[CentOS-virt] CentOS 6 VM image for paravirtualizaton on CentOS Xen server

Mon Mar 16 02:45:03 UTC 2015
Nico Kadel-Garcia <nkadel at gmail.com>

On Sun, Mar 15, 2015 at 8:11 PM, Peter <peter at pajamian.dhs.org> wrote:
> On 03/16/2015 11:25 AM, Nico Kadel-Garcia wrote:
>> I've got CentOS VM's running fine, and have done them before. But
>> previously, I deployed the same base OS on the VM as on the Xen
>> server, so paravirtualization posed few risks. And I had control of
>> the DHCP setup. so I could trivially set up a tftp server to do a
>> non-CD installation, because Xen, at last look, doesn't support
>> installing a paravirtualized host from a CD image.
> It does as long as (1) the kernel has Xen PV support (CentOS 6 standard
> kernel does) and (2) it has the necessary drivers in the initrd (I think
> this is where the CD image is lacking), then you should, in theory, be
> able to pv-grub boot to the CD.  Alternatively you can boot to the CD on

Not according to the Xen guidelines I was finding. If they're
incorrect, *for a CentOS 5 Xen hypervisor*, I'd love to be able to use
that. Unfortunately, one of the banes of my technology existence is
when people say "that works great!" and "just look on Google,!", and
the answer they vaguely remember does not actually include the
situation I desdcribed.

> another box first, copy the kernel off to a USB stick, and generate a
> new initrd with the xen drivers included, then put those on the Xen host
> and boot to the VM CD image using those in the kernel= and initrd= lines
> in the domain.cfg file.

Ouch. I've hand-modified CD and DVD images in the past, it's a pain
the neck, It's been compunded by the insistece that the  compressed
"vmlinuz" file is, itself, named "vmlinuz" instead of "vmlinuz.gz",
which always struck me as fairly nutty.

> The other way is to boot to the CD as an HVM domain and install, then
> convert it to a PV domain afterwards, which is not all that difficult to do.

This would probably be safest for me right now, since I have a
testable HVM instance of CentOS 6 to copy and work with. I'm not
finding any good guidelines for migrating from HVM to
paravirtualizaton for old Xen environments. Have you seen any, or done
this process? The notes I find often include extraneous and hopefully
unnecessary steps, such as http://support.citrix.com/article/CTX121875
saying. It's legible, but leaves out the kind of incompatibility
issues that I;ve been concerned about hopping from a Xen server on
CentOS 5.x to a CentOS 6.x guest.

> There is a third way which involves using yum to install the @core group
> plus kernel to an image, then tweak and boot to that as a PV domain.
> This is how I have done it in the past.

I'm sorry, but what? Are you building a chroot cage yourself, such as
using 'mock', or are you starting with someone else's working
para-virtualized image? (See my notes above).

>> So I'm right back to my effectively unanswered original questions. So
>> please: I asked a very specific pair of questions, and they remain
>> unanswered. CentOS 5 Xen server (hypervisor, or Dom0, whatever we want
>> to call it this week): Does CentOS 6 work, paravirtualized, on such a
>> server?
> Yes, I have done that until I upgraded the CentOS 5 host to CentOS 6 a
> couple years ago.

Thanks! THAT is one of the questions I really wanted an answer for.

>> And given my deployment issues, does anyone have a base OS
>> image I can get a copy of?
> Sorry my image templates that I use are highly customized for my own
> work, but I have told you three different ways to accomplish it above.

Well, dang!