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In 1984, Richard M. Stallman started the GNU project (https://gnu.org), recursively named by the phrase GNU is Not UNIX. As a project of the Free Software Foundation (FSF), GNU was intended to become a recoding of the entire UNIX operating system that could be freely distributed.

The GNU Project page (https://gnu.org/gnu/thegnuproject.html) tells the story of how the project came about in Stallman's own words. It also lays out the problems that proprietary software companies were imposing on those software developers who wanted to share, create, and innovate.

Although rewriting millions of lines of code might seem daunting for one or two people, spreading the effort across dozens or even hundreds of programmers made the project possible. Remember that UNIX was designed to be built in separate pieces that could be piped together. Because they were reproducing commands and utilities with well-known, published interfaces, that effort could easily be split among many developers.

It turned out that not only could the same results be gained by all new code, but in some cases that code was better than the original UNIX versions. Because everyone could see the code being produced for the project, poorly written code could be corrected quickly or replaced over time.

If you are familiar with UNIX, try searching the hundreds of GNU software packages, which contain thousands of commands, for your favorite UNIX command from the Free Software Directory (https://directory.fsf.org/wiki/GNU). Chances are good that you will find it there, along with many, many other available software projects.

Over time, the term free software has been mostly replaced by the term open source software. The term free software is preferred by the Free Software Foundation, while open source software is promoted by the Open Source Initiative (https://opensource.org).

To accommodate both camps, some people use the term Free and Open Source Software (FOSS) instead. An underlying principle of FOSS, however, is that although you are free to use the software as you like, you have some responsibility to make the improvements that you make to the code available to others. This way, everyone in the community can benefit from your work, as you have benefited from the work of others.

To define clearly how open source software should be handled, the GNU software project created the GNU Public License, or GPL. Although many other software licenses cover slightly different approaches to protecting free software, the GPL is the most well known—and it's the one that covers the Linux kernel itself. The GNU Public License includes the following basic features:

 Author rights: The original author retains the rights to their software.

 Free distribution: People can use the GNU software in their own software, changing and redistributing it as they please. They do, however, have to include the source code with their distribution (or make it easily available).

 Copyright maintained: Even if you were to repackage and resell the software, the original GNU agreement must be maintained with the software, which means that all future recipients of the software have the opportunity to change the source code, just as you did.

There is no warranty on GNU software. If something goes wrong, the original developer of the software has no obligation to fix the problem. However, many organizations, large and small, offer paid support (often in subscription form) for the software when it is included in their Linux or other open source software distribution. (See the section “OSI open source definition” later in this chapter for a more detailed definition of open source software.)

Despite its success in producing thousands of UNIX utilities, the GNU project itself failed to produce one critical piece of code: the kernel. Its attempts to build an open source kernel with the GNU Hurd project (https://gnu.org/software/hurd/) were unsuccessful at first, so it failed to become the premier open source kernel.