QT Commercial vs Open Source
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Qt will always tell you that it is safest to get the commercial license. There are a few things in the LGPL (especially in back in version 2 previously used by Qt) that have never been fought in court (for any software or library). This is where some uncertainty comes from. And also Qt wants to make money, so they will always tell you to buy the commercial license.
However, I am still unsure where the 3 years come from. This is not stated anywhere in the LGPL v3. The obligations that the LGPL states are:
- that you keep a copy of the source code (Qt in this case) that you can provide your clients with (you have to have a copy; it is not sufficient that there is an official download page)
- that you provide your client with everything he needs to relink your software
The second point is easily achieved by dynamically linking to Qt (i.e. DLLs). In theory (though this has never been legally tested), you can also statically link with Qt as long as you provide (upon request) the object files of your own software (and in special cases the linker as well) so that your client could relink your object files with a different Qt version. If you comply with this the Qt company can't force you into buying the commercial license.
I would assume that you need to provide the source code of Qt for the versions of the software you are still distributing. Though I am not a lawyer and so I don't know for sure. Keeping the source of Qt for another 3 years certainly helps legally, but as I said I can't find it in the official license itself.
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Qt will always tell you that it is safest to get the commercial license. There are a few things in the LGPL (especially in back in version 2 previously used by Qt) that have never been fought in court (for any software or library). This is where some uncertainty comes from. And also Qt wants to make money, so they will always tell you to buy the commercial license.
However, I am still unsure where the 3 years come from. This is not stated anywhere in the LGPL v3. The obligations that the LGPL states are:
- that you keep a copy of the source code (Qt in this case) that you can provide your clients with (you have to have a copy; it is not sufficient that there is an official download page)
- that you provide your client with everything he needs to relink your software
The second point is easily achieved by dynamically linking to Qt (i.e. DLLs). In theory (though this has never been legally tested), you can also statically link with Qt as long as you provide (upon request) the object files of your own software (and in special cases the linker as well) so that your client could relink your object files with a different Qt version. If you comply with this the Qt company can't force you into buying the commercial license.
I would assume that you need to provide the source code of Qt for the versions of the software you are still distributing. Though I am not a lawyer and so I don't know for sure. Keeping the source of Qt for another 3 years certainly helps legally, but as I said I can't find it in the official license itself.
@SimonSchroeder said in QT Commercial vs Open Source:
Qt will always tell you that it is safest to get the commercial license.
I would agree with this. Not that I wish to knock them, they are here to make money.
However, I am still unsure where the 3 years come from. This is not stated anywhere in the LGPL v3.
You will see I asked this earlier above, because I did not know about it. However, the link given --- https://tldrlegal.com/license/gnu-lesser-general-public-license-v3-(lgpl-3), go to the rightmost Must column, click on the 3rd item down, Disclose Source, it expands to show
If you distribute this library in an executable, you must make the source available for 3 years.
I took this to be some official LGPL document when I was referred to it by others above. I now realise it is just some guy's TL;DR. Hence why I questioned where the OP got his screenshot from. However, I also encounter in https://www.oreilly.com/library/view/understanding-open-source/0596005814/ch03.html
This is the most favored way to make source code available. It requires no additional effort from the distributee and is not time-limited. This is the best way to comply with Section 3 for all but the largest programs.
b) Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,so I assume it is indeed somewhere in LGPL?
But I must admit I am having trouble locating that quoted statement in the actual LGPL. Don't know which version/what source it was taken from....
Meanwhile, I happenstanced across https://www.slideshare.net/BurkhardStubert/using-qt-under-lgplv3. It has 37-page slideshow of what this guy had to say. I don't know/advocate whether what he says is true, but it might be worth a read through as it's aimed specifically at Qt.
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@SimonSchroeder said in QT Commercial vs Open Source:
Qt will always tell you that it is safest to get the commercial license.
I would agree with this. Not that I wish to knock them, they are here to make money.
However, I am still unsure where the 3 years come from. This is not stated anywhere in the LGPL v3.
You will see I asked this earlier above, because I did not know about it. However, the link given --- https://tldrlegal.com/license/gnu-lesser-general-public-license-v3-(lgpl-3), go to the rightmost Must column, click on the 3rd item down, Disclose Source, it expands to show
If you distribute this library in an executable, you must make the source available for 3 years.
I took this to be some official LGPL document when I was referred to it by others above. I now realise it is just some guy's TL;DR. Hence why I questioned where the OP got his screenshot from. However, I also encounter in https://www.oreilly.com/library/view/understanding-open-source/0596005814/ch03.html
This is the most favored way to make source code available. It requires no additional effort from the distributee and is not time-limited. This is the best way to comply with Section 3 for all but the largest programs.
b) Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,so I assume it is indeed somewhere in LGPL?
But I must admit I am having trouble locating that quoted statement in the actual LGPL. Don't know which version/what source it was taken from....
Meanwhile, I happenstanced across https://www.slideshare.net/BurkhardStubert/using-qt-under-lgplv3. It has 37-page slideshow of what this guy had to say. I don't know/advocate whether what he says is true, but it might be worth a read through as it's aimed specifically at Qt.
