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Qt License query



  • Hello,
    We are trying to customize wireshark (hence will be modifying wireshark source code). Wireshark requires Qt installation for its development environment. Because of wireshark's GPL v2 license we will publish modified source to the community. but we might be charging our customer for the customized wireshark.
    Do we as a company, need to buy Qt to build wireshark development environment in this case? Or we can use the free Qt version as being used by wireshark community?

    Thanks,
    Amit


  • Lifetime Qt Champion

    Hi and welcome to devnet,

    warning I am not a lawyer

    AFAIK, you don't need to buy a commercial licence since you are going to work and publish properly your changes to a GPL project.



  • Thank you SGaist for the response. I have edited my query above with a critical point I missed out in initial posting.


  • Moderators

    @msg2arc said in Qt License query:

    Thank you SGaist for the response. I have edited my query above with a critical point I missed out in initial posting.

    I don't know what is that critical point you added, but @SGaist's answer is still correct for the text I see currently.

    I suspect this is the crucial point:

    but we might be charging our customer for the customized wireshark.

    No problem there. GPL does not prohibit reselling. https://www.gnu.org/licenses/gpl-faq.html#DoesTheGPLAllowMoney



  • Thank you so much for reply.
    I have one more question. In case we decide to host the custom wireshark internally and sell it to customer (where we would offer to distribute wireshark custom source as well to end customer complying to distributing license nature of GPLv2), in this case we must buy Qt licenses?

    If yes, what set of licenses should be bought for wireshark development and distribution?

    Regards,
    Amit


  • Moderators

    You don't need to buy Qt license in this case. You have really asked the same question as before, just using different words ;-)



  • Thank you.
    It was a different question in the sense that we will host wireshark source code internal to organization (not on github in open source way). Does that still enable us to use Qt for free? I think Qt is not only used for build, it also implements wireshark UI and hence will get distributed with wireshark.

    *we intend to distribute wireshark soure code to end customer as per GPLv2.



  • @msg2arc said in Qt License query:

    we intend to distribute wireshark soure code to end customer as per GPLv2.

    I guess you need to be prepared to distribute the source code of "changed" wireshark to anyone who ask for it, not just your customer. But I'm not a lawyer.



  • I realise that your question is a few months old. However I'd like to clarify and answer for you or anyone who may come across this in a google search as I did.

    Your question is basically 4 questions:

    1) Can one use the (largely) LGPL OpenSource QT to edit GPLv2 Source Code?
    A. Yes. If you distribute a binary, as per LGPL you must provide a way for the recipient to re-link the binary with their own or different versions of the libraries provided by QT. GPLv2 code CAN be linked to an LGPL library. In this sense they are perfectly compatible..

    2) Do you need to distribute any source code?
    A. Yes. You must re-distribute your modified GPLv2 Source. It doesn't have to be GitHub, but anyone who gets a binary from you must be made aware of where to get sources.

    3) Does using a commercial version of QT release you from your obligation?
    A. Yes and No.

    No, because GPLv2 does not allow any modifications to be held under any other license but GPLv2, so you are obligated to follow those guidelines irrespective.

    Yes, because you no longer need to keep up with QT's LGPL guidelines, you can choose to not distribute any changes you make to a QT Library and/or not provide a relinking mechanism.

    4) Can you charge for your effort?
    A. Yes. Whether you go OpenSource or Commercial you can charge your client.


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