Linux kernel 版本号？

Question

I'm somewhat confused on the Linux kernel version numbers. I noticed that many Linux distributions do no use the latest Kernels, in fact I have seen a few using version 2.4. Is there a reason for this? Is there any differences between 2.4, 2.6, 3.2 apart from age? What are the security implications of using an older kernel?

Answer 1

Different kernels have different features and improvements the developers of a distribution take a look at features they are going to support then decide which kernel to use based on the most stable support of that kernel.

It is the decision of the distribution developer which one to use, and they would go with the one they felt comfortable with.

This is a feature of software development its like asking what Java 1.1 and Java 1.7 is and whats the difference is apart from age... the answer is many things.

Most kernels and software will also have a security patch schedule and it is up to the user to keep their systems patched and up to date if you do not then you invite security issues as they are never fixed.

Answer 2

between major releases (eg 2.4 and 2.6), new features are introduced and old features are deprecated, eventually making the kernel binary incompatible.

this is important if you depend on some kernel-module that is not part of the mainline kernel (eg it is proprietary and the original authors don't provide updated modules; or it is open source (but never made it into the kernel) and nobody is willing to spend time to migrate the code)

also a new major release might change the system behaviour significantly. i remember that when switching from 2.4 to 2.6, many people that needed low latency audio (that's my background, so forgive me) would stay with the old kernel, since the new scheduling algorithms performed worse in some situations.

Answer 3

I hope the below page would help us in understanding the linux version numbering system: http://www.linfo.org/kernel_version_numbering.html

A snap from http://www.tldp.org/FAQ/Linux-FAQ/kernel.html#linux-versioning

Linux version numbers follow a longstanding tradition. Each version has three numbers, ie, XYZ The "X" is only incremented when a really significant change happens, one that makes software written for one version no longer operate correctly on the other. This happens very rarely -- in Linux's history it has happened exactly once.

The "Y" tells you which development "series" you are in. A stable kernel will always have an even number in this position, while a development kernel will always have an odd number.

The "Z" specifies which exact version of the kernel you have, and it is incremented on every release.

Answer 4

There is a human-readable changelog for the Linux Kernel .

Some people take the attitude "if it works - don't change it". So, there are security implications of running an older kernel - but there's also the risk that upgrading may break something.

Answer 5

As kernels improve/change, they might break expectations that held on earlier versions. If a distribution becomes unstable because too many software breaks under the new version of the kernel, the developers might opt to use an earlier version until the software is able to handle the changes in the new kernel.

Answer 6

Typically a binary image may not be portable between kernels where the first or second part of the version number changes. So in order to upgrade from 2.4 to 2.6, a large proportion of libs and executables will need to be upgraded / recompiled too. This can be a particular problem if you use closed source applications/drivers.

Most Linux distributors will back port patches from newer kernel versions depending on the security impact / demand for additional functionality. If you're not able to upgrade your entire system at regular intervals, then you need to find a distribution which explicitly supports a long support cycle with a good history of back porting (eg RHEL, SuSE).