Where did the name GNU/Linux come from? You've certainly heard of Linux before, and you may have heard of the GNU Project. You may not have heard the name GNU/Linux, although you're probably familiar with the system it refers to.
Linux is named after Linus Torvalds, the creator and original author of the kernel that runs a GNU/Linux system. The kernel is the program that performs the most basic functions of an operating system: It controls and interfaces with the computer's hardware, handles allocation of memory and other resources, allows multiple programs to run at the same time, manages the file system, and so on.
The kernel by itself doesn't provide features that are useful to users. It can't even provide a simple prompt for users to enter basic commands. It provides no way for users to manage or edit files, communicate with other computers, or write other programs. These tasks require the use of a wide array of other programs, including command shells, file utilities, editors, and compilers. Many of these programs, in turn, use libraries of general-purpose functions, such as the library containing standard C library functions, which are not included in the kernel.
On GNU/Linux systems, many of these other programs and libraries are software developed as part of the GNU Project. A great deal of this software predates the Linux kernel. The aim of the GNU Project is "to develop a complete UNIX-like operating system which is free software" (from the GNU Project Web site, http://www.gnu.org).
 GNU is a recursive acronym: It stands for "GNU's Not UNIX."
The Linux kernel and software from the GNU Project has proven to be a powerful combination. Although the combination is often called "Linux" for short, the complete system couldn't work without GNU software, any more than it could operate without the kernel. For this reason, throughout this book we'll refer to the complete system as GNU/Linux, except when we are specifically talking about the Linux kernel.