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Linux (kernel)
This article is about the kernel, Linux. For the system that the kernel runs under in most cases, see GNU/Linux
Linux is a Unix-like kernel. Development begun in April 1991 in the University of Helsinki, Finland by Linus Torvalds. It is one of the most prominent examples of free software. It was released publicly on 17 September 1991, as proprietary software [1]. In 1992 it was re-licensed to the GNU General Public License version 2 (GPLv2), although many proprietary blobs were later added, beginning in 1995.
Being a kernel, Linux sets the foundations for the operating system but lacks the actual userspace programs required to operate[2]. For usability, convenience and historical purposes, Linux is often combined with an init, GNU software (usually including GNU coreutils) and many other free software programs 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 consistently recommends. However, non-GNU coreutils are available and do ship with a few distros.
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History
While being a student in the University of Helsinki, Linus Torvalds wrote the kernel as a hobby. He advertised it on the Usenet group comp.os.minix shortly after the first alpha was written.
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 Linux expanded greatly.
Controversy
In 1992, with the growing popularity of Linux, author of MINIX Andrew S. Tanenbaum started an argument with Linus Torvalds in the comp.os.minix newsgroup, claiming that when Linux was released, it was already obsolete [3]. The debate was primarily 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 used the kernel, Linux were becoming more and more popular. However, almost all of these were, in fact, a GNU system because they utilized the incomplete GNU OS that was planned to be completed with the Hurd kernel. Because of this, he coined the new terms for these systems: GNU/Linux (Pronounced GAHNOO slash Linux), or (and lesser used) GNU+Linux (GAHNOO plus Linux). He has advised to not simply say GNU Linux because that would imply that Linux is a GNU package.
Throughout its history (as with most other UNIX-like systems), Linux was threatened by software patents. Many people believed that the first beta version of Linux was made from MINIX code, meaning its copyright had been violated and Linus Torvalds would have to cease and desist. While the author of the MINIX kernel said 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 GNU/Linux (and many other Unix-like OS's) is a violation of patents held by SCO Semiconductor Group, who claimed to have inherited the original software patents for UNIX.
Alternative Kernels
Alternative kernels are variations to, or patch sets of Linux.
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
grsecurity is an extensive security enhancement to Linux 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
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.
GNU Linux-libre
GNU Linux-libre is a patchset on mainline Linux. The aim of the project is to remove from Linux any software that does not include its source code, has its source code obfuscated, is released under proprietary licenses, or relies on separate proprietary software to function. While usable for most purposes, it does not include a myriad of firmware nor any binary blobs.
