Understanding the Implications of GNU Licenses
You have to pay a price for the bounty of Linux. To protect its developers and users, Linux is distributed under the GNU GPL (General Public License), which stipulates the distribution of the source code.
The GPL doesn’t mean, however, that you can’t write commercial software for Linux that you want to distribute (either for free or for a price) in binary form only. You can follow all the rules and still sell your Linux applications in binary form.
When writing applications for Linux, be aware of two licenses:
The GNU General Public License (GPL), which governs many Linux programs, including the Linux kernel and GCC
The GNU Library General Public License (LGPL), which covers many Linux libraries
Inform yourself well of these licenses and make sure you know how to meet their requirements. Don’t take anything here as legal advice. Instead, you should read the full text for these licenses in the text files on your Linux system, and then show these licenses to your legal counsel for a full interpretation and an assessment of their applicability to your business.
The newest version of the license is GPLv3 and a Quick Guide to it can be found at: GNU Operating System.