The use and distribution of open source and free software is subject to a few well-known and widely advertised licenses, as we discussed in Chapter 1. There are, nevertheless, some issues surrounding Linux’s licensing that keep resurfacing and seem to cause confusion. These uncertainties revolve around the fact that the Linux kernel is itself distributed under the terms of the GNU GPL.
Over time, Linus Torvalds and other kernel developers have helped shed some light on the limits and reaches of the kernel’s licensing. This appendix presents some of the messages published by Linus and other kernel developers regarding three aspects of the kernel’s licensing: the use of non-GPL applications, the use of binary-only modules, and the general licensing issues surrounding the kernel’s source code.
To avoid any confusion regarding the status of applications running on top of the Linux kernel, Linus Torvalds added the following preamble to the kernel’s license:
NOTE! This copyright does *not* cover user programs that use kernel services by normal system calls - this is merely considered normal use of the kernel, and does *not* fall under the heading of "derived work". Also note that the GPL below is copyrighted by the Free Software Foundation, but the instance of code that it refers to (the Linux kernel) is copyrighted by me and others who actually wrote it. Also note that the only valid version ...