Re: [Xen-users] PXE installation of domU

["Karsten M. Self" <kself@xxxxxxxxxxxxx>]

on Thu, Dec 15, 2005 at 08:06:28AM -0800, Kevin Fox (kev@xxxxxxxxxxxxxxxxxxxxx) 
wrote:
> >From Brian.Lavender@xxxxxxxxxxxxx Wed Dec 14 19:46:17 2005
> > 
> > On Tue, 2005-12-13 at 12:22 -0800, Kevin Fox wrote:
> > > Is there a way to support the execution of a PXE installation on a newly
> > > created domU?
> > 
> > Do you mean to do an installation? I don't think you need the pxe boot.
> > You just need to boot the kernel and the ramdisk for the installer? Only
> > thing is you will have to use a Xen kernel, and then you will have to go
> > into the ramdisk and replace the modules with the modules for the Xen
> > kernel.
> 
> The intention would be a direct, non-interactive, installation from a PXE
> server.  No preinstalled image exists on the allocated drive.  Or maybe
> I'm misunderstanding your suggestion ...

PXE makes sense where you're booting from bare hardware with minimal
control over the startup process.

A Xen domU boot isn't quite equivalent to a BIOS boot.  Xen, so far as
the boot process is concerned, is more of a bootloader (GRUB/LILO)
equivalent.  What PXE provides is a way to, via the network interface,
tell the BIOS what to load.  Since Xen is already providing this
capability, PXE is not appropriate.

What you are looking for is a way to automate an install under a DomU,
initiated by Xen.  This is where Brian's ramdisk (or other initial
image) suggestion makes sense.

What you'd want to do is fire off an image (ramdisk, file-backed VBD,
whatever) with an additional VBD (the install target) specified, and use
automated install tools (KickStart, AutoYAST, FAI, etc.) to complete
your installation.

In practice, what we're seeing is creation of a library of candidate
DomU images which can be deployed simply by copying them to an
appropriate location (local storage, networked storage), or using COW
VBDs.  Deploying DomUs by way of distro installers in general isn't
necessary.


The one place I'm using PXE boots under VMs is when using qemu to
generate such image files (there's a convenience factor to this).
There's a very useful PXE floppy image available at:

    http://etherboot.anadex.de/

... which can be used via:

    qemu -fda eb_on_hd.ima -hda target.img -boot a

... where eb_on_hd.ima is the PXE floppy image and target.img is a
prepared null-filed sparse file of appropriate size:

    dd if=/dev/zero of=target.img bs=1M seek=6000 count=0

Note that this produces a partitioned image file unless you manually
specify partitioning during install.  Some distros default to LVM
configurations which throw in a few added twists.  Foregoing
partitioning an manually creating a single ext3 filesystem on /dev/hda
(_not_ /dev/hda1...) within the installer is probably your best course.

More on qemu:

    http://fabrice.bellard.free.fr/qemu/ 


Cheers.

-- 
Karsten M. Self <karsten@xxxxxxxxxxxxx>
XenSource, Inc.
2300 Geng Road #250                                +1 650.798.5900 x259
Palo Alto, CA 94303                                +1 650.493.1579 fax

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