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I'm using Qt Open Source, not selling the software, and need to keep source code hidden.



  • Hello,
    I have a little question about Qt GPL / GNU licenses. The problem I'm talking about is about a software application, where people must log into to a server somewhere on the web to be able to use. Meaning the program itself is free to download but to log in, users subscribe to a plan. This is handled by the server, on the web, where it is possible for people to register a subscription. Qt licenses ( which I want to use), are open source and I am therefore wondering if it is required by developers to share the source code of such use case.

    Thank you in advance===,

    Mikolaj


  • Lifetime Qt Champion

    Hi and welcome to devnet,

    See the Developing with LGPL part of the Qt Licensing Terms.


  • Lifetime Qt Champion

    @mikoo1991 Just to add to @SGaist, some Qt modules are not LGPL licenced (like QtCharts, which is licensed GPLv3).

    If you want to use them, you have to respect the GPL.



  • On the server you can have open source software (example GPL) and you do not have to show code to anybody because it executes on your machine.
    However the client application must be on LGPL license or GPL.
    What it means, when you want to have closed sources you must use Qt's dynamic libraries and you can close your code except GPL modules such as QtCharts and some QtVirtualkeyboard and parts using it.
    Code parts using some GPL modules must stay open to view and you have to show it on request when somebody ask you, for example sending email and then sending back file with GPL parts... or just put it on homepage or github...


  • Lifetime Qt Champion

    @BINALECTRUM there's something very wrong here: if you use a GPL dependency in your application, then all of your application goes GPL.


  • Moderators

    @BINALECTRUM That sounds like attempts to bypass GPL licensing and would most definitely get you in trouble.

    What it means, when you want to have closed sources you must use Qt's dynamic libraries and you can close your code except GPL modules such as QtCharts and some QtVirtualkeyboard and parts using it.

    Like @SGaist said it doesn't work like this. If you use GPL then you have to GPL your entire application. Not just the parts that use the GPL'd code. If you want closed source never use any GPL'd piece of code, it's pretty much impossible to comply with the GPL license with closed source software.

    Code parts using some GPL modules must stay open to view and you have to show it on request when somebody ask you, for example sending email and then sending back file with GPL parts... or just put it on homepage or github...

    Doesn't work like this at all. If you've done this in previous projects I'd highly recommend you hire a lawyer to interpret the GPL for you before you get caught and end up owing tons of money.

    On the server you can have open source software (example GPL) and you do not have to show code to anybody because it executes on your machine.

    This part is true since you are not actually distributing the product.

    Disclaimer: I am not a lawyer so while I'm pretty sure my understanding of the GPL is closer than @BINALECTRUM's, don't take this as legal advice, it may not hold up in court. ;)


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