Re: [Xen-users] Creating a paravirtualized guest with Xen 3.4.1 andCentos 5.3 (64bit)

[Martin Troester <TroyMcClure@xxxxxx>]

Jeff,

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
http://xen.xensource.com/files/xensummit_4/xensummit_linux_console_slides.pdf
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).
Regards,
Martin

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
> see...
>
> 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
> prefer.
>
> -Jeff

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