Obligations of the LGPL

gsxruk

Hi,

I'm no legal expert but the Qt licensing is starting to confuse me. Each time I update my operating system and download Qt again, the licensing seems to get more "highlighted".

I'd appreciate if somebody could help me decide if I'm good to use Qt under LGPL for a potential commercial application.

I had previously believed that as long as the application linked to Qt dynamically, it should be OK. The source code for Qt would also needs to be provided in some way and the LGPL license provided etc.

However, there are a few things I'm not sure of. When going through all the questions the website now asks before downloading Qt I don't understand the question "Do you want to legally protect your product from reverse engineering?". Why would it not be legally protected from reverse engineering while using Qt with LGPL? Or is this referencing just the Qt library part?

Also, it states one of the obligations is that "The user is allowed to change and re-link the library used in the application or device – including reverse engineering. With LGPLv3 it is explicitly stated that the user also needs to be able to run the re-linked binary, and that sufficient installation information must be provided.". Is this not provided due to the library being dynamically linked (i.e. so the Qt library files used by the application can be changed)? Or does this mean something else?

Thanks.

alex_malyu

@gsxruk said:

Is this not provided due to the library being dynamically linked

No, you might need details on toolchain (compiler ), Qt building options, etc.

gsxruk

Thanks for the reply.

So, if those details are provided along with information on where the Qt libraries would have to be installed for the application to use them, that would cover the re-linking requirement?

Thanks.

JKSH

@gsxruk said:

Thanks for the reply.

So, if those details are provided along with information on where the Qt libraries would have to be installed for the application to use them, that would cover the re-linking requirement?

That's what I, and many other users, think. Please note that we don't have legal authority, however. For more authoritative sources, see https://blog.qt.io/blog/2014/08/20/adding-lgpl-v3-to-qt/ :

"If you are not sure what license you should be using in your project, please consult a legal expert."

"Digia has opened an email address for specific questions about using Lgplv3 in your project. Please contact us via Qtlicensing@digia.com." (This was before the Qt Company was formed; I'm not sure what the new email address is).

gsxruk

@JKSH Thanks for your help.