I'm developing an free and open source application that uses Qt. I'm not making any changes to Qt library itself. I wanted to know:
- On what license can I publish my application sources.
- On what license can I distribute app's executables (that are linked with Qt)
- Are there any other requirements that I need to fulfill in order to be compliant with Qt licenses?
Here's what I believe is the answer:
- I can publish my application sources on any license that I want (MIT for example).
- I need to distribute app's executables with Qt compliant licence (LGPL in that case) as the executable linked with Qt library is a derivative work of Qt library.
- I need to put Qt compliant license in the same package I distribute the executables with. Since I don't display any copyright notices of my own during the application execution, I don't need to put any Qt's copyright notices either. Additionally since I use plain Qt library without any modifications I don't need to distribute its source code as it's publicly available on their website.
I have also read Qt FAQ, but I think Qt's requirements are not 100% compliant with the LGPL itself. Those parts I have doubts about (this is part of "3.7. What are my obligations when using Qt under the LGPL?"):
You will need to deliver the complete source code of Qt (including all modifications you did or applied) to your users/customers. Alternatively you need to provide a written offer with instructions on how to get the source code. Please also note that this has to be under your control, so a link to the source code provided by the Qt Project or Qt Company is not sufficient.
I haven't seen anything in LGPL that could back up this claim (that a link to Qt source code from their website isn't enough).
The user of an application or device using LGPL licensed software has to be notified of their rights by providing a copy of the LGPL license to the end user and displaying a prominent notice about your usage of LGPL licensed software.
I understand this as apart from adding LGPL license to the package I use to distribute the app I need explicitly display proper notice to the end user in the application, while LGPL says:
If the work during execution displays copyright notices, you must include the copyright notice for the Library among them, as well as a reference directing the user to the copy of this License.
and my work doesn't display any copyright notices during the execution, so according to this there's no need to display Qt's copyright notice either.
I would be very grateful if someone competent could review my thinking.