LGPL license and 4 degree of freedom



  • Hi all.
    I'm working on a small software with Qt5 which control a small hardware by rs232 port.

    I read the LGPL obbligations.
    In particular the first degree of freedom is nebulous for me.

    It tells

    ... The freedom to run the program for any purpose...

    My software can work only if it is attached to the custom peripheral.
    How can I give the permission to use my software for any purpose if it can work on with my external hardware?

    Someone can explain me this matter?

    Best regards,
    MZ


  • Qt Champions 2016

    well you allow them to try.
    Even if we know it wont work.
    The point is users are granted the freedom to do it.

    Like I ask you , can I try with my hardware ?
    "Sure, but the protocol is different."



  • Ok, but in this case I need to give the protocol to use my hardware?
    I think no because the firmware of the hardware is not licensed under LGPL.


  • Qt Champions 2016

    well if purely in the hardware then not.

    Af far I as understand so far, if you dynamic link to Qt,
    you are not required to supply source code for your application.
    I could be wrong though.



  • Hi there,

    If your program is using Qt for commercial purpose and you haven't paid the license fee, then you are require to make it opensource. It doesn't matter whether you are linking it dynamically or statically to Qt libraries.

    Thanks,
    Anant Agrawal


  • Qt Champions 2016

    @AnantAgrawal
    hi
    Can you show me where you get that from ? as it dynamic linking is
    “work that uses the library" and you are not in that case required to give the source
    to "the work"

    https://forum.qt.io/topic/23549/licensing-confusion-with-qt5-solved/4



  • @AnantAgrawal said:

    If your program is using Qt for commercial purpose and you haven't paid the license fee, then you are require to make it opensource. It doesn't matter whether you are linking it dynamically or statically to Qt libraries.

    I think Anant meant: "if you use the LGPL version and modify Qt source code, then you have to pusblish your changes"


  • Qt Champions 2016

    @JulienMaille said:
    Ok. well that is correct.
    Scared me for a moment :)



  • Hi @mrjj & @JulienMaille,

    Thanks to both of you for your comments. I was clear on publishing my changes done in Qt sources if working with LGPL license.

    What I misunderstood was the licensing for applications developed using Qt. I was under the impression that an application used for proprietary usage (irrespective of linkage - dynamic or static) requires purchase of license.

    The truth is that if an application is developed using dynamic linkage with Qt libraries, then purchasing of license is not required. Please correct me if I still got it wrong.

    Regards,
    Anant Agrawal


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