Qt World Summit: Register Today!

About LGPL license question

  • Hi everybody:

    I developed an application using Qt,
    Now, I want encapsulate the dll and executable to make a install package, and release it (using LGPL).
    For release, I read some document about Qt license, like:

    1. http://www.qt.io/terms-conditions/
    2. http://www.qt.io/FAQ/
    3. http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html
    4. https://www.gnu.org/copyleft/lesser.html

    I have a question need help:
    In the install program what "license agreement content" necessity to show user? (user must accept it for continue setup)
    I don't know how to write license agreement file(license agreement content)? or any "ideal", "example", "google search key word".....can provide for me!

    sorry, it's very bad syntax...

  • Basicly you need to do is include some kind of notification that you are using
    Qt and that it is licensed under LGPL in your program. Easiest way to do this is
    simply to add a "About Qt" item to you applications Help or About menu and make
    it run void QMessageBox::aboutQt(QWidget * parent, const QString & title) .
    You could also add a qt-license.txt file to the installation directory so that the
    license is available for reading in offline too.

    Basically that gives the user all the information they need, but if one starts to nitpick,
    the LGPL license also says that you must also offer the users a way to download Qt
    source files from the same server your installer can be downloaded from, linking to
    Qt website won't be enough. Alternatively you could include the Qt source code in the
    installer itself, but that would be just ugly and install a lot of unneeded bloat.

    If you want to make your own program open source you can just select a open source
    license that you find fits best to you needs and ideals and show the contents of that
    license in your installer window, you should also mention that the program is using
    Qt that is licensed under LGPL after your own text.

    If you don't want to make your application open source then you just simply need to write
    your own license or search the internet for example and modify it to tell about your
    application instead. Then just include a notice about Qt at the end like for OSS license.

    This is how I understand things and I am no expert on this matter.

  • You're not actually required to offer a download.
    You're supposed to provide it on request, and you're allowed to receive payment for the effort of shipping a cd-rom for example.

    Dropbox uses a link in the settings, "Drobox Vx.x.x uses open source software".
    Apple has a separate webpage https://www.apple.com/opensource/
    Sitecom (from the routers) actually offers a download of the open source libs used.

    But, as long the parent project is still alive, a link to their website should suffice.
    You might even consider a donation...?

    Get someone specialized in software licenses for a definite answer for your situation.

  • Thanks Huulivoide and Jeroen3.
    I carefully read your reply and I study LGPL license and Qt license FAQ again.
    So I got some conclusions´╝Ü

    1. provide the Qt source code
    2. use dynamic link library
    3. notified the user: the application is used by LGPL license
    4. provide the LGPL licensed contents

Log in to reply