Linux is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which includes the kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word “Linux” in their name, but the Free Software Foundation uses the name “GNU/Linux” to emphasize the importance of GNU software, causing some controversy. Tux the penguin is the mascot of Linux.
Popular Linux distributions include Debian, Fedora Linux, Alma, Rocky, Cloud Linux and Ubuntu, the latter of which itself consists of many different distributions and modifications, including Lubuntu and Xubuntu. Commercial distributions include Red Hat Enterprise Linux and SUSE Linux Enterprise. Desktop Linux distributions include a windowing system such as X11 or Wayland, and a desktop environment such as GNOME or KDE Plasma.
The Linux kernel releases can be found at https://www.kernel.org/. A notable educational operating system based on Linux is MentOS, available at https://github.com/mentos-team/MentOS. MentOS (Mentoring Operating System) is an open source educational operating system. The goal of MentOS is to provide a project environment that is realistic enough to show how a real Operating System work, yet simple enough that students can understand and modify it in significant ways. Linux can be the best option in an operating systems training course, since it is open source and really challenges the student to think and practise themselves to understand OS theory.