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Ubuntu 14.04 LTS has been released with Linux kernel 3.13 (development version) and not a stable version of the Linux kernel (3.14 or 3.12). Is thís because of many new features being added in Linux kernel 3.13?

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You are making the assumption that odd-numbered kernel releases are unstable, which has not been true since version 2.6.x. — that’s 2003. See the History part on http://en.wikipedia.org/wiki/Linux_kernel.

The development (unstable?) versions are now distributed in the various developers’ git trees; the thing more resembling the old odd-numbered kernels would be probably the linux-next git tree.

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You've been told that 3.13 is "just as stable" as 3.12 and 3.14. This is kinda-sorta true, in that the Linux kernel maintainers' policy these days is that every minor release deserves the "stable" label. Oh, and they idiosyncratically refer to the minor version number as the "major revision number". (Grade inflation, anyone?)

The thing that used to be called "stable" is now known as "long-term maintenance" (LTM), similar to the Ubuntu project's "long-term service" (LTS) designation.

The Linux kernel versions designated LTM are:

2.6.32  (Dec 2009)
3.2     (Jan 2012)
3.4     (May 2012)
3.10    (Jun 2013)
3.12    (Nov 2013)
3.14    (Mar 2014)
3.18    (Dec 2014)

Contrariwise, here are the kernel versions shipped inside recent Ubuntu LTS releases:

10.04.x  ->  2.6.32 LTM

12.04.0  ->  3.2 LTM
12.04.1  ->  3.2 LTM
12.04.2  ->  3.5
12.04.3  ->  3.8
12.04.4  ->  3.11
12.04.5  ->  3.13

14.04.0  ->  3.13
14.04.1  ->  3.13
14.04.2  ->  3.16

(Sources for 10.04: AskUbuntu, 10.04.4 release notes.)

As you can see, Ubuntu has not shipped a LTM version of the kernel inside their LTS release since 12.02.1 (released August 2012), and in fact they've even taken to shipping those historically "less stable" odd-numbered minor releases.

Because Ubuntu ships like clockwork every six months, and the Linux kernel's release schedule isn't tied to the calendar, the Ubuntu project has to choose whether to ship with the most recent LTM kernel (which might be several months old at that point) or to ship with the most recent "stable" kernel, period.

I don't know the backstory here, but my not-very-educated guess is that from the Ubuntu project's point of view, cutting-edge hardware driver support is more valuable than LTM designation. Ubuntu focuses on the desktop market, not the server market, so "does it support all my peripherals out of the box" is a more important question than "are we 100% sure it's bug-free."

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  • This is not the case. Canonical makes selected mainstream kernels LTS. These are ckt releases. They are maintained separately. And bugfixes and new hardware support are backported.
    – Pilot6
    May 26 '15 at 18:55
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    @Pilot6 that's part of the point. If Canonical had picked LTM kernels, then the kernel devs would do a significant amount of patching that now the Canonical team has to.
    – muru
    May 26 '15 at 19:10
  • according to ubuntu docs - that's not true. wiki.ubuntu.com/Kernel/LTSEnablementStack Canonical didn't pick longterm kernels, that's just a coincidence, they plan to use non-longterm releases in the future.
    – GioMac
    Feb 6 '17 at 18:44
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3.13 was the stable version of the kernel when it was decided to be used for Ubuntu 14.04. When 14.10 is released, the newer kernel will then also be backported to the LTS release, for enablement. This has been standard practice for years.

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  • My answer was not about what the upstream kernel team calls "stable."
    – dobey
    Feb 6 '17 at 19:07
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In the past even minor version numbers were reserved for stable kernels. This practice has been abandoned since a long time. Unstable kernel versions are now tagged with -rc<N>, where <N> is an increasing number.

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