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I wanted to install a Fedora 13 machine as a paravirtual domu guest on our CentOS 5.5, xen 3.4.2 host. I also wanted to provision it using koan/cobbler. I ran into a few problems along the way, but I got there in the end!

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I needed to check the integrity of the file systems on several xen domU guests while the guests were shutdown, ie. I needed to do it from the dom0.

I use LVM logical volumes for the block devices for the guests disks named $host-disk0. These are stored in a volume group named vg_guests. I use kpartx to access the partitions on the block device.

Each guest disk has a small physical partition for /boot; the rest of the disk is allocated to a 2nd partition which is used as an LVM volume group named vg_$host.

Here's a script I knocked up to do the job:

for host in host1 host2 host3 ; do
    # create devices from the LVs
    kpartx -av /dev/mapper/vg_guests-$host--disk*
 
    # Activate the VGs for the host
    for vg in $(vgs --noheadings | grep $host | awk '{print $1}' ) ; do
        echo Activating $vg
        vgchange -ay $vg
    done
 
    # check the file systems
    for p in $(/dev/mapper/vg_$host* | grep -v swap); do
        e2fsck -p $p
    done
 
    # Deactivate the VGs
    for vg in $(vgs --noheadings | grep $host | awk '{print $1}' ) ; do
        echo De-activating $vg
        vgchange -an $vg
    done
 
    # Remove the devices
    kpartx -dv /dev/mapper/vg_guests-$host--disk0
done