I was hired to develop a custom Qt application for a customer, but I'm concerned about the licensing.

My software will not be publicly distributed and it is going to be used exclusively by this customer.

Do I need to disclose my source code for this customer, if I link my application with Qt libraries, such as QtCore and QWebKit that can be installed from a Linux distribution repository?

  • Read the Qt license. You should understand the answer to this question before even thinking about using the library to begin with. – whatsisname Mar 15 '17 at 19:19
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    Hi Fernando, questions which show no research effort get downvoted on this site and often closed. To me, it looks you did not even take the slightest effort to on inform yourself before. Please start here qt.io/licensing. – Doc Brown Mar 15 '17 at 19:38
  • On the Qt website there is no explicit comment about software that you create for a single customer. It don't, even, define what they consider commercial use. – Fernando Mar 15 '17 at 20:15

The GPL requires you to only provide source code whenever you provide binaries. You may opt to provide neither of these. If you provide the customer with the binaries, GPL requires you to distribute the source to the customer as well, but not to the whole world.

However, recent versions of QT are licensed using many licenses from which you can choose the one you use. The most relevant to you is probably LGPL 3.0. LGPL 3.0 requires you to distribute only the object code if using static linking. In your case, you do not need to even distribute the object code, as you are using libraries that can be installed from repositories. Presumably this means dynamic linking.

However, I am somewhat surprised that you do not want to provide the source code to the customer. If the application is developed specifically for this customer, usually it is considered good practice to provide the customer also with the source code.

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  • The main problem is that it's not me, but the organization that I'm working for. They don't disclose source code for their customers. Do you know if it is possible to give only binaries for customers in this case? – Fernando Mar 15 '17 at 19:30
  • As I said in the answer, it appears to be "YES" for LGPL 3.0. Check the license of the Qt version you're using; if LGPL 3.0 is an option, you can give only binaries. – juhist Mar 15 '17 at 20:18
  • However with LGPL 3.0, if I am providing binary to customer but I am not giving any option to him to use his own version of LGPL library, does it violate the term? – Shashwat Kumar Jan 11 '19 at 9:39

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