Virtualize a Server with Minimal Downtime

When it's time to convert a physical machine to a virtual one, use these steps to make the move safely and with a small maintenance window.

Kyle Rankin is VP of engineering operations at Final, Inc., the author of many books including Linux Hardening in Hostile Networks, DevOps Troubleshooting and The Official Ubuntu Server Book, and a columnist for Linux Journal. Follow him @kylerankin


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Older Linux ext2/3 filesystem

Paul Schilling's picture

I was able to virtualize two older RedHat system using this method though I did run into ext2/3 filesystem issues. One system was an old RedHat 5.2 (circa 1998). I was booting the VM with Knoppix V6.0 live CD and then creating the partitions and ext2 filesystem. After rsync'ing files I found I couldn't boot. This turned out to be ext2 filesystem features. The Knoppix OS created an ext2 with all the latest features but the old RedHat 5.2 predated many of these features so it didn't know how to handle them.

I rebuilt the ext2 FS with options to turn off just about every feature.
mkfs -t ext2 -O none -r0 -O ^dir_index /dev/sdxx

Then I was able to rsync and complete all steps ending with a bootable RedHat 5.2 guest VM

Thanks for the great article.

Ubuntu 8 2.6.24 kernel I had

Pkilpo's picture

Ubuntu 8 2.6.24 kernel

I had to use "mount --bind /dev /mnt/sda1"
then chroot /mnt/sda1
then mount /proc /proc -t proc
and used mkinitramfs -o /boot/initrd.img

Filesystem has unsupported features

Len Kranendonk's picture

After migrating an old RedHat 9 server to VMWare using this howto, I got an error saying fsck.ext3: Filesystem has unsupported features.

I've posted a description on how to solve this issue on my blog: fsck: Filesystem has unsupported features.

I hope this might be helpful for people encountering the same issue.


Johannes Wolter's picture

I ran into problems because Knoppix mounted my root partition with the nodev option, which made the grub-install and mkinitrd calls fail, because the devices were not accessible. I had to change the mount-options with mount -oremount,dev,setuid /dev/sda1.
Furthermore I had a problem because /var is on a different partition (/dev/sda3)in my setup. I had to unmount this partition before chroot-ing and had to (re-)mount in the chroot-environment.

grub install issue

gc's picture

I'm having some issue with grub-install, mainly the fact that the system I'm virtualizing has a raid device for the hard drive. I've tried the grub install using some soft links to map the device names and the setup (hd0) command appears to complete but the virt-manager states the disk is not bootable

any suggestions

I had similar issues because

spingary's picture

I had similar issues because my set up has a /boot partition:

/dev/sda1 -> /boot
/dev/sda2 -> /
/dev/sda3 -> (swap)

so chroot'ing into my root, /dev/sda2, won't exactly work right since /boot is not there. Here's what I did to get it to work, using manual grub instead of grub-install:

Before you chroot into anything (while in Knoppix shell):

$ grub
grub> root (hd0,0)
grub> setup (hd0)
grub> exit

The 1st line points root to my first partition (/dev/sda1)
2nd line sets it up. What this does is set up grub on the MBR of the virtual disk.

Then, to rebuild the initrd correctly, I had to do this:

$ umount /mnt/sda1

$ mount -o remount,dev /mnt/sda2
(assuming sda2 was already mounted)
This mount command helps eliminate /dev/null problems when using the mkinitrd command later.

$ mount /dev/sda1 /mnt/sda2/boot
(This puts the boot partition into my sda2 root mount)

Now we can chroot:
$ chroot /dev/sda2
$ ls /boot
(should see the /boot partition stuff)

I had to add these to /etc/modprobe.conf in my install (I am using VMWare server 2.0.0 RC1):

alias scsi_hostadapter mptbase
alias scsi_hostadapter1 mptscsih

Now I rebuilt initrd:

Now we do the equivalent of this:

# mv /boot/initrd-2.4.21-32.0.1.ELsmp.img /boot/initrd-2.4.21-32.0.1.ELsmp.img.bak
# mkinitrd -v /boot/initrd-2.4.21-32-0.1.ELsmp.img 2.4.21-32-0.1.ELsmp
(Notice that the orig article was missing the .img in the second line)
(Also use the -v flag to see any useful errors)

I had one last problem - when I rebooted it complained the my e2fsck was too old and keep dumping me into repair mode. My install is a real old FC2, and when I used Knoppix to create the ext3 file systems, there are "new features" that the older e2fsck didn't support. So I followed these instructions and all is good:

Good luck everyone. Thank you for a great guide!

I had a problem...

Enrique Garcia's picture


Before the second and final rsync, I wanted to test if the machines goes alive, but when I do the chroot /mnt/sda, and then
# grub-install /dev/sda
it gives:
/usr/share/grub/i386-redhat/stage1: Not found

And tried:
fdisk -l (without result)

It seems that I can't have access to /var /usr /home which are other partitions

What I tried next, was to cp the files in /mnt/sda3 (/usr), to /mnt/sda1 (/) just the files in the corresponding /usr/share/grub/i386-redhat/

And the output of that command was:
/sbin/grub-install: line 501: uniq: command not found
/dev/sda: Not found or not a block device.

any advice will be greatly appreciated.

Thanks in advance.

Even though

Enrique Garcia's picture

Even though the missing -H option, this is a great HOWTO, include I will be using this to migrate from one server to other and another, obviously I had never figure it out by myself... Thank you very much, And if possible, I would like to have your agreement to translate it, (and include fdisk steps) to Spanish.


rsync and hardlinks

Thomas Mueller's picture

the rsync options "-avx --numeric-ids --progress" IMHO doesn't include "-H" (hardlinks). So if a systems uses many hardlinks there will be many duplicated files.