Linux Kernel Versioning: Debian Sid vs Ubuntu Precise

I have setup two machines:

On one machine I have installed Ubuntu Precise 12.04 beta and dist-upgraded to the latest packages.

On the other machine I have installed Debian Sid Unstable and dist-upgraded to the latest packages.

On the Ubuntu machine uname -a reads:

Linux 3.2.0-20-generic #32-Ubuntu SMP Thu Mar 22 02:22:46 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

On the Debian machine uname -a reads:

Linux 3.2.0-2-amd64 #1 SMP Wed Mar 28 13:28:04 UTC 2012 x86_64 GNU/Linux

My question is about the kernel versions:

Ubuntu: 3.2.0-20-generic
Debian: 3.2.0-2-amd64

Version 3.2 of Linux was released on:

linux-3.2.tar.gz         05-Jan-2012 00:40   94M

Since then there have been 13 point releases, 3.2.1 .. 3.2.13 from kernel.org, and 3.3 released.

My question is about the history of the source tree of the two kernels on my two machines:

From which release of official kernel.org kernel are those two versions of the kernel derived?

What is the relationship of the sources of the Debian Sid kernel to the Ubuntu Precise one?

Are the changes made from the kernel.org sources to produce 3.2.0-2-amd64 also present in 3.2.0-20-generic on Ubuntu?

Is the Debian Sid kernel "upstream" of the Ubuntu one?

What does the fourth version number mean (after the first dash) "2" in the case of Debian and "20" in the case of Ubuntu - and how does it relate to the above?

Answer

The Ubuntu kernel is not the same as the upstream kernel, although the version numbers may be similiar. You can read about the Ubuntu Kernel in the Ubuntu Wiki which answers your first and your fourth question:

Beta-2 includes the 3.2.0-20.33 Ubuntu kernel which is based on the v3.2.12 upstream stable Linux kernel.

The Ubuntu Kernel FAQ describes the version numbering as follows:

Given a version like 2.6.35-6.9-generic this can be broken into four
parts as below:

-.-
The base kernel version represents the mainline version on which the Ubuntu

kernel is based. The ABI number represents significant changes in the
kernel Application Binary Interface. The upload number is a
monotonically increasing counter for each upload of this base version.
The flavour indicates which kernel configuration variant this is

You can also check the Ubuntu to Mainline kernel version mapping for more information on ubuntu kernel versions vs upstream kernel versions.