Disable Apparmor:

/etc/init.d/apparmor stop
update-rc.d -f apparmor remove

AppArmor is a kernel enhancement to confine programs to a limited set of resources. AppArmor’s unique security model is to bind access control attributes to programs rather than to users.

Install XEN:

apt-get install ubuntu-xen-server
After installation of xen you should edit xorg.conf file.
vim /etc/X11/ xorg.conf

Your original xorg.conf files looks
Section "Device"
Identifier "Configured Video Device"

Now add the following line in xorg.conf

Section "Device"
Identifier "Configured Video Device"
Driver "i810"

Note: Here i810 refers to graphics chipset.So check out your system graphics chipset.

Download 2.6.24-16-xen kernel To avoid network problem:

wget http://www.il.is.s.u-tokyo.ac.jp/~hiranotaka/linux-image-2.6.24-16-xen_2.6.24-16.30zng1_i386.deb

Replace the Ubuntu 2.6.24-16-xen kernel:

dpkg -i linux-image-2.6.24-16-xen_2.6.24-16.30zng1_i386.deb

Reboot your system

Move tls file

mv /lib/tls /lib/tls.disabled

Modify Modules:

Add the line in vim /etc/modules
loop max_loop=64

Directory for XEN

mkdir /home/xen

Modify xen-tools.conf

vim /etc/xen-tools/xen-tools.conf

install-method = debootstrap # method will change with respect to type of OS
dir = /home/xen
dhcp = 1
dist = hardy # Type of guest os
passwd = 1
mirror = http://10.0.2.2:9999/ubuntu/

Reboot your system

Now Run

ubuntulinux@linux:~$ uname -r
2.6.24-16-xen
ubuntulinux@linux:~$

Create Guest OS:

ubuntulinux@linux:~$ xen-create-image --hostname=Guestos --ide --passwd

Note: You can give size, swap, Network settings, etc... to override settings in xen-tools.conf.For more details

ubuntulinux@linux:~$ man xen-create-image

After creating image file,Terminal will show message as :

Logfile produced at:
/var/log/xen-tools/Guestos.log

Guestos.cfg

vim /etc/xen/Guestos.cfg

kernel = '/boot/vmlinuz-2.6.24-16-xen'
ramdisk = '/boot/initrd.img-2.6.24-16-xen'
memory = '128'
vcpus = '2' #For dual-core CPU
root = '/dev/hda2 ro'
disk = [
'tap:aio:/home/xen/domains/Guestos/swap.img,hda1,w',
'tap:aio:/home/xen/domains/Guestos/disk.img,hda2,w',
]
vif = [ 'ip=10.0.3.2 mac=00:16:3E:C9:C2:6C' ]

To start the virtual machine:

xm create /etc/xen/Guestos.cfg
Using config file "/etc/xen/Guestos.cfg".
Started domain Guestos
xm console Guestos
Guestos started and it will prompt for user login.

To Stop the virtual machine:

xm shutdown Guestos
for more command see xm man

For Centos:
Download initrd.img and vmlinuz, then move in to /boot/ directory

wget http://mirror.centos.org/centos/5/os/i386/images/xen/initrd.img
wget http://mirror.centos.org/centos/5/os/i386/images/xen/vmlinuz

Mirror
http://mirror.centos.org/centos/5/os/i386/images/xen/