History

In April 1991, Linus Torvalds, at the time a 21-year-old computer science student at the University of Helsinki, Finland, started working on some simple ideas for an operating system. He started with a task switcher in Intel 80386 assembly language and a terminal driver. On 25 August 1991, Torvalds posted the following to comp.os.minix, a newsgroup on Usenet:

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 ... Yes - it's free of any minix code, and it has a multi-threaded fs. It is NOT protable sic (uses 386 task switching etc), and it probably never will support anything other than AT-harddisks, as that's all I have :-(.

On 17 September 1991, Torvalds prepared version 0.01 of Linux and put on the "ftp.funet.fi" – FTP server of the Finnish University and Research Network (FUNET). It was not even executable since its code still needed Minix for compilation and play.

On 5 October 1991, Torvalds announced the first "official" version of Linux, version 0.02. At this point, Linux was able to run Bash, GCC, and some other GNU utilities:

As I mentioned a month ago, I'm working on a free version of a Minix-lookalike for AT-386 computers. It has finally reached the stage where it's even usable (though may not be depending on what you want), and I am willing to put out the sources for wider distribution. It is just version 0.02...but I've successfully run bash, gcc, gnu-make, gnu-sed, compress, etc. under it.

After that, many people contributed code to the project, including some developers from the MINIX community. At the time, the GNU Project had created many of the components required for a free operating system, but its own kernel, GNU Hurd, was incomplete and unavailable. The Berkeley Software Distribution had not yet freed itself from legal encumbrances. Despite the limited functionality of the early versions, Linux rapidly gained developers and users.

Torvalds assigned version 0 to the kernel to indicate that it was mainly for testing and not intended for productive use. Version 0.11, released in December 1991, was the first self-hosted Linux, for it could be compiled by a computer running the same kernel.

When Torvalds released version 0.12 in February 1992, he adopted the GNU General Public License version 2 (GPLv2) over his previous self-drafted license, which had not permitted commercial redistribution. In contrast to Unix, all source files of Linux are freely available, including device drivers. The initial success of Linux was driven by programmers and testers across the world. With the support of the POSIX APIs, through the libC that, whether needed, acts as an entry point to the kernel address space, Linux could run software and applications that had been developed for Unix.

On 19 January 1992, the first post to the new newsgroup alt.os.linux was submitted. On 31 March 1992, the newsgroup was renamed comp.os.linux. The fact that Linux is a monolithic kernel rather than a microkernel was the topic of a debate between Andrew S. Tanenbaum, the creator of MINIX, and Torvalds. The Tanenbaum–Torvalds debate started in 1992 on the Usenet group comp.os.minix as a general discussion about kernel architectures.

Linux version 0.95 was the first to be capable of running the X Window System. In March 1994, Linux 1.0.0 was released with 176,250 lines of code. It was the first version suitable for use in production environments.

It started a versioning system for the kernel with three or four numbers separated by dots where the first represented the major release, the second was the minor release, and the third was the revision. At that time odd-numbered minor releases were for development and tests, whilst even numbered minor releases were for production. The optional fourth digit indicated a set of patches to a revision. Development releases were indicated with -rc ("release candidate") suffix.

The current version numbering is slightly different from the above. The even vs. odd numbering has been dropped and a specific major version is now indicated by the first two numbers, taken as a whole. While the time-frame is open for the development of the next major, the -rcN suffix is used to identify the n'th release candidate for the next version. For example, the release of the version 4.16 was preceded by seven 4.16-rcN (from -rc1 to -rc7). Once a stable release is made, its maintenance is passed off to the “stable team". Occasional updates to stable releases are identified by a three numbering scheme (e.g., 4.13.1, 4.13.2, ..., 4.13.16).

Version 1.2 (released 7 March 1995) gained support for computer systems using processors based on the Alpha, SPARC, and MIPS architectures.citation needed

After version 1.3 of the kernel, Torvalds decided that Linux had evolved enough to warrant a new major number, so he released version 2.0.0 in June 1996. The series included 41 releases. The major feature of 2.0 was support for symmetric multiprocessing (SMP) and support for more types of processors.

Starting with version 2.0, Linux is configurable for selecting specific hardware targets and for enabling architecture specific features and optimizations. The make *config family of commands of kbuild are used to enable and configure thousands of options for building ad hoc kernel executables (vmlinux) and loadable modules.

Version 2.2, released on 20 January 1999, removed the "Big Kernel Lock", that was a global spinlock, and provided improved SMP support, added support for the m68k and PowerPC architectures, and added new file systems (including read-only support for Microsoft's NTFS). In 1999, IBM published its patches to the Linux 2.2.13 code for the support of the S/390 architecture.

