Linux: Linux kernel

Chen Weixiang @ Dec 16, 2015 | TAG: Linux

This article introduces the most important part of Linux system: kernel.

Linux kernel

The Linux kernel is the most important part of the Linux system. You can get Linux kernel source code from its official site The Linux Kernel Archives. Also you can browse Linux kernel source code on git repositories for the Linux kernel mainline, Linux kernel stable tree and linux-next integration testing tree.

Linux kernel Releases

Here is a short history of Linux kernel (until December 06, 2015):

kernel version Release date Status Note
0.01 Sep 17, 1991 EOL  
0.10 Nov 1991 EOL  
0.11 Dec 1991 EOL The first version to be self-hosted, as Linux kernel 0.11 could be compiled by a computer running the same kernel version.
0.12 Feb 1992 EOL Adopt the GNU General Public License (GPL).
0.95 Mar 08, 1992 EOL The first version to be capable of running X Window System.
1.0 Mar 14, 1994 EOL  
1.1 Apr 06, 1994 EOL  
1.2 Mar 07, 1995 EOL  
pre2.0 May 12, 1996 EOL  
1.3 Jun 12, 1995 EOL  
2.0 Jun 09, 1996 EOL  
2.2 Jan 26, 1999 EOL  
2.4 Jan 04, 2001 EOL  
2.6 Dec 17, 2003 EOL  
2.6.11 Mar 02, 2005 EOL  
2.6.12 Jun 18, 2005 EOL  
2.6.13 Aug 28, 2005 EOL  
2.6.14 Oct 27, 2005 EOL  
2.6.15 Jan 02, 2006 EOL  
2.6.16 Mar 20, 2006 EOL  
2.6.17 Jun 17, 2006 EOL  
2.6.18 Sep 20, 2006 EOL  
2.6.19 Nov 26, 2006 EOL  
2.6.20 Feb 04, 2007 EOL  
2.6.21 Apr 25, 2007 EOL  
2.6.22 Jul 08, 2007 EOL  
2.6.23 Oct 09, 2007 EOL  
2.6.24 Jan 24, 2008 EOL  
2.6.25 Apr 16, 2008 EOL  
2.6.26 Jul 13, 2008 EOL  
2.6.27 Oct 09, 2008 EOL  
2.6.28 Dec 12, 2008 EOL  
2.6.29 Mar 23, 2009 EOL  
2.6.30 Jun 09, 2009 EOL  
2.6.31 Sep 09, 2009 EOL  
2.6.32 Dec 02, 2009 Longterm  
2.6.33 Feb 24, 2010 EOL  
2.6.34 May 16, 2010 EOL  
2.6.35 Aug 01, 2010 EOL  
2.6.36 Oct 20, 2010 EOL  
2.6.37 Jan 04, 2011 EOL  
2.6.38 Mar 14, 2011 EOL  
2.6.39 May 18, 2011 EOL  
3.0 Jul 21, 2011 EOL Release kernel 3.0 to mark the kernel’s 20th anniversary.
3.1 Oct 24, 2011 EOL  
3.2 Jan 04, 2012 Longterm  
3.3 Mar 18, 2012 EOL  
3.4 May 20, 2012 Longterm  
3.5 Jul 21, 2012 EOL  
3.6 Sep 30, 2012 EOL  
3.7 Dec 10, 2012 EOL  
3.8 Feb 18, 2013 EOL  
3.9 Apr 28, 2013 EOL  
3.10 Jun 30, 2013 Longterm  
3.11 Sep 02, 2013 EOL  
3.12 Nov 03, 2013 Longterm  
3.13 Jan 19, 2014 EOL  
3.14 Mar 30, 2014 Longterm  
3.15 Jun 08, 2014 EOL  
3.16 Aug 03, 2014 EOL  
3.17 Oct 05, 2014 EOL  
3.18 Dec 07, 2014 Longterm  
3.19 Feb 08, 2015 EOL  
4.0 Apr 12, 2015 EOL  
4.1 Jun 22, 2015 Longterm  
4.2 Aug 30, 2015 Stable  
4.3 Nov 01, 2015 Stable  
4.4 Dec 06, 2015 Mainline  

If we draw a picture of Linux kernel releases, it should be like this:

Linux_Kernel_Releases

Linux_Kernel_Timeline

Version Numbering

The Linux kernel has had three different numbering schemes:

  • First numbering scheme: kernel 0.01 ~ 1.0

    The first scheme was used in the run-up to 1.0. The first version of the kernel was 0.01. This was followed by 0.02, 0.03, 0.10, 0.11, 0.12 (the first GPL version), 0.95, 0.96, 0.97, 0.98, 0.99 and then 1.0. From 0.95 on there were many patch releases between versions.

  • Second numbering scheme: kernel 1.0 ~ 2.6.0, Even-odd version numbering scheme

    After the 1.0 release and prior to version 2.6, the number was composed as x.y.z, where the number x denoted the kernel version, the number y denoted the major revision of the kernel, and the number z indicated the minor revision of the kernel. The kernel version was changed only when major changes in the code and the concept of the kernel occurred (Note: version 3.0 was released in 2011, but it was not a major change in kernel concept). The major revision was assigned according to the even-odd version numbering scheme. The minor revision had been changed whenever security patches, bug fixes, new features or drivers were implemented in the kernel.

  • Third numbering scheme: kernel 2.6.0 ~ present, Time-based release numbering scheme

    After version 2.6.0 was released in 2004, a time-based release cycle was adopted. For about seven years, the first two numbers remained 2.6, and the third number was incremented with each new release, which rolled out after two to three months. A fourth number was sometimes added to account for bug and security fixes (only) to the kernel version. The even-odd system of alternation between stable and unstable was gone. Instead, development pre-releases are titled release candidates, which is indicated by appending the suffix -rc to the kernel version, followed by an ordinal number.

    The first use of the fourth number occurred when a grave error, which required immediate fixing, was encountered in 2.6.8’s NFS code. However, there were not enough other changes to legitimize the release of a new minor revision (which would have been 2.6.9). So, 2.6.8.1 was released, with the only change being the fix of that error. With 2.6.11, this was adopted as the new official versioning policy. Later it became customary to continuously back-port major bug-fixes and security patches to released kernels and indicate that by updating the fourth number.

    On 29 May 2011, Linus Torvalds announced that the kernel version would be bumped to 3.0 for the release following 2.6.39, due to the minor version number getting too large and to commemorate the 20th anniversary of Linux. It continued the time-based release practice introduced with 2.6.0, but using the second number; for example, 3.1 would follow 3.0 after a few months.

    The major version number was also raised to 4 announced on 22 Feb 2015, for the release following version 3.19.

References