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Qt and closed source, commercial development



  • Hello!

    I'm a student that used Qt for an assignment given to me and some colleagues. We really liked using the framework, and were considering to use in a closed source and commercial project (which will possibly involve a custom embedded device as well). We read Qt's LGPL license though, and we're now not certain if this license is the right choice for us, considering the commercial nature of our project.

    More specifically, we would like to know if we can utilize Qt without purchasing the commercial license for said project we are considering to develop, provided we don't make any changes to the source code of Qt (by only using the libraries that are available to us), and dynamically linking these libraries (which we think is something we are already doing, since in our tests, the project we developed in our assignment required Qt to be installed in order for the application to run). Can we develop our program, given that we will do these things?

    Also, I had previously sent this message to Qt's support, but was only directed to this link, but we didn't find it to be very clear. About this "re-linking mechanism", does providing our client with the installer of the framework suffice in this regard? And, about "Make “open” consumer devices", does this have any effect on the use of our embedded device?

    I reckon this is a question that gets asked quite often, but we really need an up to date response, so I apologize for asking.

    Thank you for any answers.


  • Lifetime Qt Champion

    Hi,

    The only correct answer is: ask a lawyer (we are not on this forum).

    As for open device, AFAIK, it means that your device shall have a mechanism allowing its user to change the Qt version used there if they want to. It also applies to all librairies with similar licenses.

    Usually this means having a separate partition for all libraries in the same case that can be remounted in read/write mode.



  • Hello, thank you for your response.

    The device in question is an embedded Linux device with a package manager (Qt can be installed from said manager). I believe this means that obligation, about an open device, is fulfilled, would you think so?


  • Lifetime Qt Champion

    Will your users be able to access that package manager ?
    Will they be able to replace your Qt version by their own ?



  • @SGaist
    Yes, they will be able to do both things, once the project is delivered.


  • Lifetime Qt Champion

    Then it sounds good. You might want to ensure they can reset the device once they brick it by fiddling with it ;-)



  • You can use this app template:
    https://marketplace.qt.io/products/qt-lgpl-app-template
    Offers you a relink mechanism, also for embedded devices:
    you can release a redistributable project (your application inside a compiled static library, in a qt .pro project)
    and you must release your SDK (sysroot and compiler).
    If you use Static Qt, user can build his own Qt and rebuild your closed source application.