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I understand that any work that is based on work licensed under GPL must also be released under GPL. However, it does not require contacting original authors about the fact that a derivative work has been, in fact, created.

I have a project for which source codes will be released. What I would like to do is keep the license open-source (GPL3) but get informed if someone uses those sources to create derivative work. I know this would be in general quite impractical for large projects because it would fill authors' inboxes quickly. However, I don't expect that there will be many derivative works (if any) as the source code will be published only on offline medium.

Is there a way to extend GPL to require this behavior?

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    Possible duplicate of Can the original author see other people's modifications?
    – curiousdannii
    May 10, 2018 at 15:40
  • The GPL has a provision that you can provide a "written offer" for source code. This means someone would in practice have to contact you for the source code. When that happens, you must provide it, but you would also know that they (may) be creating a derivative work.
    – Brandin
    May 10, 2018 at 15:43

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Requiring someone to do something on creating a derivative work is generally considered to make software non-free; this is the "desert island test":

Imagine a castaway on a desert island with a solar-powered computer. This would make it impossible to fulfill any requirement to make changes publicly available or to send patches to some particular place.

More specifically for the GNU GPL v3, adding any further restrictions to the software is forbidden by Section 10:

You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License.

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  • Interesting reasoning with those debian tests, thanks for bringing that up. Anyway I wasn't aware about the clause in GPL and it answers the question clearly.
    – Raven
    May 10, 2018 at 23:31
  • @Raven For a practical application of the desert island test, consider a developer living in a country whose national firewall allows access to the software, but not to the ability to contact the author.
    – apsillers ♦
    May 10, 2018 at 23:59
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    @Raven The "no further restrictions" applies to recipients of the license grant. As the licensor, you may impose whatever terms you choose (and the FSF has given permission to modify the GNU GPL as a basis for your own license), so you may make your own license, but it would be non-free and GPL-incompatible, not to mention annoying if the work gets many authors and requires a modifier to send many notifications (and really, annoying for many other cases, depending on the exact wording of the requirement).
    – apsillers ♦
    May 11, 2018 at 0:56
  • @Raven: What you can do is to let it be known that it would be very much appreciated if you are notified about derived works, without making that a part of the license.
    – Bart van Ingen Schenau
    May 11, 2018 at 7:13
  • So in that case it's also not allowed to ask questions about the GPL on opensource.stackexchange? because the GPL also is "Requiring someone to do something on creating a derivative work"
    – matthias_buehlmann
    Aug 15, 2020 at 16:33

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