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I have a question concerning derivative works of GPL'ed software. Imagine the following situation: A company writes a software (A) using a library (B) which is released under the terms of the GPL. Now of course, software (A) has to be released under a compatible license to the GPL. But what about dual-licensing? If software (A) is released under two licenses, GPL and a commercial one, is this in violation with the terms of library (B)?

To rephrase the question, does the GPL force exclusivity for derivative works?

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  • if released, must be “licensed … to all third parties.”
    – pst
    Jan 20, 2012 at 22:25
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    Your premise is wrong. If there is no derivative work of (b) there is considerable legal disagreement as to the validity of the viral provisions of the GPL. And legal advice is off-topic here.
    – bmargulies
    Jan 20, 2012 at 22:25
  • @bmargulies: Licensing advice is on topic here, although if the situation becomes complex there's really no useful advice other than talking to a lawyer. Not that a lawyer could help the OP here; the definition of "derivative work" in the GPL is controversial and (last I looked) there was no case law in the US pertaining to this.
    – David Thornley
    Jan 23, 2012 at 19:21
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    It wasn't 'here' when I added that comment, was it?
    – bmargulies
    Jan 23, 2012 at 20:00

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Now of course, software (A) has to be released under a compatible license to the GPL. But what about dual-licensing?

Software A can be released under any number of licenses as long as they are all compatible GPL.

If software (A) is released under two licenses, GPL and a commercial one, is this in violation with the terms of library (B)?

No. It seems unlikely (though not impossible) to create a commercial license which is also compatible with GPL.

Understand that you may charge (on any account) while distributing the software under GPL is not an issue. But wrapping it under close source will remain definitely in-compatible to GPL.

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If you created a derived work of a lib you received under the GPL then your lib is GPL.

If you paid them for a commercial license then the derived work is under whatever the terms are for that license

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Does the GPL force exclusivity for derivative works?

Yes, but the key is the definition of derivative.

The license of library (B) only comes into play if you distribute library (B) with software (A). If you release your software (A) independently of library (B) you can do whatever you want with it (though I guess making the library optional would limit the fnctionality of the software when not compiled with the library).

As such, you could release software (A) under GPL, bundled with library (B).

You could also, since you are copyright holder over software (A), release it under whatever other licenses you prefer. But in those cases your customers would have to download library (B) and compile it into your software themselves.

A better solution overall though, would be to ask the copyright owners of library (B) to offer it with a dual licenses themselves. Offering Lesser GPL could encourage commercial support for developing the library and the option of a commercial license could bring in money to support the community in lieu of contributing code back to the project.

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