June 1, 2010

Esdras Beleza Esdras Beleza
Lab Rat
22 posts

The same old topic: Licensing.

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Hi,

I need to prepare a lecture for my colleagues about Qt Development, and one of the topics is licensing. But it’s a very controversial topic, since the three Qt licenses make its licensing hard to understand. I tried to read Qt Licensing [qt.nokia.com]) a few times, but I’m still confused.

So, I’ll start with a some questions:

1) Can I develop and deploy closed-sourced commercial applications without buying a commercial license of Qt?

2) A more specific question, since the answer may be different: can I develop and deploy closed-sourced commercial applications without buying a commercial license of Qt, distributing it with the original Qt libraries, without any changes on it?

My personal projects are free and open sourced, but I need these questions answered so I could convince (or not…) some coworkers to use Qt on their commercial projects.

39 replies

June 1, 2010

aavit aavit
Lab Rat
6 posts

IANAL, but in my understanding: Yes & yes. You need to comply with the LGPL 2.1 though.

June 1, 2010

ucomesdag ucomesdag
Lab Rat
226 posts

To my understanding you must also make the source code available.

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Write “Qt”, not “QT” (QuickTime).

June 1, 2010

Esdras Beleza Esdras Beleza
Lab Rat
22 posts
ucomesdag wrote:
To my understanding you must also make the source code available.

Which source code?

June 2, 2010

Denis Kormalev Denis Kormalev
Lab Rat
1607 posts

Not a lawyer too, but AFAIK you can distribute your closed-source commercial software with or without original Qt libraries if you use LGPL. And you con’t need to provide source code by this license.
AFAIR there are some issues with static linking with Qt libraries.

June 2, 2010

aavit aavit
Lab Rat
6 posts

You do not need to distribute the application source code (ref. LGPL section 6) as long as the application is only dynamically linked to Qt (which is the ordinary case). Then the LGPL allows you to distribute your application under “the terms of your choice” (i.e. any license you like), provided that those terms “permit modification of the work [i.e., your application] for the customer’s on use and reverse engineering for debugging such modifications.”

If you modify Qt itself, then you must distribute the source code of your modified version of Qt if you want to distribute an application that uses it. You still do not have to distribute the source code of your application.

(Standard disclaimer: this is not official Nokia legal advice blah blah blah)

June 2, 2010

Jorj Jorj
Lab Rat
87 posts
aavit wrote:
“permit modification of the work [i.e., your application] for the customer’s on use and reverse engineering for debugging such modifications.”

To what extent is this required, do you just not sue them when they hack your app, or provide the ability to write plugins, or prpovide debug libraries (basically as good as source code, isn’t it?)

This is very interesting, I love Qt personally… But I always thought the licencing thing would stop me producing closed source apps or commercial programs…

June 2, 2010

aavit aavit
Lab Rat
6 posts
jorjpimm wrote:
To what extent is this required, do you just not sue them when they hack your app, or provide the ability to write plugins, or prpovide debug libraries (basically as good as source code, isn’t it?)

As I read it, the LGPL in this regard only places restrictions on the terms of the (optionally commercial, closed-source) license that you choose to distribute your application under. In effect, the LGPL says that that license may not contain things like “modifications or reverse-engineering is not allowed”.

The FSF may provide more in-depth on this: http://www.fsf.org/licensing/

jorjpimm wrote:
This is very interesting, I love Qt personally… But I always thought the licencing thing would stop me producing closed source apps or commercial programs…

While that might have been an issue earlier, while Qt was under Trolltech’s business model, it should not be now, after Nokia started releasing Qt under LGPL also (which happened about a year ago).

(Standard disclaimer applies)

June 2, 2010

Jorj Jorj
Lab Rat
87 posts

more open than i thought! Cool, however open source will still remain my distribution of choice i think.

June 2, 2010

mariusg mariusg
Ant Farmer
1091 posts

Have a look at this blog post for information about this directly from Qt legal:

http://blog.qt.nokia.com/2009/11/30/qt-making-the-right-licensing-decision/ [blog.qt.nokia.com]

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Project Manager - Qt Development Frameworks

June 3, 2010

Jorj Jorj
Lab Rat
87 posts

MariusG wrote:
Have a look at this blog post for information about this directly from Qt legal:

http://blog.qt.nokia.com/2009/11/30/qt-making-the-right-licensing-decision/ [blog.qt.nokia.com]

Has that page changed recently? Because I’m sure I have been on a page with the same title, and it used to be not so useful, but now looks very good.

June 3, 2010

mariusg mariusg
Ant Farmer
1091 posts

Apart from a small css update it’s the same as before.

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Project Manager - Qt Development Frameworks

June 3, 2010

ucomesdag ucomesdag
Lab Rat
226 posts

MariusG wrote:
Have a look at this blog post for information about this directly from Qt legal:

http://blog.qt.nokia.com/2009/11/30/qt-making-the-right-licensing-decision/ [blog.qt.nokia.com]

Thanks that made it all clear to me!

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Write “Qt”, not “QT” (QuickTime).

June 16, 2010

Stavros Filippidis Stavros Filippidis
Lab Rat
392 posts

Since comments at

http://blog.qt.nokia.com/2009/11/30/qt-making-the-right-licensing-decision/

are closed, I was wondering if I could have an answer at the following scenario/question:

If someone writes a closed-source Qt application for Windows based on the LGPL-licenced Qt framework, and if he/she doesn’t change the libraries, and if he/she linked dynamically with the dlls (Qt for Windows) then:

a) if he/she doesn’t provide the dlls but he/she only provides the exe
b) if he/she provides both the exe and the dlls

does he/she has to provide the (unchanged) source code of the dlls?

June 16, 2010

Denis Kormalev Denis Kormalev
Lab Rat
1607 posts

Stavros Filippidis, AFAIK in both cases you shouldn’t provide code.

June 16, 2010

Stavros Filippidis Stavros Filippidis
Lab Rat
392 posts

@*Denis Kormalev*: Just to clarify, I am NOT referring to the source code of the application, but to the source code of the Qt libraries (QtCore4.dll, QtGui4.dll, etc). In any case, I am not a lawyer, I am just have these questioned unanswered. :)

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