Kernel Release Numbering Redux
(Tue, 15 Jul 2008 19:14:45 +0000)
For many years, each Linux kernel release was assigned a series of three numbers, X.Y.Z, with an even Y indicating a "stable" release, and an odd Y indicating an "unstable" development release. Z was incremented for each individual kernel release. The "stable" 1.0.0 Linux kernel was released in March of 1994. New development was then continued in the "unstable" 1.1.z branch, until the "stable" 1.2.0 Linux kernel was release in March of 1995. Major improvements in the kernel lead to X being incremented to 2, and a "stable" 2.0 kernel was released in June of 1996. Active development then continued in the "unstable" 2.1 tree. This process continued with "stable" 2.2, 2.4 and 2.6 kernel trees, and each stable tree gained an official maintainer while Linux creator Linus Torvalds focused on newer features in the next "unstable" tree. Development in these "unstable" trees could go on for periods of multiple years before a "stable" tree was branched.
This long-standing odd/even development model was officially scrapped in 2004 thanks to the success that Linus and Andrew Morton were having working together, and significant "unstable" development began happening between each 2.6.Z release. In a recent thread it was asked what it would take for an "unstable" 2.7 development tree to be created, to which Linus noted replied:
"Nothing. I'm not going back to the old model. The new model is so much better that it's not even worth entertaining as a theory to go back. That said, I _am_ considering changing just the numbering. Not to go back to the old model, but because a constantly increasing minor number leads to big numbers. I'm not all that thrilled with '26' as a number: it's hard to remember. [..] I think the time-based releases (ie the '2 weeks of merge window until -rc1, followed by roughly two months of stabilization') has been so successful that I'd prefer to skip the version numbering model too. We don't do releases based on 'features' any more, so why should we do version _numbering_ based on 'features'?"