[Qt-interest] Question regarding QT license

[Konrad Rosenbaum]

Hi,

[Disclaimer: IANAL]

On Monday 10 August 2009, Alex wrote:
> Can anyone explain me the question regarding the QT LGPL license?
>
> My Goal (My boss's goal, actually):
> Develop a proprietary commercial application based on QT framework with
> LGPL version under Linux.
>
> My Questions:
>
>    1. All binary executable program, i.e. all .exe file, can't static
> linked to QT's libraries, right?

Sure they can, but then you have to distribute the program in a form that 
allows the customer to re-link it against a different (compatible) version 
of Qt.

In other words: in theory static linking is allowed, in practice it does not 
make sense.

>    2. If the application is linked to QT's shared libraries, can the
>    application pack all necessary QT's shared libraries into its
> installer to simplify the application's deployment? Or I have to tell my
> customers to install QT first? The latter seems not make sense to my
> customers.

You can include Qt.

> 3. Do I need putting a QT license (LGPL v2.1?) file in 
> somewhere to the application?

You have to tell your customers about Qts license somewhere (eg. during 
installation give them a hint where to find the file with the full LGPL).

And you have to give your customers access to EXACTLY the same version of Qt 
sources that you used to create the DLLs you distributed with your program: 
either offer them (visibly!) to send them the sources or display a URL for 
the sources somewhere (eg. on a page in your manual or during installation) 
or just deliver the sources on the same media that you deliver your product 
on (if you do a CD/DVD based distribution, the latter is usually less 
hassle).

Another hint for Linux: almost all major Linux distributions ship with 
Qt4/LGPL prepackaged. If you happen to create a distribution specific 
package anyway, just link against that package and leave all that hassle to 
the distributor. Eg. doing this for Debian and Ubuntu (they can share the 
same package config) takes about a day including quite a bit of 
experimentation.


	Konrad
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