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Can a copyright holder of a GPL licensed project grant permission to allow another project to use it under the terms of a different license?

The GNU/GPL is a copyleft license, which means that derivative work can only be distributed under the same license terms [https://en.wikipedia.org/wiki/GNU_General_Public_License].

For example, the copyright owner of a project under a GPL license could grant permission to a project that uses a license such as MIT or BSD to distribute their work (in whole or in part) under that more permissive license. If this is allowed, are there any caveats to doing this?

  • Do you know of multi-licensing? – unor Aug 31 '17 at 10:52
  • I'm aware that a project can have multiple licences. My question focuses on the specific case of one project allowing an exception specifically for another project to include its source code. – Gunther Aug 31 '17 at 11:59
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    Not well versed in this, but afaik the answer is yes, but it requires the express permission of all copyright holders - which means everyone and anyone who has ever contributed something to the project, no matter how small. So for example if you have accepted pull requests to "your" GPL project then you need express written permission from that author too. (Mozilla did this when they changed license and it took many many years.) – AnorZaken Aug 31 '17 at 13:15
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You can release your intellectual property to different people under different license conditions. This is not just permissible, it is a common business model commonly known as multi-licensing. It is not uncommon to release a GPL-licensed version of a software gratis, but also offer a paid version under a license which allows to distribute derivative works under proprietary licenses.

This business model works well for frameworks, middleware, libraries and other software which is usually used as a base to develop other applications. With the GPL-version, those other applications must also be GPL-licensed, which limits the monetization options. But when you buy the proprietary license, you have far more options, including pay-by-install.

The MIT and BSD are rarely a good choice for this business model, though, because they allow redistribution under the same terms. So anyone you sell a BSD or MIT license to would then be able to underbid you. A paid license for an open source project usually does not allow to relicense the sourcecode of the derivatives to other parties.

Still, you see software multi-licensed under GPL, MIT and/or BSD. So if you don't feel like taking sides in the endless discussion about which open source license is the most free one, you can simply let people choose under which software license they prefer to use your software.

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    That is why selling support is the root of profit. Others can underbid, but large corporations doesn't like taking chances when it comes to professional support - and presumably the original authors can provide the best support and an entity that is merely underbidding / reselling is less trustworthy. So I think that's why we see GPL + MIT in some cases - others can copy the product but they can not copy trust. – AnorZaken Aug 31 '17 at 13:24
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    @Philipp your answer is fine, but the question has no mention of commercial licensing options. I am upvoting nonetheless! – Philippe Ombredanne Sep 1 '17 at 9:35
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    @DavidSchwartz That's a common misconception. OS software is often licensed to the whole world by putting it on a public webserver. But you can also license it to only one specific person. That other person then holds a license but can give other people a license if they want to. See this and this entry for the GPL FAQ. If you have further questions about this, please open a new question. – Philipp Sep 3 '17 at 10:24
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    @Philipp Putting software on a webserver doesn't license it. Placing it under a license does. And you cannot license something under the GPL to only one person, and none of the entries in the GPL FAQ say that. And that can't be right. If it were right, say I was the only person who had a GPL license and I distributed the code to Jeff. How could Jeff distribute it since he doesn't have a GPL license? And I sure can't give him one since I'm not the author. The misconception is entirely on your side here. If code is under a GPL license, everyone has that license. – David Schwartz Sep 3 '17 at 23:20
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    @DavidSchwartz should we start a chat on this? Note that you wrote: "When you offer something under an MIT, BSD, or GPL license, that license automatically applies to anyone and everyone." I know of a commercial vendor that did relicense on a request to only one of their customers part of their code under an MIT license and part under a GPL license: this was not done publicly, but ONLY for code variants redistributed to that single customer. It still would apply to everyone else downstream receiving the code form the customer only IF they redistribute it. – Philippe Ombredanne Sep 8 '17 at 8:59

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