Xen users - Oct 2007 - Install 32-bit Debian DomU on 64-bit Dom0

Forgive me in advance for being both a Linux and Xen newbie...

We have a dev machine that is 64-bit AMD running Debian (etch) on Dom0, and
we''d like to have a DomU running an 32-bit i386 Debian Etch (so we can
move
it to a production machine later which is 32-bit i386). Anyhow, I''m
wondering what, if any, is the easiest path to getting this to work. From
what I''ve read, it seems a 32-bit OS can be installed on AMD-64, but
I''m not
sure the steps involved to get this working with Debian and Xen.

Thanks!


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Do you want to run the guest as PV or HVM?  64-bit Xen 3.1 can do either.  
Earlier 64-bit Xens will only support a 32-bit guest in HVM mode.

Cheers,
Mark

On Wednesday 10 October 2007, eugene smithers wrote:
> Forgive me in advance for being both a Linux and Xen newbie...
>
> We have a dev machine that is 64-bit AMD running Debian (etch) on Dom0, and
> we''d like to have a DomU running an 32-bit i386 Debian Etch (so we
can move
> it to a production machine later which is 32-bit i386). Anyhow,
I''m
> wondering what, if any, is the easiest path to getting this to work. From
> what I''ve read, it seems a 32-bit OS can be installed on AMD-64,
but I''m
> not sure the steps involved to get this working with Debian and Xen.
>
> Thanks!


-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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HVM is fine.

On 10/10/07, Mark Williamson <mark.williamson@cl.cam.ac.uk>
wrote:
>
> Do you want to run the guest as PV or HVM?  64-bit Xen 3.1 can do either.
> Earlier 64-bit Xens will only support a 32-bit guest in HVM mode.
>
> Cheers,
> Mark
>
> On Wednesday 10 October 2007, eugene smithers wrote:
> > Forgive me in advance for being both a Linux and Xen newbie...
> >
> > We have a dev machine that is 64-bit AMD running Debian (etch) on
Dom0,
> and
> > we''d like to have a DomU running an 32-bit i386 Debian Etch
(so we can
> move
> > it to a production machine later which is 32-bit i386). Anyhow,
I''m
> > wondering what, if any, is the easiest path to getting this to work.
> From
> > what I''ve read, it seems a 32-bit OS can be installed on
AMD-64, but I''m
> > not sure the steps involved to get this working with Debian and Xen.
> >
> > Thanks!
>
>
>
> --
> Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
> Mark: To answer a question with a question: What use is a skateboard?
> Dave: Skateboards have wheels.
> Mark: My wheel has a wheel!
>

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OK, well if you''re installing for HVM, then...

This is just a high-level overview.  I may have made the odd mistake or 
omission; I know I deliberately didn''t mention a few other possible
options
at various stages that we could explore if necessary.  I hope this gives you 
an idea of where you''re headed!
> > > what I''ve read, it seems a 32-bit OS can be installed on
AMD-64, but
> > > I''m not sure the steps involved to get this working with
Debian and
> > > Xen.
As I understand it, just booting a 32-bit OS install CD under HVM should do 
the job.  I think there is a config file option that allows you to choose 
whether you enable 32-bit, 32-bit PAE or 64-bit support to the guest.  I 
assume this has a sensible default of letting the guest do what it wants, 
though!

You might want to think about using a 32-bit vs 32-bit PAE install in the 
virtual machine.  A 64-bit Xen host will support either.  A 32-bit PAE Xen 
host will support either.  A 32-bit non-PAE host will only support non-PAE 
guests.  So how you should set up the guest does depend on what the 
capabilities of the 32-bit production machine are going to be.

That said, in most distros there is a choice of PAE and non-PAE kernels, and 
switching between them is as simple as installing a package and changing your 
grub config to boot the new kernel.  So don''t worry about it too much -
you
won''t be locked in ;-)

Anyhow, get an ISO image of the install CD for your 32-bit guest OS.  Create a 
virtual disk image to install to (e.g. qemu-img is a handy tool for this).  
Then create an HVM config file for the new guest based on 
the /etc/xen/xmexample.hvm file supplied with your Xen install.

You''ll want to give it a virtual CD-ROM device, pointing to the ISO
file.  And
add a disk entry for the hard drive image you just created.  Set a sensible 
name, amount of memory, and give it a virtual network interface if desired.  
You''ll need to set up a display for the guest''s framebuffer;
using the SDL
display is most straightforward.

Set the boot drive to "d" so that the domain will boot from the CD-ROM
to
start with.

Use xm create to start the domain; the sdl window should pop up showing the 
guest''s "screen".  It''ll boot off your install CD. 
Run through the normal
install.  When the install is complete and you need to boot off the hard 
drive, you''ll have to xm destroy the domain (after letting it shut down
cleanly, of course!) then modify the config file to have "c" as the
boot
drive.  Then xm create it again, and it should boot off the hard drive.

You''ll find there''s also some information in the mailing list
archives and on
the Xen wiki (in both cases, not guaranteed complete / accurate, but should 
still give you a decent idea of what''s going on!).  And if you have
more
questions / problems then folks on this list ought to be able to help you out 
some.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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