Main Linux kernel vs Ubuntu kernel

[Seth Forshee]

On Sat, Jun 09, 2018 at 12:07:12AM +0530, Subhashini Rao Beerisetty wrote:
> [ Please keep me in CC as I'm not subscribed to the list]
> 
> 
> Hi All,
> 
> 
> Apologies for the dull questions, I’m noob, need to learn lot more stuff.
> 
> 
> Ubuntu distro has LTS, non-LTS, GA, HWE kernels, what’s the difference
> between these?

GA: The kernel that originally ships with a given Ubuntu release.

LTS kernel: The GA kernel for an LTS release (not to be confused with
upstream LTS stable kernels - an Ubuntu LTS kernel may or may not also
be an upstream LTS kernel).

HWE kernel: A kernel backported from a non-LTS release to an LTS
release.

> Which one should be the best choice for development& validating the
> hardware?
> 
> 
> We’ve a bunch of hardware & test systems, we started this project by opting
> ubuntu distro 16.04 LTS v4.4 kernel for development of device drivers, test
> utilities.

It's difficult to answer your question without more information about
what you're hoping to accomplish. If you want to get new hardware
support into Ubuntu, usually that would land in the upstream kernel
first.

> I’d like to know, what are the differences between the main Linux kernel
> and the kernel being used by Ubuntu?

A given version of Ubuntu takes a specific upstream kernel version and
adds various extras, which may include extra drivers and backported
features from later kernel versions.

> If I need to upgrade our drivers to latest kernel v4.17, what are the best
> possible ways? In future, is it possible for us to use the current
> installed 16.04 LTS by just upgrading the Linux kernel version?

The easiest way to install the latest kernel version onto Ubuntu is to
use our mainline builds [1]. Understand though that these builds are
only for testing and will not receive support as far as fixing bugs,
etc.

> Are all the Linux kernel releases are backward compatible?

In broad strokes yes, as there is a pretty strict policy upstream about
not introducing regressions to userspace. However sometimes issues do
slip in, and you might also see problems if you try to install kernel
packages from a newer Ubuntu release into an older release. The only
supported way to run newer kernels is through the hwe packages, and
those are only provided for LTS releases.

Seth