Help needed running an X11 environment inside a DomU (Re: [Xen-users] Creating a paravirtualized guest with Xen 3.4.1 andCentos 5.3 (64bit))

[Martin Troester <TroyMcClure@xxxxxx>]

Hi all,

looks I am somewhat stuck with getting X11 to run inside a DomU. 
Searching for this gives me only little help. As far as I understand, it 
does not work out of the box because there is on real graphics hardware 
available. That definitely explains the output of the X server, 
complaining about not finding any screens to use.
One thing seems to be provide an external framebuffer, as described 
here: http://wiki.xensource.com/xenwiki/VirtualFramebuffer
This page is dated Feb 2008, so is there any important news about this? 
The last line is most discouraging to me, is there any interesting 
updates regarding desktop size? What about performance? Well, I'll try 
that now anyway.
In addition, as the VM runs fine in HVM (including X), is there any way 
to configure an emulated graphics device for a pv DomU? Reads strange... 
But with graphics hardware not being virtualizable, something like this 
would help.
Any hints/links/documentation on my problem is really appreciated.

Thanks!

Regards,
Martin

Martin Troester wrote:
> 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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