What is difference between Linux kernel versions?

Question

What is Linux kernel versions(like 2.x, 3.x, 4.x)'s major difference?

And 2.x and 3.x version have stable version?

Answer 1

Actually I think you should know that stable/EOL and longterm mean:

As kernels move from the mainline into the stable category, two things can happen:

• They can reach End of Life after a few bugfix revisions, which means that kernel maintainers will release no more bugfixes for this kernel version, or
• They can be put into longterm maintenance, which means that maintainers will provide bugfixes for this kernel revision for a much longer period of time.

And here are longterm release kernels and stable kernels:

mainline:   4.10-rc4
stable:     4.9.4
stable:     4.8.17
longterm:   4.4.43
longterm:   4.1.37
longterm:   3.18.46
longterm:   3.16.39
longterm:   3.12.69
longterm:   3.10.104
longterm:   3.4.113
longterm:   3.2.84

If you want to see Linux kernel changelog or bugs,you can check out this,and also you can read the feature history of Linux kernel.

Hope this helps.

Answer 2

I have no experience whatsoever with kernel development but this same question about the significance of major version numbers came to my mind at some point too.

The first point of call to answer this question is The Linux Kernel Archives that groups the versions into:

• v0.x - historic
• v1.0 - changelog
• v1.1
• v1.2
• v1.3
• v2.0 - changelog
• v2.1 - development
• v2.2 - stable
• v2.3 - development
• v2.4 - stable, stayed around for ~10 years
• v2.5 - development
• v2.6 - stable, stayed around for ~12 years
• v3.x - the transition from version 2.6.39 to 3.0 is a perfectly normal version increment, following the pattern set for the 2.6 series *
• v4.x - switch from 3.x to 4.0 version numbers is entirely meaningless and it should not be associated to any important changes in the kernel *

So while up to version 2.6 there is a development/stable pattern (see timeline), from version 2.6 the different major version number appears to signify nothing and the things one should pay attention to when switching kernels is the changelog and length of support. Beyond that changing from 2 to 3 or from 3 to 4 is not going to be any different than switching from 3.x to 3.y.

There is a post on Unix & Linux that goes more into gore details of the highlights of particular kernel versions.