How to publish Qt changes under LGPL?



  • We've developed a commercial Qt application with Qt under LGPL. We link dynamically. We also made a few changes to a couple of files in Qt to better suit our needs. I realize that according to LGPL, I must make those changes publicly available.

    My question is how is that done?

    Do I set a webpage on my domain with the modified source codes available for download?

    Do I distribute the modified source code in a folder on the client target machine after installation?

    Another way?

    I realize I asked a similar question before: http://qt-project.org/forums/viewthread/15367/

    however, the answer sent me to another thread that did not elaborate beyond "You have to publish it [your source code modifications]". My question remain: HOW? Website? With my installer onto all customer machines?


  • Moderators

    IANAL, but as I understand it, if you make changes just making the source publicly available in any form is sufficient, in that others can get to the code. (This could be just publishing a link on a web site, for instance.) I don't believe you have to install or push the code anywhere. As far as I know, in this context, publish just means to make publicly available. If I'm wrong, I imagine someone will point it out.



  • Including the source code with the binary, or providing a link where it can be downloaded are both acceptable as far as I know.
    See http://www.gnu.org/licenses/gpl-faq.html

    It's normal to include the source code on the disk for physical media distributions, and as a download for internet distributions.

    You don't have to install the source code on all user's machines, they just need to be able to get it if they want to.
    If your changes are generally applicable, please consider contributing them back to the Qt project though. (This is not required by LGPL)



  • Do I have to actively advertise that I made changes to Qt? How would users know about this page on my web server offering to download a change to Qt?



  • The license comes with no advertising requirements, but it must be possible for the user to understand the Free Software origins. A link in the about box pointing to a page where you publish your modifications should be enough.

    If the modifications are of general use, how about pushing them into Qt?


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