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This article is about the Linux Kernel. For the system that the kernel runs under in most cases, see GNU/Linux
Linux is a Unix-like kernel. It was created in April 1991 in University of Helsinki, Finland by Linus Torvalds. It is one of the most prominent examples of free software. It is released under GNU General Public License version 2 (GPLv2), with some proprietary binary modules.
Being a kernel, Linux sets the foundations for the operating system but lacks the actual userspace programs commonly associated with one. Due to convenience and historical purposes, Linux ships with GNU core utilities in order to provide a fully functional system. Due to this fact, some refer to it as GNU/Linux, which is a term Richard Stallman repeatedly tries to enforce. However, non-GNU core utilities are available and do ship with a few distros.
While being a student in the University of Helsinki, Linus Torvalds created the kernel as a hobby. He advertised it on the Usenet group
comp.os.minix shortly after the first alpha was created.
Hello everybody out there using minix - I'm doing a (free) operating system (just a hobby, won't be big and professional like gnu) for 386(486) AT clones. This has been brewing since april, and is starting to get ready. I'd like any feedback on things people like/dislike in minix, as my OS resembles it somewhat (same physical layout of the file-system (due to practical reasons) among other things). I've currently ported bash(1.08) and gcc(1.40), and things seem to work. This implies that I'll get something practical within a few months, and I'd like to know what features most people would want. Any suggestions are welcome, but I won't promise I'll implement them :-) Linus ([email protected]) PS. Yes - it's free of any minix code, and it has a multi-threaded fs. It is NOT protable (uses 386 task switching etc), and it probably never will support anything other than AT-harddisks, as that's all I have :-(.
Soon after, the early adopters of the Linux kernel expanded greatly.
In 1992, with the growing popularity of the Linux kernel, creator of MINIX Andrew S. Tanenbaum started an argument with Linus Torvalds in the comp.os.minix newsgroup, claiming that how the Linux kernel was created, it was already obsolete. The debate was primarially about microkernels vs monolithic kernels. It is widely considered one of the earliest flame wars on the Internet.
In the late 1990's, RMS saw that systems that had the Linux kernel as the base were becoming more and more popular. However, these were, in fact, a GNU system because it utilizes the incomplete GNU OS that was planned to be completed with the Herd kernel. Because of this, he coined the new terms for the system: GNU/Linux (Pronounced GAHNOO slash Linux), or (and lesser used) GNU+Linux (GAHNOO plus Linux). It was advised to not simply say GNU Linux because it would imply that Linux was a creation of the GNU Project.
Throughout its history (as with most other UNIX-Like systems), the Linux Kernel was challenged for patent. Many people believed that the first beta version of Linux was made from MINIX code, meaning its patent would have been violated and Linus Torvalds would have to cease and desist. While the creator of the MINIX kernel says that he believes Linux has no MINIX code, others believe that it did (or does). In addition, multiple claims were made that the use of Linux (and many other UNIX systems) is a violation of patents owned by SCO Semiconductor Group. who inherited the original patents for the UNIX system.
Alternative Linux Kernels
In addition to certain, well known patchsets such as grsecurity or linux-ck, many distributions have their own kernel and patches that attempt to satisfy requirements for their most common use-cases.
grsecurity is an extensive security enhancement to the Linux kernel that defends against a wide range of security threats through intelligent access control, memory corruption-based exploit prevention, and other system hardening that generally requires no additional configuration. It has been actively developed and maintained for the past 13 years. Commercial support for grsecurity is available through Open Source Security, Inc.
Linux-ck is a package available in the AUR and in the linux-ck repo that allows users to run a kernel/headers setup patched with Con Kolivas' ck1 patchset, including the Brain Fuck Scheduler (BFS). Many Archers elect to use this package for the BFS' excellent desktop interactivity and responsiveness under any load situation. Additionally, the bfs imparts performance gains beyond interactivity.
Linux-libre is a alternative kernel that is maintained from modified versions of the Linux kernel. The aim of the project is to remove from the Linux kernel any software that does not include its source code, has its source code obfuscated, or is released under proprietary licenses. While usable for most purposes, it does not include a myriad of firmware nor any binary blobs.