[SOLVED]Freely distribute the Qt shared libraries (DLLs)?

Loaden · wrote on 15 Dec 2010, 00:41

Hi, all!
I've developed an application using the LGPL version of Qt. I've went over the LGPL license (http://www.gnu.org/licenses/lgpl-2.1.html), but am looking for a little clarification on some things.

I've used the Qt library without any modification, and the executable that will be shipped will be built with MSVC on Windows. The application will be dynamically linked to the Qt library. The source code of the application is proprietary.

Now, when I ship my application, I would need to include the Qt DLLs:

QtCore4.dll
QtGui4.dll
...
My understanding of the license is that I can freely distribute these DLLs, and only need to provide a copy of the LGPL license and a location (i.e., qt.nokia.com) to download the source code of the library from. Is this Correct?

Can I keep my application's source code proprietary, and freely distribute the Qt shared libraries (DLLs)?
Any help are welcome.
Thanks!!

anselmolsm · wrote on 15 Dec 2010, 03:46

Yes, you are correct. LGPL allows you to keep the source code of your application closed.

Loaden · wrote on 15 Dec 2010, 04:25

Thanks for reply!
The key point is: Can I freely distribute the Qt shared libraries (DLLs)?

mbroadst · wrote on 15 Dec 2010, 07:07

Yes, you can.

stukdev · wrote on 15 Dec 2010, 08:41

Yes, you can. And if i understand i have to provide a way to update the library if the user want this, right?

dangelog · wrote on 15 Dec 2010, 08:50

... which you already do by using dynamic linking: the user will just have to drop in the replacements.

stukdev · wrote on 15 Dec 2010, 08:52

Yes, but some user don't know this simple procedure and i have to write a minimal guide for this.
User != technician :P

[quote author="peppe" date="1292403048"]... which you already do by using dynamic linking: the user will just have to drop in the replacements.[/quote]

? This user is from outside of this forum · wrote on 15 Dec 2010, 09:41

hi loaden, do check this out: "http://blog.qt.nokia.com/2009/11/30/qt-making-the-right-licensing-decision/":http://blog.qt.nokia.com/2009/11/30/qt-making-the-right-licensing-decision/

andre · wrote on 15 Dec 2010, 10:24

[quote author="stuk" date="1292403168"]Yes, but some user don't know this simple procedure and i have to write a minimal guide for this.
User != technician :P

[quote author="peppe" date="1292403048"]... which you already do by using dynamic linking: the user will just have to drop in the replacements.[/quote]

[/quote]
As far as I know, the LGPL does not require you to explain how to do it. Just to make it possible to do so. I don't think writing a manual that states that you can drop in newer versions of the Qt library files is needed.

dangelog · wrote on 15 Dec 2010, 10:35

[quote author="stuk" date="1292403168"]Yes, but some user don't know this simple procedure and i have to write a minimal guide for this.
User != technician :P

[quote author="peppe" date="1292403048"]... which you already do by using dynamic linking: the user will just have to drop in the replacements.[/quote]
[/quote]

The LGPL doesn't require you to make your users smarter :-)

anselmolsm · wrote on 15 Dec 2010, 11:23

This 'allow updates' requirement is a way to guarantee your proprietary application does not depend on modifications you did in the library - it must be possible for the software to be linked with a newer version of the LGPL library (Qt, in this case :-P), not only to your Qt version. So, if you modify Qt (what is not you case, as you said), to respect LGPL you must submit the changes upstream.

I'm not a lawyer [1], please correct me if I'm wrong

[1] In 100% of the license discussions, someone must say this sentence, at least once =P

Loaden · wrote on 15 Dec 2010, 23:48

Thanks a lot!!

dangelog · wrote on 15 Dec 2010, 23:56

[quote author="anselmolsm" date="1292412214"]I'm not a lawyer [1], please correct me if I'm wrong

[1] In 100% of the license discussions, someone must say this sentence, at least once =P[/quote]

You're absolutely right. Was thinking if this should be some kind of FAQ: "Never ever ask for legal advice on forums, mailing lists, IRC and whatsoever. Consult an IT lawyer." (?)

goetz · wrote on 16 Dec 2010, 09:40

[quote author="peppe" date="1292457362"]You're absolutely right. Was thinking if this should be some kind of FAQ: "Never ever ask for legal advice on forums, mailing lists, IRC and whatsoever. Consult an IT lawyer." (?)
[/quote]

That might not help either. If you ask three of these guys you will get four opinions....

dangelog · wrote on 16 Dec 2010, 09:59

[quote author="Volker" date="1292492418"][quote author="peppe" date="1292457362"]You're absolutely right. Was thinking if this should be some kind of FAQ: "Never ever ask for legal advice on forums, mailing lists, IRC and whatsoever. Consult an IT lawyer." (?)
[/quote]

That might not help either. If you ask three of these guys you will get four opinions....[/quote]

Haha, ok, point taken, but at least they're supposed to know the matter and you sign agreements with them, whilst on forums you have no guarantees whatsoever.

goetz · wrote on 16 Dec 2010, 10:09

[quote author="peppe" date="1292493548]Haha, ok, point taken, but at least they're supposed to know the matter and you sign agreements with them, whilst on forums you have no guarantees whatsoever.[/quote]

That's true. It's in most cases better to ask a specialized lawyer than a forum with all that "I believe that..." answers.

giesbert · wrote on 16 Dec 2010, 10:16

But if you ask 3 lawyers, you perhaps get also 4 answers.
Perhaps the Trolls can make a definite statement? That could then also be put to FAQ?

Loaden · wrote on 20 Dec 2010, 14:52

Hi, All, Another question that is can i distribute all files (e.g. my apps, Qt DLLs) use one package (e.g. one NSIS install package, or one zip/7z/tar.gz package) ?
Many thanks!

andre · wrote on 20 Dec 2010, 15:21

Sure you can*!

*) Opinion of a non-lawer.

Loaden · wrote on 29 Dec 2010, 09:22

Change state to SOLVED.
Thanks all!