From reading this, I think there is some misunderstanding of software
licensing on Linux. There are a number of different licenses.
GPL - This is from the FSF. Linux itself (eg. the kernel) is licensed using
this as is most of the GNU utilities. The GPL does NOT prevent you from
selling your software. It does require you to make the sources available.
LGPL - Libraries and headers files use the LGPL. This allows you to develop
an application on Linux using libraries using this license, and that
application could be released as closed source, or proprietary.
There is also the Berkeley License, the MIT license, and many other
licenses. If you are using QT, you also have a license to deal with.
--
Jerry Feldman