Re: [Xen-users] Cannot open root device

[Lyndsay Roger <gombadi@xxxxxxxxx>]

On Sun, 2005-06-05 at 10:42 +0200, Hsing-Foo Wang wrote:
> Lyndsay Roger wrote:
> > On Sun, 2005-06-05 at 10:19 +0200, Hsing-Foo Wang wrote:
> > 
> >>>I use Ubuntu and with partitions I just cp -a /* /mnt/dom1
> >>>to copy the whole thing to another partition, then change a few config
> >>>files and I have the other domains running.
> >>>Depending on the size of your disk you may be able to copy your existing
> >>>system to a file and use that as a guest.
> >>
> >>Without kernel changes?? I thought the guest OS needs be recompiled to 
> >>be used under Xen as a guest OS.
> > 
> > 
> > The guest does not use the kernel from the guest filesystem. It uses the
> > vmlinuz-2.?.??-xenU kernel from dom0 file system but it uses the modules
> > from its own file system so you need to copy
> > the /lib/modules/kernel-version modules that are supplied in the xen
> > binary package or that you complied, to the guest filesystem.
> > 
> > Hope I don't confuse things more :-)
> 
> Oh yes you did :-)
> 
> So for example i want to use Centos 3.4 as a guest OS, how would I go 
> about please? Let's say I have 1 Centos 3.4 ISO file.

Never used Centos or installed from an ISO cdrom image. With Debian
based systems you can install in a chroot environment to a particular
file system but I have never done that either :-)

What I have done is -

- Installed the minimum Ubuntu system to a machine as you normally
would. (hda1)
- tar the system to a file
- Install xen to the machine & compile so it has support for the chipset
- create another partition for the guest (hda2) system & untar the file
created above
- chroot to the new partition (hda2) & un-install the kernel packages
- edit the files on hda2 to change hostname, ip address etc
- create a config file, on dom0(hda1), for the guest which maps hda2 on
dom0 to be hda1 on the guest
- xm create /path/to/config/file and the guest should boot & run
- guest uses kernel from dom0 (hda1) but sees what it thinks is hda1
(but is actually hda2) as its root file system

The result is I have a 67MB tar.gz file that contains a base Ubuntu
system so if I want another guest I just create a partition, untar the
file, edit the config files and boot another guest system. 
I should, but have not tried yet, be able to untar the base system file
to a file mounted on a loop mount point & create a system that uses a
file on dom0 instead of a separate partition for the guests. (like the
xen example using ttylinux)

I have the advantage of having a different system to test on and can
therefore install a system from scratch. It makes life a bit easier :-)

Others may be able to provide help installing a guest from an ISO image
file.

Have I made you more confused :-)


Lyndsay.



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