@JonB said in QT Commercial vs Open Source:
so I assume it is indeed somewhere in LGPL?
I can't see anything like "3 years" in LGPLv3. So, no idea from where this 3 comes.
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@JonB said in QT Commercial vs Open Source:
so I assume it is indeed somewhere in LGPL?
I can't see anything like "3 years" in LGPLv3. So, no idea from where this 3 comes.
@jsulm
Which is why I originally asked that at https://forum.qt.io/topic/111380/qt-commercial-vs-open-source/6 above!So far I have found the referenced picture plus one other source which mention the "3 years", but not much else.
I am having trouble locating the official, full LGPL text. Not summaries, explanations or opinions! Would you be kind enough to paste the exact link for whatever the official text is?
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@jsulm
Which is why I originally asked that at https://forum.qt.io/topic/111380/qt-commercial-vs-open-source/6 above!So far I have found the referenced picture plus one other source which mention the "3 years", but not much else.
I am having trouble locating the official, full LGPL text. Not summaries, explanations or opinions! Would you be kind enough to paste the exact link for whatever the official text is?
@JonB said in QT Commercial vs Open Source:
@jsulm
Which is why I originally asked that at https://forum.qt.io/topic/111380/qt-commercial-vs-open-source/6 above!So far I have found the referenced picture plus one other source which mention the "3 years", but not much else.
I am having trouble locating the official, full LGPL text. Not summaries, explanations or opinions! Would you be kind enough to paste the exact link for whatever the official text is?
This is the official text: https://www.gnu.org/licenses/lgpl-3.0.en.html
(Z(:^
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@JonB said in QT Commercial vs Open Source:
@jsulm
Which is why I originally asked that at https://forum.qt.io/topic/111380/qt-commercial-vs-open-source/6 above!So far I have found the referenced picture plus one other source which mention the "3 years", but not much else.
I am having trouble locating the official, full LGPL text. Not summaries, explanations or opinions! Would you be kind enough to paste the exact link for whatever the official text is?
This is the official text: https://www.gnu.org/licenses/lgpl-3.0.en.html
@sierdzio
Thank you. Yep, I had looked at that, but I thought it was way too short to be the whole text!? I recalled it was longer than that :)If that is the case, there is indeed no mention of "3 years", as I originally suspected :) This is the danger of using third-party, possibly out-of-date, summaries!
STOPPRESS Ah ha! It was in LGPLv2! See https://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html, search for
years:) It was also longer than v3 :) -
@sierdzio
Thank you. Yep, I had looked at that, but I thought it was way too short to be the whole text!? I recalled it was longer than that :)If that is the case, there is indeed no mention of "3 years", as I originally suspected :) This is the danger of using third-party, possibly out-of-date, summaries!
STOPPRESS Ah ha! It was in LGPLv2! See https://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html, search for
years:) It was also longer than v3 :)@JonB said in QT Commercial vs Open Source:
@sierdzio
Thank you. Yep, I had looked at that, but I thought it was way too short to be the whole text!? I recalled it was longer than that :)If that is the case, there is indeed no mention of "3 years", as I originally suspected :) This is the danger of using third-party, possibly out-of-date, summaries!
That's because LGPLv3 is based on GPLv3. There, 3 years are mentioned (https://www.gnu.org/licenses/gpl-3.0.html).
LGPL text only states that it modifies GPLv3 and is not a standalone license.
(Z(:^
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@JonB said in QT Commercial vs Open Source:
@sierdzio
Thank you. Yep, I had looked at that, but I thought it was way too short to be the whole text!? I recalled it was longer than that :)If that is the case, there is indeed no mention of "3 years", as I originally suspected :) This is the danger of using third-party, possibly out-of-date, summaries!
That's because LGPLv3 is based on GPLv3. There, 3 years are mentioned (https://www.gnu.org/licenses/gpl-3.0.html).
LGPL text only states that it modifies GPLv3 and is not a standalone license.
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@sierdzio
Your latest crossed with my post above where "three years" is indeed mentioned in LGPLv2. Are you saying that this still applies in v3, because we have to take that from GPLv3?@JonB said in QT Commercial vs Open Source:
@sierdzio
Your latest crossed with my post above where "three years" is indeed mentioned in LGPLv2. Are you saying that this still applies in v3, because we have to take that from GPLv3?I think so.
Just my musings on why it is there on TL;DR site, I have no idea if it is right.
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Yes, the LGPL v3 is based on the GPL v3 and only extends on that. This means you need to take the instructions for distributing source code from the GPL. You should understand, that there are different options, though:
a) just ship the Qt source code with your software
b) written offer to provide the Qt source code for at least three years or your support period (whatever is longer)
d) provide your software as download (either free or paid) and also the Qt source code as download from the same place (free of charge)These are picked from section 6 of the GPL v3. You see, that you have different options. Though the first might not be really feasible if your software is not at least 1GB in size (as the Qt source is quite large).
