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Dear Red Hat: Are you dumb?
(www.jeffgeerling.com)
From Wikipedia, the free encyclopedia
Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
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I don't suppose they're modifying much of the GPL'd kernel necessarily. That's the part protected by GPL.
Their own actual distro is not exactly a modification of GPL software. And if they modify GPL software, they wouldn't have issues providing source code to that.