Introduction to Hypervisors Download PDF
A hypervisor can be defined as a piece of software, firmware or hardware that can run Virtual Machines. There are two types of hypervisors Type 1 and Type 2.
A hypervisor can be defined as a piece of software, firmware or hardware that can run Virtual Machines. There are two types of hypervisors Type 1 and Type 2.
Type 1 Hypervisors(Fig. 1): These types of hypervisors run just above the hardware layer and has direct access to the hardware and are also called Bare-Metal Hypervisors. Thus the guest OS runs on a level above the hypervisor. The examples of these types of hypervisors are Xen, Citrix XenServer(commercial alternative to Xen), Microsoft Hyper-V, etc.
Type 2 Hypervisors(Fig. 2): These type of hypervisors run within a conventional Operating System environment and are also called Hosted hypervisors. The examples of these types of hypervisors are VMWare Workstation, VirtualBox, etc.
These hypervisors provide a layer of hardware virtualization through which multiple OS can simultaneously. In this article I will explain on Type 1 or Bare-Metal hypervisors.
Type 1 Hypervisors
These hypervisors run just above the hardware and try to implement the basic layer of hardware virtualization. A number of guest OS can be made to run simultaneously on these type of hypervisors. The guest OS interacts with these hypervisors to do its various tasks like interfacing with the hardware devices or to allocate memory and control the processor execution.
Hypervisors provide a layer of separation between different guest OS so that the guest OS can run independently. There are mainly two types of virtualizations possible using Type 1 Hypervisors namely 1). ParaVirtualization and 2). Full Virtualization.
Xen: A powerful hypervisor
Xen is a hypervisor providing services that allows multiple computer operating systems to execute on the same hardware concurrently.
Xen is a powerful hypervisor capable of running many different types of guest OS like linux, netBSD, Solaris and Microsoft Windows.
Xen is a bare-metal hypervisor which provides a layer to the Guest OS for interfacing with the hardware.
Xen is capable of providing both para-virtualization and full virtualization. For Full Virtualization their should be Hardware-assisted Virtualization support.
Xen also supports live migration from one OS to another and aims to provide 0 downtime in migration. For this Xen loads all the OS address space in the memory so switching can be ultra-fast.
System Requirements for Xen:
Processor: 64-bit processor with minimum clock speed of 1.5 Ghz with Intel VT or AMD-V for Full Virtualization
Ram: 1 GB (minimum), 2GB or more (Recommended)
Disk Space: 16GB (minimum), 60GB or more(Recommended)
A little explanation?
Now, we will know how to set dom0 and domU on Ubuntu 12.10.
Lets first know what exactly are these dom0 and domU.
Dom0
dom0 is the initial domain that is started by the Xen Hypervisor on boot. Without this the Xen hypervisor is just useless.
Dom0 is essentially the host operating system on which Xen hypervisor run Xen Mangement toolstack and has special privileges, like being able to access the hardware directly.
DomU
domU is the counterpart to dom0. It has no special privileges and can not interface the hardware directly. The kernel of domU comes from dom0 ‘s filesystem, not from filesystem exported to domU.
Now when we know what are dom0 and domU, lets have a look on how to install Xen as dom0 and domu on Ubuntu 12.10.
Installing Xen as dom0 and domU on Ubuntu
Installing Xen dom0 and domU on Ubuntu is very much easier. Lets have a look how to do it.Open terminal in Ubuntu by pressing Ctrl+Alt+T and follow this guide.
Step 1: Write the following command in the terminal Running this command you will prompted to enter your password. Enter it and Ubuntu will ask you whether you want to install it or not. Just Press Y followed by Enter.
Step 2: Now all the required packages have been installed. Now you need to run your dom0. For this you will have to restart your system. But wait… there is one thing left. We need to edit a file “/etc/xen/xend-config.sxp”. For this run this command
sudo gedit /etc/xen/xend-config.conf
restart and choose Ubuntu with Xen Hypervisor from GRUB boot menu.
Step 3: Now you will be in Ubuntu running with Xen hypervisor. Now lets proceed. Now use this command and you will see your system running.
Step 4: Now lets create a domU. First we need to configure a file“/etc/xen-tools/xen-tools.conf”. For this execute this command.
sudo gedit /etc/xen-tools/xen-tools.conf
Now find these enteries in this file and chnage them as given here. If these enteries are preceeded by # remove the hashes
dir=/mnt/xen
This command will set the directory where Xen will mount the guest OS
install-method=debootstrap
This method tells how to install the guest OS
size=8Gb
This will set the disk image size
memory=1024Mb
This sets the amount of memory available to guest OS
swap=128Mb
This sets the disk space available as swap
fs=ext3
This sets the type of filesystem for the disk image
dist=lucid
This sets the default distribution to install
image=sparse
This sets the type of image to be used
dhcp=1
This sets the dynamic IP allocation for guest OS
nameserver=< IP address of the DNS server>
If this property is not set then the configuration for this will be taken from host OS
bridge=virbr0
This sets the bridge mode
kernel = /boot/vmlinuz-`uname -r`
This will set the kernel for the guest OS
initrd = /boot/initrd.img-`uname -r`
This will set the initial ramdisk file for the guest OS
mirror = http://archive.ubuntu.com/ubuntu
This will set the place from where the guest OS is downloaded
ext3_options = noatime,nodiratime,errors=remount-ro
ext2_options = noatime,nodiratime,errors=remount-ro
These two commands sets the filesystem options
xfs_options = defaults
reiserfs_options = defaults btrfs_options = defaults
These two commands sets the filesystem options
boot = 1 passwd = 1
serial_device = hvc0 disk_device = xvda
Step 5: Now we are 90% done with our work. Now lets complete the remaining 10% and take some rest.
Now lets create the image. Issue this command to create the image
sudo xen-create-image –hostname=ubuntu10
When your image is being created it may ask for root password. Just provide any password and your domain will start automatically.
Step 6: Now you can login to it using
xm console ubuntu10
to terminate
xm destroy ubuntu10
to restart
xm create -c /etc/ubuntu10.cfg
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