[CentOS-docs] Notes on HowTos/Custom Kernel

Thu Oct 2 18:43:30 UTC 2008
Akemi Yagi <amyagi at gmail.com>

On Thu, Oct 2, 2008 at 11:07 AM, Filipe Brandenburger
<filbranden at gmail.com> wrote:
> Hi Akemi,

> Actually, as you can probably see in my recent post to the CentOS
> list, I had to create a custom kernel to support a specific hardware
> that I had. I also needed XFS, that's why I did it over the CentOS
> Plus kernel.

As you later mentioned in your post, xfs is now provided as a kernel
module, kmod-xfs.  So, you do not really have to go for the cplus
kernel if this was the only reason (just a comment).

> It was not that hard to do it based on the original instructions, but
> there are some differences. For example, the snippet that starts at
> line 4779, the one that starts with "#if a rhel kernel, apply the rhel
> config options", that one is not present at all on the CentOS kernel,
> but I just went ahead and it worked fine.

That very change (deleting the "#if a rhel kernel,.." portion)
actually originated from the cplus kernel.  Mr. Hughes, with his great
talent, discovered that the presence of that section (template) was
preventing him from customizing the distro kernel when RHEL 5 was
released.  So, he added that note to the Custom Kernel wiki page as a
special note for CentOS-5 only.

> Another thing that bit me yesterday is that I used a "buildid" for my
> kernel, and then I could no longer load the XFS filesystem. I had to
> rebuild the xfs-kmod RPM as well, in that case I had to use a special
> rpmbuild command line so that it compiled it only for my arch, only
> for the default kernel (not xen, etc.) and for that specific buildid.
> I don't recall exactly which command line I used, and my build host
> was reinstalled soon after that, but if you wish I could try to
> reproduce that environment again in another machine to get it right
> and post it here.

As posted by Mr. Singh somewhere else, we will soon have kmods that
utilize the weak updates feature.  This means no more compilation of
the kmods for each kernel update.  I just heard that the new kmods for
the latest CentOS-5 kernel should be out any minutes now.

> Thanks a lot! The documentation looked great already, it looks even
> better now!!! :-D
> Filipe

Thank *you* for all the input and thoughts.