Licensing



  • Hello,
    I wonder if i can use Qt Community Open Source version to develop a commercial product.

    The answer seems to be 'Yes', but i have to fulfill the license obligations for LGPL

    I can :
    Commercial Use
    Modify
    Distribute
    Place Warranty
    Use Patent Claims
    I can not :
    Sublicense
    Hold Liable
    I have to :
    Include Original
    State Changes
    Disclose Source
    Include License
    Include Copyright
    Include Install Instructions

    Can please someone confirm this ?
    then, If this correct (confirmed),
    how about i want to add OPCUA (it is commerial) in my application later ? Do i have to go commercial or i can compile and link QtOpcUa to my Qt my self and still keep free opensource version ?


  • Qt Champions 2018

    @LeLev I might be wrong, but Ithink OPC UA is GPLv3, not LGPL.



  • @aha_1980 sorry, i think i didn't phrase my question well.
    I wanted to know if i'm allowed to use Qt Community Open Source version to develop a commercial product, am I ?


  • Lifetime Qt Champion

    Hi,

    WARNING: I am not a lawyer

    Yes you can, no problem with that provided that you abide by the LGPL constraints (if using that license).

    Now, if you want to use QtOpcUA which is indeed Commercial/GPL licensed, then you have to either get a commercial license if you want to keep your software closed sources or you have to abide by the GPL license and provide your application sources on demand to whoever asks for it. Note that GPL doesn't forbid to sell software in any way.

    As always with that kind of question, better ask a competent lawyer.

    [edit: added missing lawyer warning SGaist]



  • @SGaist thank you very much



  • IANAL, if you want legal advice get a lawyer. If you want general perceptions about licensing that may not be accurate then read on.

    @LeLev said in Licensing:

    I can :
    Commercial Use

    Yes, for LGPL you can do commercial. Technically with GPL you can too, but that will change what you are required to distribute. But for simplicity stick with LGPL.

    Modify

    You may modify your own code as much as you want. However, if you modify Qt libraries AND distribute those modified libraries, you must provide source only for those libraries.

    Distribute

    Yes, you can distribute LGPL and GPL libraries as much as you want.

    Place Warranty

    ?

    Use Patent Claims

    ?

    I can not :
    Sublicense

    You cannot change the original license of the LGPL/GPL projects.

    Hold Liable

    ?

    I have to :
    Include Original

    For LGPL libraries you have to include/give access to the source for those libraries. This is easy as you can just point to Qt for access. If you made changes to the LGPL libraries then you must include those changes/give access.

    State Changes

    ?

    Disclose Source

    Same as include original.

    Include License

    Yes, I think.

    Include Copyright

    Same.

    Include Install Instructions

    Only if your nice.

    If you distribute projects with dynamic libraries that are LGPL then you only have to provide access to source code to the LGPL libraries if you made changes to them. You don't have to provide source for the code you write. If you distribute projects with GPL libraries in them then you have to provide access to the source code for the entire project. This is because GPL licensed code doesn't have the linking exception.

    With either LGPL or GPL you can create commercial projects. However, GPL projects will require you to provide your own source code be licensed under a GPL compatible license and provided to the end user. This may or may not fit your particular business model. For some companies its fits their model, others is does not. If distributing the source code with your project does not fit your business model then do not use GPL licensed code. Stick to LGPL, MIT, BSD, Apache, etc licensed libraries. These licenses allow you to license your own code under whatever license you want and does not require distribution.

    Also note, that not everything Qt provides is LGPL. You must pay attention to what is GPL vs LGPL. Fortunately the Qt documentation is very clear on what is GPL/LGPL. So read the docs carefully.

    Note, that to meet the requirements of LGPL with a library you need to stick with dynamic linking. If you need static linking you may need to consider a commercial license. Some platforms require the project to be statically linked. If you choose one of those platforms it may push you to a commercial license. I think iOS is one of those. Not 100% sure.

    There are probably better forums than this one for these kinds of questions.


  • Lifetime Qt Champion

    @fcarney said in Licensing:

    Note, that to meet the requirements of LGPL with a library you need to stick with dynamic linking. If you need static linking you may need to consider a commercial license. Some platforms require the project to be statically linked. If you choose one of those platforms it may push you to a commercial license. I think iOS is one of those. Not 100% sure.

    You don't need to stick to dynamic linking however you have to provide the built artefacts for your libraries/applications so that people can relink these to the version they want of a library. Since it's a none obvious procedure nor an easy situation to maintain, people usually stay with dynamic linking.



  • @fcarney Thank you very much for the details


 

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