Although we have a number of Linux servers running on our ESX servers until recently the need had never arisen to convert an existing physical Linux server to virtual. However recently I've been doing a lot of work on using virtualization to improve Disaster Recovery options for SME clients (typically 2-25 servers), where cost is always important. Nowadays its not unusual to find networks of this size running one or two Linux boxes amongst their Windows servers but often the in-house IT only have minimal Linux admin skills.
VMware have now released Converter 4 which has support for P2V conversion of Linux systems, but only live conversion using a helper VM which has a number of drawbacks - for a start it only supports Red Hat, Suse and Ubuntu currently. My Linux guru said he wouldn't bother using any virtualization utilities but instead would backup all the config files and other data, then install the OS from scratch on a new Virtual Machine and restore the configs. I'm sure that would work but I wouldn't have a clue where to start doing that in Linux so instead I worked out a simple step-by-step process that any Windows IT person should be able to easily follow. Another important advantage of this "cold cloning" method is that no changes are made to the source Linux server as it remains offline throughout the process, so there is no risk of accidentally corrupting it.
Step One: Obtain the Required Tools
First of all this guide assumes you will be using VMware ESX3 as your virtual environment, although there is no reason you can't import your virtualized server into a VMware Server system instead. You will need an ESX server with enough free storage capacity to hold the whole capacity of your Linux server's hard disks, including free space. So if your Linux server has a 120GB RAID5 disk with 30GB of data on it you will still need to have 120GB of free space on your ESX datastore. After conversion you will be able to shrink the virtual disks to reclaim some of that space if necessary.
The conversion tool we will use is the VMware Converter 3 Enterprise BootCD, if you already have a VMware Infrastructure license or support agreement then you are entitled to download this from here. However if you are still only evaluating virtualization you can still get it - I discovered that if you register for the 60 day Infrastructure trial it enables the other downloads for you as well! Make sure you download the Zip file version of "VMware VCenter Converter 3.0.3 (Standalone Enterprise Edition)" as this also includes the BootCD image, the standard installer download does not. Once you have downloaded it just extract the ISO file, burn it to a CD and you are ready to go.