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LGPL and commercially with closed source



  • Hi,

    generally, what I (think to) know is. I can use Qt-LGPL in my closed-source-non-LGPL commercial application, if I link dynamically to Ot (i.e., using Qt DLLs).

    What puzzles me from https://www.gnu.org/licenses/gpl-faq.html#LGPLStaticVsDynamic is this statement:

    (2) If you dynamically link against an LGPLed library already present on the user's computer, you need not convey the library's source.
    On the other hand, if you yourself convey the executable LGPLed library along with your application, whether linked with statically or dynamically, you must also convey the library's sources, in one of the ways for which the LGPL provides.
    

    This seems to imply that, since I can never be sure if my customer has Qt sources, that I need to provide Qt sources to the customer. This does not seem to make any sense, though. I can say in my software that I use Qt version x.y, so that they can download the sources, if they want to. Why should I bloat my package by including all the Qt source?

    However, does LGPL enforce to include Qt's source? From the quote, it certainly seems so...

    Thanks!!


  • Lifetime Qt Champion

    @IceMichael I think it is enough to provide Qt source code when a user asks for it, not in your installation package. But I'm not a lawyer.


  • Moderators

    @jsulm said in LGPL and commercially with closed source:

    @IceMichael I think it is enough to provide Qt source code when a user asks for it, not in your installation package. But I'm not a lawyer.

    I agree with @jsulm (but I'm not a lawyer either)

    See also GNU's website: https://www.gnu.org/licenses/gpl-faq.en.html#WhatDoesWrittenOfferValid

    If you choose to provide source through a written offer, then anybody who requests the source from you is entitled to receive it.

    If you commercially distribute binaries not accompanied with source code, the GPL says you must provide a written offer to distribute the source code later. When users non-commercially redistribute the binaries they received from you, they must pass along a copy of this written offer. This means that people who did not get the binaries directly from you can still receive copies of the source code, along with the written offer.

    The reason we require the offer to be valid for any third party is so that people who receive the binaries indirectly in that way can order the source code from you.



  • Have a look at a recent discussion in this forum: https://forum.qt.io/topic/111380/qt-commercial-vs-open-source

    You need to have the Qt sources somewhere on your computers to be able to provide them to your customer/users. It is not sufficient to link to Qt's own download of the source.

    If you have your software as a download somewhere it is sufficient to provide a download link (to Qt sources on your own server) as well.

    Another way is to provide a written offer valid for at least three years with your software that you will provide Qt's source upon request.

    You can also provide Qt's source with your installer. But as you already said, that is total overkill.




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