History of Unix and Linux

An outline of the history of Unix and Linux.

Location: Bell Labs, part of AT&T (New Jersey), late 1960s through early 1970s

  • Starts with an operating system called Multics.
  • Multics was a time sharing system
    • That is, more than one person could use it at once.
  • But Multics had issues and was slowly abandoned
  • Ken Thompson found an old PDP-7. Started to write UNIX.
    • The ed line editor was written.
    • Pronounced e.d. but generally sounded out.
  • This version of UNIX would later be referred to as Research Unix
  • Dennis Ritchie, the creator of the C programming language, joined Thompson's efforts.

Location: Berkeley, CA (University of California, Berkeley), early to mid 1970s

  • The code for UNIX was not 'free software' but low cost and easily shared.
  • Ken Thompson visited Berkeley and helped install Version 6 of UNIX
  • Bill Joy and others contributed heavily
    • Joy created the vi text editor, a descendant of the popular Vim editor, many other important programs, and was a co-founder of Sun Microsystems
  • This installation of UNIX would eventually become known as the Berkeley Software Distribution, or BSD.


  • Until its breakup in 1984, AT&T was not allowed to profit off patents that were not directly related to its telecommunications businesses.
  • This agreement with the US government helped protect the company from monopolistic charges, and as a result, they could not commercialize UNIX.
  • This changed after the breakup. System V UNIX became the standard bearer of commercial UNIX.

Location: Boston, MA (MIT), early 1980s through early 1990s

  • In the late 1970s, Richard Stallman noticed that software began to become commercialized.
    • As a result, hardware vendors stopped sharing the code they developed to make their hardware work.
  • Software code became eligible for copyright protection with the Copyright Act of 1976
  • Stallman, who thrived in a hacker culture, began to battle against this turn of events.
  • Stallman created the GNU project, the free software philosophy, GNU Emacs, a popular and important text editor, and he wrote many other programs.
  • The GNU project is an attempt to create a completely free software operating system, that was Unix-like, called GNU.
  • By the early 1990s, Stallman and others had developed all the utilities needed to have a full operating system, except for a kernel, which they called GNU Hurd.
  • This included the Bash shell, written by Brian Fox.
  • The GNU philosophy includes several propositions that define free software:

The four freedoms, per GNU Project: 0. The freedom to run the program as you wish, for any purpose (freedom 0).

  1. The freedom to study how the program works, and change it so it does your computing as you wish (freedom 1). Access to the source code is a precondition for this.
  2. The freedom to redistribute copies so you can help others (freedom 2).
  3. The freedom to distribute copies of your modified versions to others (freedom 3). By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.

The Four Freedoms

The Unix wars and the lawsuit, late 1980s through the early 1990s

  • AT&T, after its breakup, began to commercialize Unix, and differences in AT&T Unix and BSD Unix arose.
  • The former was aimed at commercialization, and the latter aimed at researchers and academics.
  • UNIX Systems Laboratories, Inc. (USL, part of AT&T) sued Berkeley Software Design, Inc. (BSDi, part of the University of California, Berkeley) for copyright and trademark violations.
  • USL ultimately lost the case, but the lawsuit delayed adoption of BSD Unix.

Linux, Linus Torvalds, University of Helsinki, Finland, early 1990s

  • On August 25, 1991, Linus Torvalds announced that he had started working on a free operating system kernel for the 386 CPU architecture and for his specific hardware.
  • This kernel would later be named Linux.
  • Linux technically refers only to the kernel.
    • An operating system kernel handles startup, devices, memory, resources, etc.
    • A kernel does not provide user land utilities---the kinds of software they people use when using computers.
  • Torvalds' motivation was to learn about OS development but also to have access to a Unix-like system.
    • He already had access to an Unix-like system called MINIX, but MINIX had technical and copyright restrictions.
  • Torvalds has stated that if a BSD or if GNU Hurd operating system were available, then he may not have created the Linux kernel.
  • But Torvalds and others took the GNU utilities and created what is now called Linux or GNU/Linux.

Distributions, early 1990s through today

  • Soon after the Linux development, people would create their own Linux and GNU based operating systems and would distribute them.
  • As such, these Linux operating systems became referred to as distributions.
  • The two oldest distributions that are still in active development include:

Short History of BSD, 1970s through today

  • Unix version numbers 1-6 eventually led to BSD 1-4.
  • At BSD 4.3, all versions had some AT&T code.
    • Desire to remove this code led to BSD Net/1.
  • All AT&T code was removed by BSD Net/2.
  • BSD Net/2 was ported to the Intel 386 processor.
    • This became 386BSD and was made available in 1992, a year after the Linux kernel was released.
  • 386BSD split into two projects:
  • NetBSD split into another project: OpenBSD.
  • All three of these BSDs are still in active development.
  • From a bird's eye point of view, they each have different focuses:
    • NetBSD focuses on portability (MacOS, NASA)
    • FreeBSD focuses on wide applicability (WhatsApp, Netflix, PlayStation 4, MacOS)
    • OpenBSD focuses on security (has contributed a number of very important applications)

MacOS is based on Darwin, is technically UNIX, and is partly based on FreeBSD with some code coming from the other BSDs. See Why is macOS often referred to as 'Darwin'? for a short history.

Short History of GNU, 1980s through today

  • The GNU Hurd is still under active development, but it's the pre-production state.
  • The last release was 0.9 on December 2016.
  • A complete OS based on the GNU Hurd can be downloaded and ran. For example: Debian GNU/Hurd

Free and Open Source Licenses

In the free software and open source landscape, there are several important free and/or open source licenses that are used. The two biggest software licenses are based on the software used by GNU/Linux and the software based on the BSDs. They each take very different approaches to free and/or open source software. The biggest difference is this:

  • Software based on software licensed under the GPL must also be licensed under the GPL. This is referred to as copyleft software, and the idea is to propagate free software.
  • Software based on software licensed under the BSD license may be closed source and primarily must only attribute the original source code and author.