Version 2.4.0, released on 4 January 2001, contained support for ISA Plug and Play, USB, and PC Cards. It also included support for the PA-RISC processor from Hewlett-Packard. Development for 2.4.x changed a bit in that more features were made available throughout the duration of the series, including support for Bluetooth, Logical Volume Manager (LVM) version 1, RAID support, InterMezzo and ext3 file systems.

Version 2.6.0 was released on 17 December 2003. The development for 2.6.x changed further towards including new features throughout the duration of the series. Among the changes that have been made in the 2.6 series are: integration of µClinux into the mainline kernel sources, PAE support, support for several new lines of CPUs, integration of Advanced Linux Sound Architecture (ALSA) into the mainline kernel sources, support for up to 232 users (up from 216), support for up to 229 process IDs (64-bit only, 32-bit arches still limited to 215), substantially increased the number of device types and the number of devices of each type, improved 64-bit support, support for file systems which support file sizes of up to 16 terabytes, in-kernel preemption, support for the Native POSIX Thread Library (NPTL), User-mode Linux integration into the mainline kernel sources, SELinux integration into the mainline kernel sources, InfiniBand support, and considerably more.

Also notable are the addition of a wide selection of file systems starting with the 2.6.x releases: now the kernel supports a large number of file systems, some that have been designed for Linux, like ext3, ext4, FUSE, Btrfs, and others that are native of other operating systems like JFS, XFS, Minix, Xenix, Irix, Solaris, System V, Windows and MS-DOS.

In 2005 the stable team was formed as a response to the lack of a kernel tree where people could work on bug fixes, and it would keep updating stable versions. In February 2008 the linux-next tree was created to serve as a place where patches aimed to be merged during the next development cycle gathered. Several subsystem maintainers also adopted the suffix -next for trees containing code which they mean to submit for inclusion in the next release cycle. As of January 2014update, the in-development version of Linux is held in an unstable branch named linux-next.

Linux used to be maintained without the help of an automated source code management system until, in 2002, development switched to BitKeeper. It was freely available for Linux developers but it was not free software. In 2005, because of efforts to reverse-engineer it, the company which owned the software revoked the support of the Linux community. In response, Torvalds and others wrote Git. The new system was written within weeks, and in two months the first official kernel made using it was released.

Details on the history of the 2.6 kernel series can be found in the ChangeLog files on the 2.6 kernel series source code release area of kernel.org.

The 20th anniversary of Linux was celebrated by Torvalds in July 2011 with the release of the 3.0.0 kernel version. As 2.6 has been the version number for 8 years, a new uname26 personality that reports 3.x as 2.6.40+x had to be added to the kernel so that old programs would work.

Version 3.0 was released on 22 July 2011. On 30 May 2011, Torvalds announced that the big change was "NOTHING. Absolutely nothing." and asked, "...let's make sure we really make the next release not just an all new shiny number, but a good kernel too." After the expected 6–7 weeks of the development process, it would be released near the 20th anniversary of Linux.

On 11 December 2012, Torvalds decided to reduce kernel complexity by removing support for i386 processors, making the 3.7 kernel series the last one still supporting the original processor. The same series unified support for the ARM processor.

Version 3.11, released on 2 September 2013, adds many new features such as new O_TMPFILE flag for open(2) to reduce temporary file vulnerabilities, experimental AMD Radeon dynamic power management, low-latency network polling, and zswap (compressed swap cache).

The numbering change from 2.6.39 to 3.0, and from 3.19 to 4.0, involved no meaningful technical differentiation. The major version number was increased to avoid large minor numbers. Stable 3.x.y kernels were released until 3.19 in February 2015.

In April 2015, Torvalds released kernel version 4.0. By February 2015, Linux had received contributions from nearly 12,000 programmers from more than 1,200 companies, including some of the world's largest software and hardware vendors. Version 4.1 of Linux, released in June 2015, contains over 19.5 million lines of code contributed by almost 14,000 programmers.

A total of 1,991 developers, of whom 334 are first collaborators, added more than 553,000 lines of code to version 5.8, breaking the record previously held by version 4.9.

According to the Stack Overflow’s annual Developer Survey of 2019, more than the 53% of all respondents have developed software for Linux OS and about 27% for Android, although only about 25% develop with Linux-based operating systems.

Most websites run on Linux-based operating systems and all of the world's 500 most powerful supercomputers use some kind of OS based on Linux.

Linux distributions bundle the kernel with system software (eg., the GNU C Library, systemd, and others Unix utilities and daemons) and a wide selection of application software, but their usage share in desktops is low in comparison to other operating systems.

Android, which accounts for the majority of the installed base of all operating systems for mobile devices, is responsible for the rising usage of the Linux kernel, together with its wide use in a large variety of embedded devices.