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Re: [Xen-users] Desperate :( DomU with kernel in Dom0

To: "Robin W. Muller" <robin@xxxxxxxxxxx>
Subject: Re: [Xen-users] Desperate :( DomU with kernel in Dom0
From: Nico Kadel-Garcia <nkadel@xxxxxxxxx>
Date: Sun, 28 Oct 2007 14:53:45 +0000
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
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Robin W. Muller wrote:
Hello, maybe I'm stupid but I find no way to have the kernel in Dom0 instead of DomU for Centos 5.

Here is what I did:
Regular Centos 5 Dom0 install, then creating a LVM group (vms) and install DomU with virt-install works perfectly: virt-install --p --location=http://mirrors.kernel.org/centos/5/os/i386 --file=/dev/vms/centos5_data --name=centos5 --ram=512 --nographics

I get a working domU but the config file has no kernel or ramdisk parameter and the kernel seems to be inside DomU

I created my own cfg then, using this parameter:

kernel      = '/boot/vmlinuz'
ramdisk     = '/boot/initrd.img'
root        = '/dev/xvda ro'
name = "centos"
memory = "512"
disk = [ 'phy:/dev/vms/centos_data,xvda,w', 'phy:/dev/vms/centos_swap,xvdb,w',]
vif = [ 'mac=00:64:18:20:52:07, bridge=xenbr0', ]
vcpus = 1
on_shutdown = 'destroy'
on_reboot   = 'restart'
on_crash    = 'restart'

RHEL's version of Xen uses "pygrub", a friendly tool for looking inside Xen guests and loading the boot loader from there. Despite a reported, and fixed, security issue with that approach, it's potentially really helpful not to have to the guest's kernel on your Dom0, and I recommend the practice.

For vmlinuz I tried a copy of Dom0's kernel, the kernel copied from inside the DomU as well as the downloaded kernel file from here:

You mean you installed the RPM's right?

For initrd.img I tried a copy of Dom0's ramdisk, the ramdisk copied from inside the DomU as well as the downloaded ramdisk file from kernel.org.
I even tried building a ramdisk with:

/sbin/mkinitrd /boot/initrd.img 2.6.18-8.el5xen --with=netfront --with=blkfront --with=sd_mod --with=scsi_mod

Nothing helps, the result is always:

mount: could not find filesystem '/dev/root'


switchroot: mount failed: No such file or directory

...well not always, if I use the ramdisk downloaded from kernel.org, I get a installation procedure (asking for language, skip media check and so on).

What have I done wrong?

Thank you very much for any help here!

Before exploring this, why are you doing it? Why not use the kernel from inside the DomU? That way, you can update your kernels, or use distinct ones for different CentOS purposes, such as NTFS access with the centosplus kernels.

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