Linux is frequently called a free operating system, but that all depends on what you call free – and what you call an operating system. When Richard Stallman launched the Free Software movement in 1983, he had a very specific vision in mind that was codified in what became known as the Four Software Freedoms (see the "Four Freedoms" box) [1]. Although the Linux kernel is distributed under a free license and is thus classified as free software, many other components are commonly packaged with the Linux kernel, and some of them aren't so free. Furthermore, a Linux distribution (or GNU/Linux distribution in the parlance of the Free Software community) is more than just the kernel and often contains thousands of software packages, including applications, libraries, firmware, drivers, codecs, and other components – all with their own licenses and development goals.

The truth is, since 1996, the Linux kernel has included what are known as proprietary or binary blobs – software or firmware that is free to distribute but is not free-licensed and does not come with source code. These blobs often include drivers for WiFi, sound, or Ethernet. To make matters worse, many distributions come with proprietary tools that require proprietary software, such as VirtualBox.

Most mainstream distros accept binary blobs, because they believe including these components with the distribution makes the system more user-friendly and improves hardware compatibility. The Free Software Foundation (FSF), however, considers binary blobs a violation of the Four Software Freedoms, because these blobs are distributed without source code and therefore cannot be studied or improved. Moreover, since the blobs cannot be studied, no one can be sure what they contain, and they are a potential threat to privacy and security.

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