Single executable + LGPL



  • A while ago I contacted the author of 'Enigma Virtual Box' and asked him if it would be possible to pack files with his software into a single .exe, which will be automatically replaced when you add files of the same name to the executable path.
    This way, Qt dll's could be distributed in a single executable (with all other required files) and, theoretically, shouldn't violation the LGPL, because you can still swap the dll's as you please.
    Since neither I, nor the author of 'Enigma Virtual Box' have the possibility to discuss this matter with a lawyer, whether there's really no violation of the LGPL, I'd like to ask you (the community)!

    Is it okay to distibute a single executable under Qt's LGPL with this 'replacement feature' or would it still be a violation of the license? Any feedback is highly appreciated ;)


  • Lifetime Qt Champion

    Hi and welcome to devnet,

    Do you mean use an installer that would replace all .dlls on installation of a new version ?



  • @SGaist said in Single executable + LGPL:

    Hi and welcome to devnet,

    Do you mean use an installer that would replace all .dlls on installation of a new version ?

    Hello SGaist, thanks for your reply and the welcome!

    No, there is no installer involved! With 'Enigma Virtual Box' you can pack all your files needed for your executable to run, into a single .exe (e.g.: MyProgram.exe, Qt5Core.dll, Qt5Gui.dll, Qt5Widgets.dll and some images or icons -> MyProg.exe). Normally this would violate Qt's LGPL due to the fact, that the dll's can't be changed/swapped afterwards. But with the new feature I asked for, you are also able to copy a different version of the Qt-Dll's to the same directory as MyProg.exe and it runs with those local dll's instead of the (before) virtualized ones. Technically (and to my understanding) not a violation of the LGPL!? But again, I haven't spoken to a lawyer nor am I one and we (the author and I) sure don't want to upset the Qt devs by advertising a (free) product, that violates the license... That's why I'm asking here first ;)


  • Moderators

    @bbc-chi said in Single executable + LGPL:

    With 'Enigma Virtual Box' you can pack all your files needed for your executable to run, into a single .exe (e.g.: MyProgram.exe, Qt5Core.dll, Qt5Gui.dll, Qt5Widgets.dll and some images or icons -> MyProg.exe).

    This is an interesting concept. So, MyProg.exe is more like a container for MyProgram.exe and the DLLs.

    with the new feature I asked for, you are also able to copy a different version of the Qt-Dll's to the same directory as MyProg.exe and it runs with those local dll's instead of the (before) virtualized ones. Technically (and to my understanding) not a violation of the LGPL!?

    I think this feature fulfills your obligations to allow users to replace the Qt software in your application with their own verison.

    But again, I haven't spoken to a lawyer nor am I one and we (the author and I) sure don't want to upset the Qt devs by advertising a (free) product, that violates the license... That's why I'm asking here first ;)

    Be aware that this community (including myself) aren't lawyers and we don't often talk to lawyers either :)



  • @JKSH said in Single executable + LGPL:

    @bbc-chi said in Single executable + LGPL:

    With 'Enigma Virtual Box' you can pack all your files needed for your executable to run, into a single .exe (e.g.: MyProgram.exe, Qt5Core.dll, Qt5Gui.dll, Qt5Widgets.dll and some images or icons -> MyProg.exe).

    This is an interesting concept. So, MyProg.exe is more like a container for MyProgram.exe and the DLLs.

    Exactly! MyProg.exe contains all required files to run MyProgram.exe in a virtual environment. Hence the name 'Virtual Box' ;)

    with the new feature I asked for, you are also able to copy a different version of the Qt-Dll's to the same directory as MyProg.exe and it runs with those local dll's instead of the (before) virtualized ones. Technically (and to my understanding) not a violation of the LGPL!?

    I think this feature fulfills your obligations to allow users to replace the Qt software in your application with their own verison.

    I'd think so too... But who really understands all the 'License Agreements and Service Terms'?

    But again, I haven't spoken to a lawyer nor am I one and we (the author and I) sure don't want to upset the Qt devs by advertising a (free) product, that violates the license... That's why I'm asking here first ;)

    Be aware that this community (including myself) aren't lawyers and we don't often talk to lawyers either :)

    Is there anyone on this forum I could ask? You know... Better safe than sorry


  • Lifetime Qt Champion

    I'm not aware of any lawyer member. What you can do is ask the Free Software Fondation, they should be able to give you accurate advices.



  • @SGaist said in Single executable + LGPL:

    I'm not aware of any lawyer member. What you can do is ask the Free Software Foundation, they should be able to give you accurate advices.

    Thanks for the tip... I'll investigate ;)

    But, to be perfectly honest, I was hoping for a more in-house advice... sigh


  • Lifetime Qt Champion

    The only advice one can give regarding licenses when he's not himself a lawyer is: ask a lawyer.


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