What is the difference between Linux and Unix?
To put it very generically, Linux is an operating system kernel,
and UNIX is a certification for operating systems. The UNIX
standard evolved from the original Unix system developed at Bell
Labs. After Unix System V, it ceased to be developed as a single
operating system, and was instead developed by various competing
companies, such as Solaris (from Sun Microsystems), AIX (from IBM),
HP-UX (from Hewlett-Packard), and IRIX (from Silicon Graphics).
UNIX is a specification for baseline interoperability between these
systems, even though there are many major architectural differences
between them. Linux has never been certified as being a version of
UNIX, so it is described as being "Unix-like." A comprehensive list
of differences between Linux and "UNIX" isn't possible, because
there are several completely different "UNIX" systems.