The GNU General Public License (GPL) is one of the most widely used open source software licenses. It was created by the Free Software Foundation (FSF) to protect the GNU’s software from being made proprietary.
The GPL emphasizes the principles of software freedom and promotes the sharing of knowledge and collaboration. It is a copyleft license that requires any modified versions or derivative works to be licensed under the GPL.
Understanding the GPL is important to ensure that you’re using software in compliance with its license. To help you, here are some answers to the top 10 frequently asked questions about the GPL license.
Copyleft is a type of open-source software license that allows users to freely use, modify, and distribute software. The main purpose of a copyleft license is to ensure that the software remains free and open for subsequent users. Copyleft licenses typically require the source code to be made available to others, allowing them to modify and distribute it further, as long as any modifications or derivative works are also licensed under the same terms, thereby preventing the addition of further restrictions.
These licenses provide a legal framework that encourages developers to share their modifications, ensuring that the software remains accessible and modifiable by others.
Importantly, if you use a GPL component in your software, then your entire software is considered a ‘work based on a GPL’ and you must ensure that its use and distribution comply with the above conditions. Of course, this is a simple summary of the GPL terms and conditions. So, if you plan to use or distribute software under the GPL, you should consult the full legal text of the license to ensure compliance.
Yes. If someone violates the terms of the GPL by distributing software covered by the license without complying with its requirements, the copyright holder of the software can take legal action to enforce the license. This typically involves sending a cease and desist letter, requesting compliance with the terms, or seeking legal remedies through the court system.
Enforcement of the GPL has been successful, and violations have resulted in settlements, injunctions, and the like. Organizations such as the Free Software Foundation (FSF) defend the GPL and have taken legal action to protect software covered by the license.
The enforcement of the GPL may vary in different jurisdictions when copyright law differs. However, the GPL has been upheld in various legal systems around the world.
Yes. However, the GPL requires that the source code be made available to anyone who receives a copy of the software. Customers who purchase GPL-licensed software have the right to access and modify the underlying source code.
When you sell GPL-licensed software, you are essentially selling a copy of the software along with the rights and freedoms granted by the GPL. The GPL allows you to charge a fee for distributing the software, but you must also provide the recipients with the corresponding source code and grant them the same rights and freedoms that you received under the GPL.
Remember that the GPL is a copyleft license, which means that any modifications or derivative works based on the GPL-licensed software must also be distributed under the GPL.
The GPL is generally considered a strong copyleft license that’s safe to use. If you plan to combine GPL-licensed software with proprietary code, be aware that the entire project might need to be released under the GPL, which may not align with your business objectives. Always seek legal advice to ensure compliance with the license requirements.
There are currently two versions of the GPL license in operation: GPLv2 and GPLv3. The main differences between them are:
Importantly, although GPLv2 and GPLv3 differ in certain ways, they both share the core principles of free software and the four essential freedoms: the freedom to use, study, modify, and distribute software. So, the choice between GPLv2 and GPLv3 typically depends on the specific requirements and preferences of the project and its contributors.
Yes. If you use a GPL library in a project that’s released, the GPL requires that you release the source code of your entire project. This is because the GPL considers the combination of the library and your code as a derived work, subject to the copyleft requirements of the license. If you’ve modified a program’s source code for personal or internal use, there’s no need to release its source code. However, if you make the modified program available to the public, you must also make the code public.
It’s possible to do this with GPLv2 and GPLv3, although there are some restrictions. Nevertheless, the FSF has stated explicitly that GPLv3 is compatible with the Apache 2.0 license. However, there’s an issue with the original BSD license as it imposes a specific requirement that is not in the GPL (the requirement on advertisements of the program).
The GPL license states that any modifications or derivative works must be licensed. So, if you modify GPL-licensed software, you must distribute your modifications under the GPL as well.
Yes, if you make the source code of the GPL-licensed software available to your customers and you don’t restrict the distribution or modification rights of the GPL-licensed components. And you can link your proprietary software with a GPL library.
Remember that if you modify the GPL-licensed software or combine it with your code in a web application, you must also make the modified source code available to users of your web application upon request.
Make sure you either include a copy of the GPL license with any software you develop and distribute or make it available by providing instructions on how to obtain it. If you link your proprietary software with a GPL library and then distribute it, it’s vital that the entire application is licensed under the GPL, and you must provide the corresponding source code.
LGPL stands for the Lesser General Public License, and it’s more permissive than standard GPL. AGPL stands for the Affero General Public License, a variation of the GPL that caters to programs that run on a server. Their main differences lie in their scope and requirements.
The LGPL is compatible with the GPL. You can decide to “upgrade” to GPL and incorporate it in a wholly GPL-licensed project if you wish, but you can’t go the other way and re-license GPL-licensed code as LGPL.
AGPL extends the provisions of the GPL to cover software used over a network and programs running on a server. Under the AGPL, if a developer modifies a program, they must release the modified version of the program to everyone who uses the service.
AGPL has stronger copyleft requirements compared to LGPL. If you modify AGPL-licensed software, you must make the modified source code available to all users interacting with the software over a network, regardless of whether it is distributed or not.
If you use AGPL-licensed software over a network, even if you modify it, you must make the modified source code available to the users who interact with it, including the ability to download the source code from the networked application.
In summary, the LGPL is primarily used for software libraries and allows greater flexibility in combining the library with proprietary applications. The AGPL focuses on networked software and ensures that modifications made to the software are shared with users who interact with it over a network.
Understanding GPL licenses is crucial for developers and businesses working with open-source software. Nevertheless, always remember to consult legal professionals or experts for specific advice related to your situation.