Paravirtualization With Xen On CentOS 5.3 (x86_64)
Author: Falko Timme
Last edited 04/22/2009
This tutorial provides step-by-step instructions on how to install Xen (version 3.0.3) on a CentOS 5.3 (x86_64) system.
Xen lets you create guest operating systems (*nix operating systems like Linux and FreeBSD), so called "virtual machines" or domUs, under a host operating system (dom0). Using Xen you can separate your applications into different virtual machines that are totally independent from each other (e.g. a virtual machine for a mail server, a virtual machine for a high-traffic web site, another virtual machine that serves your customers' web sites, a virtual machine for DNS, etc.), but still use the same hardware. This saves money, and what is even more important, it's more secure. If the virtual machine of your DNS server gets hacked, it has no effect on your other virtual machines. Plus, you can move virtual machines from one Xen server to the next one.
I will use CentOS 5.3 (x86_64) for both the host OS (dom0) and the guest OS (domU).
This howto is meant as a practical guide; it does not cover the theoretical backgrounds. They are treated in a lot of other documents in the web.
This document comes without warranty of any kind! I want to say that this is not the only way of setting up such a system. There are many ways of achieving this goal but this is the way I take. I do not issue any guarantee that this will work for you!
1 Preliminary Note
This guide will explain how to set up image-based virtual machines and also LVM-based virtual machines.
Make sure that SELinux is disabled or permissive:
# This file controls the state of SELinux on the system. # SELINUX= can take one of these three values: # enforcing - SELinux security policy is enforced. # permissive - SELinux prints warnings instead of enforcing. # disabled - SELinux is fully disabled. SELINUX=disabled # SELINUXTYPE= type of policy in use. Possible values are: # targeted - Only targeted network daemons are protected. # strict - Full SELinux protection. SELINUXTYPE=targeted
If you had to modify /etc/sysconfig/selinux, please reboot the system:
2 Installing Xen
To install Xen, we simply run
yum install kernel-xen xen
This installs Xen and a Xen kernel on our CentOS system.
Before we can boot the system with the Xen kernel, please check your GRUB bootloader configuration. We open /boot/grub/menu.lst:
The first listed kernel should be the Xen kernel that you've just installed:
[...] title CentOS (2.6.18-128.1.6.el5xen) root (hd0,0) kernel /xen.gz-2.6.18-128.1.6.el5 module /vmlinuz-2.6.18-128.1.6.el5xen ro root=/dev/vg0/root module /initrd-2.6.18-128.1.6.el5xen.img [...]
Change the value of default to 0 (so that the first kernel (the Xen kernel) will be booted by default):
[...] default=0 [...]
The complete /boot/grub/menu.lst should look something like this:
# grub.conf generated by anaconda # # Note that you do not have to rerun grub after making changes to this file # NOTICE: You have a /boot partition. This means that # all kernel and initrd paths are relative to /boot/, eg. # root (hd0,0) # kernel /vmlinuz-version ro root=/dev/vg0/root # initrd /initrd-version.img #boot=/dev/hda default=0 timeout=5 splashimage=(hd0,0)/grub/splash.xpm.gz hiddenmenu title CentOS (2.6.18-128.1.6.el5xen) root (hd0,0) kernel /xen.gz-2.6.18-128.1.6.el5 module /vmlinuz-2.6.18-128.1.6.el5xen ro root=/dev/vg0/root module /initrd-2.6.18-128.1.6.el5xen.img title CentOS (2.6.18-128.el5) root (hd0,0) kernel /vmlinuz-2.6.18-128.el5 ro root=/dev/vg0/root initrd /initrd-2.6.18-128.el5.img
Afterwards, we reboot the system:
The system should now automatically boot the new Xen kernel. After the system has booted, we can check that by running
[root@server1 ~]# uname -r
So it's really using the new Xen kernel!
We can now run
to check if Xen has started. It should list Domain-0 (dom0):
[root@server1 ~]# xm list
Name ID Mem(MiB) VCPUs State Time(s)
Domain-0 0 3363 2 r----- 78.6