Is Linux UNIX?

You'll likely hear people say that Linux isn't UNIX at some point in your Linux career. And to some degree, they are correct, but not in the way that they likely mean. Linux is only a kernel, one piece of a UNIX operating system. But operating systems built on Linux are, by and large, UNIX - at least according to the most definitive possible source, Dennis Ritche, one of the creators of UNIX. Linux implements both the UNIX approach and ecosystem, as well as the UNIX interfaces. It is a UNIX, just as FreeBSD and others are. UNIX is both a standard and a trademark. But the two are not necessarily maintained together. The waters are a bit muddy here. But standard Linux systems, any that we will be discussing in this book, implement the UNIX standard (known as POSIX originally and now a super set of POSIXs, known as SUS). So, they are a UNIX variant or derivative, just as Dennis Ritchie said that they were way back in 1999. He said the same thing about the BSD...