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I'm considering developing a project based on a modified version of some GPLv3 code. But, I need to use some proprietary library. This is a for-profit endeavour, in which I plan to sell the modified GPL code with the GPL license to a client and charge for the unitary closed-source cost of the proprietary library, but I cannot change the terms for the proprietary library. I can get license to share the headers or equivalents to them, but surely not to the library itself.

Is that okay? I believe I'd be violating the GPL license terms, but I'm not close-sourcing anything I have access to.

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  • The profit and selling stuff is not relevant. GPL allows these. However there are other reasons that you can not do it. See below.
    – ctrl-alt-delor
    Sep 24 '20 at 21:22
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Is that okay?

Almost certainly not. GPLv3 says in s5c that if you convey (distribute, for the purposes of this answer) modified versions of the original GPLv3 code (which includes distributing larger works incorporating the GPLv3 code)

You must license the entire work, as a whole, under this License to anyone who comes into possession of a copy

Some people make an argument that linking a library into code doesn't create a single work for copyright purposes, but I'm not one of them, and I certainly wouldn't bet a business on being able to do it.

I believe I'd be violating the GPL license terms, but I'm not close-sourcing anything I have access to.

I agree, but the first part of that sentence matters, and the second doesn't. As GPLv3 s12 puts it so eloquently:

If you cannot convey a covered work so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not convey it at all

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    And maybe to add: that is the whole point of choosing this copyleft license. Would the authors have wanted to allow the described scenario, they'd have chosen MIT or BSD or similar
    – planetmaker
    Sep 24 '20 at 6:15
  • The linking argument depends on the dependencies (not on static vs dynamic vs …). If the modified GPL depends on an incompatibly licenced work, then it is a GPL violation.
    – ctrl-alt-delor
    Sep 24 '20 at 21:20
  • @ctrl-alt-delor I'm not saying I disagree, but I will note that I made no mention of static vs. dynamic linking.
    – MadHatter ♦
    Sep 25 '20 at 5:57
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    @I agree totally with your answer, and comment. I was just pointing out one reason for the disagreement that you mentioned.
    – ctrl-alt-delor
    Sep 25 '20 at 7:59
  • @ctrl-alt-delor thank you for the clarification, for which I am grateful!
    – MadHatter ♦
    Sep 25 '20 at 8:00

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