UNIX Expansion – History and Terminology

Most of these answers are far too late to the game, as the * usage was used on Usenet and elsewhere to refer to the multiplicity of Unixoid systems. This was significantly before "the suits" even knew what was happening in cyberspace and didn't understand it if they did.

I found a reference in the comp.risks archive dated May 1987 where the title

Concerning UN*X (in)security

was already so pedestrian as to warrant no explanation. By this time Xenix had been long on the market as were various "*ix" based variants which were decidedly "unix" but not "Unix".

That depends on what you mean by “Unix”, and by “Linux”.

• UNIX is a registered trade mark of The Open Group. The trade mark has had an eventful history, and it's not completely clear that it's not genericized due to the widespread usage of “Unix” refering to Unix-like systems (see below). Currently the Open Group grants use of the trade mark to any system that passes a Single UNIX certification. See also Why is there a * When There is Mention of Unix Throughout the Internet?.

• Unix is an operating system that was born in 1969 at Bell Labs. Various companies sold, and still sell, code derived from this original system, for example AIX, HP-UX, Solaris. See also Evolution of Operating systems from Unix.

• There are many systems that are Unix-like, in that they offer similar interfaces to programmers, users and administrators. The oldest production system is the Berkeley Software Distribution, which gradually evolved from Unix-based (i.e. containing code derived from the original implementation) to Unix-like (i.e. having a similar interface). There are many BSD-based or BSD-derived operating systems: FreeBSD, NetBSD, OpenBSD, Mac OS X, etc. Other examples include OSF/1 (now discontinued, it was a commercial Unix-like non-Unix-based system), Minix (originally a toy Unix-like operating system used as a teaching tool, now a production embedded Unix-like system), and most famously Linux.

• Strictly speaking, Linux is an operating system kernel that is designed like Unix's kernel.

• Linux is most commonly used as a name of Unix-like operating systems that use Linux as their kernel. As many of the tools outside the kernel are part of the GNU project, such systems are often known as GNU/Linux. All major Linux distributions consist of GNU/Linux and other software.

• There are Linux-based Unix-like systems that don't use many GNU tools, especially in the embedded world, but I don't think any of them does away with GNU development tools, in particular GCC.

• There are operating systems that have Linux as their kernel but are not Unix-like. The most well-known is Android, which doesn't have a Unix-like user experience (though you can install a Unix-like command line) or administrator experience or (mostly) programmer experience (“native” Android programs use an API that is completely different from Unix).