QT Open Source Licensing

[Netzschleicher]

Hello forum community,

some years ago I did something with Qt, but then nothing for a long time.

Now I am thinking about getting back into Qt. But I am not sure about the open source history of Qt.

I program as a hobby but I have my own GitHub account where I would like to make the one or the other program publicly available and offer ready to use binaries for download.

Am I allowed to do this with Qt, or are there any pitfalls? If I am allowed to do this, what do I have to pay attention to? So, e.g. License Infos in the
header and source files. I would definitely include the About-Qt dialog that is prefabricated by Qt.

Maybe someone can help me.

Greetings
Netzschleicher

[Netzschleicher]

Thank you very much,

i think i try to reactivate my Qt programming experiences.

Greetings
Netzschleicher

[sierdzio]

Most Qt modules are available under LGPL, all under GPL. As long as you fulfil the requirements of these licenses, you absolutely can publish on GitHub.

You can get a nice summary of both licenses here: https://www.tldrlegal.com/license/gnu-lesser-general-public-license-v3-lgpl-3 and https://www.tldrlegal.com/license/gnu-general-public-license-v3-gpl-3

[Netzschleicher]

Good morning,

thanks for the quick answer. I was / am a bit confused because I read in many places that Qt changes the license terms from time to time and thus makes the use for open source programs without commercial claim difficult or unusable.

[JKSH]

Hi, and welcome!

@Netzschleicher said in QT Open Source Licensing:

I read in many places that Qt changes the license terms from time to time

Where?

All current modules have retained the same licenses for years and years and years... Different modules may be released under different licenses, but they don't change licenses "from time to time".

[sierdzio]

@Netzschleicher said in QT Open Source Licensing:

Good morning,

thanks for the quick answer. I was / am a bit confused because I read in many places that Qt changes the license terms from time to time and thus makes the use for open source programs without commercial claim difficult or unusable.

It is true that Qt Company is very strongly promoting its business, and makes somewhat hard to find open source installer on its website, for example.

But Qt itself is still open source and there are no plans to change it. What's more, it cannot change because of a special agreement between Qt Company and KDE - if QtC ever decided to close Qt, code and copyright would automatically get transferred to KDE under BSD license.

[Netzschleicher]

Thank you very much,

i think i try to reactivate my Qt programming experiences.

Greetings
Netzschleicher

[dreiGeforce]

@sierdzio

Thanks for these links. I must say that in short it's hard to tell the difference between the two.

Can you please clarify about whether which of the two is preferred to stick to when it comes to self-use or internal use (in a company)?

Thanks

[SGaist]

@dreiGeforce LGPL is fine. GPL is really nice if you want to ensure that everybody can do whatever they want with the original code.

That said, for enterprise uses, it would be nice to have a license to help fund the maintenance cost of Qt. Emphasis on: it would be nice. There are also circonstances where a commercial license would be better beside the access to support.

Note that if some internal tool you wrote would become a product, their will be some paperwork to do as you cannot just transition from the GPL/LGPL to Commercial like that.

[sierdzio]

@dreiGeforce said in QT Open Source Licensing:

@sierdzio

Thanks for these links. I must say that in short it's hard to tell the difference between the two.

Can you please clarify about whether which of the two is preferred to stick to when it comes to self-use or internal use (in a company)?

The core difference is: if you use GPL Qt, then your code also has to be GPL.

With LGPL Qt, your code can use any license you want, you just need to make sure you follow LGPL rules (inform users that Qt is used, allow users to swap Qt version with their own, etc.).

Companies typically prefer LGPL, but it is really not up to me to decide :-) Both GPL and LGPL can be used in commercial setting, with both licenses software can be sold. With GPL it is not possible to stop users from copying/ forking/ selling your code, though.

[JKSH]

Note: The GPL and LGPL licenses are focussed on providing freedom for the software's users (as opposed to focussing on the software's developers).

The GPL guarantees more user freedom than the LGPL.