Linux is an open-source operating system, based on the Linux kernel. The different Linux versions are called Linux Distributions. Most Linux distributions are free, some offer the operating system for free but charge for support. Linux was created by Linus Torvalds who wanted an operating system that was similar to Unix. Originally, Linux was used mostly as an operating system for servers. Lately, it has become more popular on desktop computers and with the rise of smartphones, Linux is everywhere. These lessons cover material where Linux was used in combination with other networking devices like routers, switches and/or firewalls.