Textbook of Linux

Unix is the family of operating systems that began at AT&T's Bell Labs in 1969, when Ken Thompson, Dennis Ritchie, and colleagues built a small, portable, multi-user OS on a disused PDP-7. Originally a pun on the earlier Multics project, Unix embodied a distinctive philosophy: build small tools that do one thing well, and let users combine them through pipes and shell scripts. Its rewrite in C in 1973 made it portable across hardware architectures, a then-radical idea.

Through the 1970s and 80s, Unix spread from Bell Labs to universities (where Berkeley produced the influential BSD variants) and commercial vendors (SunOS, HP-UX, AIX, IRIX, Ultrix, and many more). Legal and technical fragmentation—collectively remembered as the "Unix wars"—ultimately left room for Linux and the free BSDs to emerge as the dominant Unix-like systems of the post-2000 era. Today, certified "Unix" refers to systems conforming to The Open Group's Single UNIX Specification, but the Unix tradition encompasses all of Linux, macOS, BSD, Solaris, and many embedded systems.

Unix's influence on computing is incalculable. The shell, pipes, filesystem hierarchy, tree of processes, C programming language, text-file configuration, and do-one-thing-well philosophy all originated in or were crystallised by Unix. A Linux user in 2026 working at the shell is, in many important senses, using a system that would be recognisable—if somewhat bewildering in its abundance—to Ken Thompson in 1975.