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Re: [Xen-users] Creating a paravirtualized guest with Xen 3.4.1 andCento

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Creating a paravirtualized guest with Xen 3.4.1 andCentos 5.3 (64bit)
From: Martin Troester <TroyMcClure@xxxxxx>
Date: Wed, 23 Sep 2009 22:29:59 +0200
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thanks for the steps to move an existing physical image to a paravirt DomU image. However, I think this only works if both Dom0 and DomU use the same architecture (64bit e.g.). In my case, my host is a 64bit Dom0 with 32bit DomU guests, so I think it's at least necessary to get 32bit kernel and initrd images someplace. Is there an official way to get the released 32bit xen kernel versions to be used on a 64bit host? Otherwise there's no problem to get them manually, but that means not getting auto-updates...

In addition, I found some comments on the list about CentOS 5.3 initrd images coming with scsi modules, and thus not working without rebuilding or manually changing to disable scsi.

Therefore I did the following steps to get an HVM VM initially transformed to PV:

1) get a known-good Centos image for Xen, e.g. at http://stacklet.com/downloads/images/centos/5.3
2) make sure that image works for you with pygrub
3) extract kernel, initrd and /lib/modules/
3) make it work with kernel/initrd/parameters provided externally
3a) don't use a wrong option for ramdisk support ;-)
4) add /lib/modules extracted from other image to HVM image
5a) add kernel parameter "console=/dev/tty" to prove it boots up
5b) modify /etc/securetty and /etc/inittab (if not done yet by your distro), see
6) boot up the HVM VM in paravirtualized mode

Especially 5) caused me some trouble, as without this option in /etc/inittab, the VM just froze before bringing the login prompt.

This is how far I got in a few hours tonight, but now the previously automatically launching X server does not start. Well, but I'm getting closer.

Open question:
- how to get a Centos 32bit Xen DomU kernel on a 64bit host via repositories?

Ultimatively, it will probably be best to use pygrub and do the kernel management from inside the VM (this will also be easier when thinking about /lib/modules). But at least for my VM, the harddisk layout does not work with pygrup (yet).


Jeff Sturm wrote:
-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-
bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Martin Troester
Sent: Tuesday, September 22, 2009 4:17 PM
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Creating a paravirtualized guest with Xen
3.4.1 andCentos
5.3 (64bit)

Now I'll find out if I can get my original problem solved, migrate the
existing fully virtualized system to a paravirtualizded kernel. Let's

It's not exactly the same, but I have done physical-to-paravirt
migrations on CentOS 5.2 with little effort.  It's probably easiest if
you install kernel-xen packages before you migrate:

1) yum install kernel-xen
2) shutdown
3) copy disk images to dom0
4) create domU config
5) start domU

Afterwards you can use either pygrub or kernel/ramdisk, whichever you


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