Anthony Liguori wrote:

Mark Williamson wrote:

I have just recently discovered the XEN VMM and am trying to familiarize

myself with it. I'm a newbe at it, so bear with me.

No probs, here goes...

I'd like to install an O/S onto a guest virtual machine. Domain 0 is RHEL4 on Xen 2.0.7. My question is how I would go about installing from a set of distribution CD's (say RHEL4 or SUSE9) into a file-backed VMM. Can anyone

help me out with this?

Installing into a file-backed VBD from a distro CD is tricky.

Actually, if you use QEMU to install the distro into a raw disk, and you only create one partition on the disk, you should be able to just use a command like this:

dd skip=63 bs=512 if=qemu.img of=xen.img
Keep in mind, I've not tried this myself :-)

Exporting the qemu image as /dev/hda in domU and just setting your parameters right seems to work well and is much simplier.

Are you doing this with the qemu partitioned file itself?
The procedure I've worked up is:
1. Create a target install file. Creating this as a sparse file saves
 blocks on disk until you actually need them:
 dd if=/dev/zero of=rhel4_qemu bs=1024k seek=$(( 6 * 1024 )) count=0
 The $(( 6 * 1024 )) gives you 6 GB to work with, the seek means it's
 sparse, and the count=0 means there's only one block used on disk
2. Install RHEL flavor of your choosing. You can boot either from an
 install CD, _or_ an ISO image corresponding to same:
 qemu -cdrom <cd drive or ISO image> -boot c rhel4_qemu
 Walk through the installation. Your image file (rhel4_qemu) will
 automatically be partitioned.
3. Shut down qemu after the install is completed.
4. Find out the image file's partitioning. fdisk's '-u' option gives
 output in sectors. This helps in the next step. Sample partition
 table:
 $ /sbin/fdisk -lu rhel4
 You must set cylinders.
 You can do this from the extra functions menu.
 Disk rhel4: 0 MB, 0 bytes
 255 heads, 63 sectors/track, 0 cylinders, total 0 sectors
 Units = sectors of 1 * 512 = 512 bytes
 Device Boot Start End Blocks Id System
 rhel4p1 * 63 208844 104391 83 Linux

 rhel4p3 401625 4192964 1895670 83 Linux
 Ignore the cylinder messages (they matter if you're going to modify
 the partition table).
 The start sector times the blocksize (512 bytes) gives you the
 partition offset in bytes. This is used if you want to loopback
 mount the filesystems to copy them someplace else, which you do.
 The first partition is /boot, the second is /. I didn't use logical
 volumes, though it's possible to do so, complicating matters
 somewhat more.
5. Loopback mount the qemu images, creating a couple of mountpoints.
 Using the file I'm referencing above (rhel4):
 mkdir mp1 mp2
 su -c 'mount -o loop,offset=$(( 63 * 512 )) -t ext3 rhel4 mp1'
 su -c 'mount -o loop,offset=$(( 4192964 * 512 )) -t ext3 rhel4 mp2'
As a final step, you could copy the contents of these two mountpoints
into a partition or a single filesystem image (a file with just a
filesystem in it, no partitions) which can be used for a Xen file-backed
DomU, etc.
You will have to modify the DomU's /etc/fstab and likely comment the MAC
address registered in /etc/sysconfig/network-scripts/ifcfg-eth0 for
things to work properly.

There are some good related docs on Fedora and Debian installs as well:
https://www.redhat.com/archives/fedora-devel-list/2005-January/msg01320.html
http://www.fedoraproject.org/wiki/FedoraXenQuickstart
Debian: http://hands.com/d-i/HOWTO-xen.txt
--
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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