Managing copyright ownership
The nature of copyright ownership in free software bears clarifying. In the absence of a Contributor License Agreement or similar document (a practice we strongly recommend against), how do free software developers and publishers manage the legal rights associated with the software’s copyright?
Who owns a free software project?
When you contribute to a free software project, if you do not assign your copyright to someone else, you retain ownership over the intellectual property rights associated with your contribution. Your changes are then licensed to everyone else, including the other copyright holders, under the same terms as the license the project was distributed under in the first place.
As such, in most cases, the copyright for any free software project is held in aggregate by all of the people who have contributed intellectual property to it, who license it to users, and each other, with a free software license.
It may be desirable for some projects, particularly commercial projects, to formally establish the following for each contribution:
- The contributor owns the copyright for their contribution, or is authorized by the copyright holder to use it
- The contributor agrees to license their copyright under the terms of the project license
If it is desirable for your project to formally establish provenance in this manner, we recommend the use of the Developer Certificate of Origin. Most projects facilitate this by asking authors to “sign-off” on their contributions. The Git version control system provides a means of indicating that a given contribution has been signed-off on with the “git commit -s” flag.
Changing a project’s license
You may at some point wish to change your project’s license.
If the project is licensed with a permissive license, generally speaking it is possible to sublicense the original project with a new license, and apply the new license to future changes. You will still have to comply with the original license terms, such as attribution, but future changes may be licensed under different terms. In this sense, changing the license is similar to starting a new project and incorporating the original codebase into it.
However, if the project is licensed with a copyleft license, this is more difficult – often impossible. This is an intended trait of copyleft licenses: it is necessary in order to prevent the project from being incorporated into non-free software. You cannot generally sublicense a copyleft project in the same way you can license a permissive project.
It is possible to change the license of a copyleft project, but you must either
It is for this reason that holding the copyright in aggregate among the contributors, rather than assigning copyright to a single entity, is recommended for copyleft projects: it strengthens the long-term security of the project’s free software status by making it more difficult to change it to a non-free license.