputes or intellectual property conflicts. GPL/Linux-using developers should offer a comprehensive documentation listing:
• The included open-source components
• Component origin and authors
• Related license terms
With explicitly documented components, users and contributors receive accurate information necessary to follow licensing requirements. This practice fosters transparency and protection against potential legal issues.
• Always document the used GPL-covered elements within your software.
• Proper attribution includes providing details on origins, authors, and the exact license terms.
• Conforming to these standards minimizes legal risks and strengthens trust with users.
Believe it or not sometimes just referencing for the original is nice but also can keep you out from a lot of trouble so make sure you attribute anything you use.
While the combination of GPL software and closed-source projects is challenging to achieve, there are cases where it is possible through a distinct separation. Employing techniques such as dynamic linking or opting for LGPL components can offer viable solutions. Always consult legal professionals to ensure compliance with GPL requirements and minimize potential risks. Ultimately, understanding and acknowledging licensing agreements promotes collaboration, innovation, and successfully sharing knowledge in the software development community.
My experience is entirely with US legal entities and regulations. I think a lot of it applies internationally too but I do not have a lot of expertise on information on anything besides US law when it comes to closed source GPL. Hope you enjoyed this and was able to give some insights for your use on GPL. If you think you need to know more please reach out to an IP lawyer as they are the ones that have the most information on the topic.