Virtualization With Xen On CentOS 6.2 (x86_64) (Paravirtualization & Hardware Virtualization)

This tutorial provides step-by-step instructions on how to install Xen (version 4.1.2) on a CentOS 6.2 (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 6.2 (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 Creating A Network Bridge

We need to set up a network bridge on our server so that our virtual machines can be accessed from other hosts as if they were physical systems in the network.
To do this, we install the package bridge-utils...
... and configure a bridge. Create the file /etc/sysconfig/network-scripts/ifcfg-br0 (please use the IPADDR, PREFIX, GATEWAY, DNS1 and DNS2 values from the /etc/sysconfig/network-scripts/ifcfg-eth0 file); make sure you use TYPE=Bridge, not TYPE=Ethernet:

DEVICE="br0" NM_CONTROLLED="yes" ONBOOT=yes TYPE=Bridge BOOTPROTO=none IPADDR=192.168.0.100 PREFIX=24 GATEWAY=192.168.0.1 DNS1=8.8.8.8 DNS2=8.8.4.4 DEFROUTE=yes IPV4_FAILURE_FATAL=yes IPV6INIT=no NAME="System br0"

Modify /etc/sysconfig/network-scripts/ifcfg-eth0 as follows (comment out BOOTPROTO, IPADDR, PREFIX, GATEWAY, DNS1, and DNS2 and add BRIDGE=br0):

DEVICE="eth0" NM_CONTROLLED="yes" ONBOOT=yes HWADDR=00:1E:90:F3:F0:02 TYPE=Ethernet #BOOTPROTO=none #IPADDR=192.168.0.100 #PREFIX=24 #GATEWAY=192.168.0.1 #DNS1=8.8.8.8 #DNS2=8.8.4.4 DEFROUTE=yes IPV4_FAILURE_FATAL=yes IPV6INIT=no NAME="System eth0" UUID=5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03 BRIDGE=br0

Restart the network...
... and run
It should now show the network bridge (br0):
 

3 Installing Xen

First check if your CPU supports hardware virtualization - if this is the case, the command
should display something, e.g. like this:
If nothing is displayed, then your processor doesn't support hardware virtualization. This means you can use only paravirtualization with Xen, but not hardware virtualization.
As CentOS 6 is based on RedHat 6, and RedHat has dropped support for Xen in version 6, we need to get Xen from a third-party repository. We can enable the repo as follows:
To install Xen, we now simply run
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 (2.6.32.54-1.el6xen.x86_64) root (hd0,0) kernel /vmlinuz-2.6.32.54-1.el6xen.x86_64 ro root=/dev/mapper/VolGroup00-LogVol00 rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD quiet SYSFONT=latarcyrheb-sun16 rhgb crashkernel=auto KEYBOARDTYPE=pc KEYTABLE=de rd_LVM_LV=VolGroup00/LogVol01 rd_LVM_LV=VolGroup00/LogVol00 rd_NO_DM initrd /initramfs-2.6.32.54-1.el6xen.x86_64.img [...]

We need to modify that section so that the Xen hypervisor gets loaded first. In the kernel /vmlinuz... line, replace the first word kernel with module. Do the same in the next line - replace the first word initrd with module in the initrd /initramfs... line. Then add the line kernel /xen.gz dom0_mem=1024M cpufreq=xen dom0_max_vcpus=1 dom0_vcpus_pin after the root line and before the first module line (if you have more than one CPU core, you can specify another number than 1 for dom0_max_vcpus). The final kernel section should look like this:

[...] title CentOS (2.6.32.54-1.el6xen.x86_64) root (hd0,0) kernel /xen.gz dom0_mem=1024M cpufreq=xen dom0_max_vcpus=1 dom0_vcpus_pin module /vmlinuz-2.6.32.54-1.el6xen.x86_64 ro root=/dev/mapper/VolGroup00-LogVol00 rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD quiet SYSFONT=latarcyrheb-sun16 rhgb crashkernel=auto KEYBOARDTYPE=pc KEYTABLE=de rd_LVM_LV=VolGroup00/LogVol01 rd_LVM_LV=VolGroup00/LogVol00 rd_NO_DM module /initramfs-2.6.32.54-1.el6xen.x86_64.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/mapper/VolGroup00-LogVol00 # initrd /initrd-[generic-]version.img #boot=/dev/sde default=0 timeout=5 splashimage=(hd0,0)/grub/splash.xpm.gz hiddenmenu title CentOS (2.6.32.54-1.el6xen.x86_64) root (hd0,0) kernel /xen.gz dom0_mem=1024M cpufreq=xen dom0_max_vcpus=1 dom0_vcpus_pin module /vmlinuz-2.6.32.54-1.el6xen.x86_64 ro root=/dev/mapper/VolGroup00-LogVol00 rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD quiet SYSFONT=latarcyrheb-sun16 rhgb crashkernel=auto KEYBOARDTYPE=pc KEYTABLE=de rd_LVM_LV=VolGroup00/LogVol01 rd_LVM_LV=VolGroup00/LogVol00 rd_NO_DM module /initramfs-2.6.32.54-1.el6xen.x86_64.img title CentOS (2.6.32-220.el6.x86_64) root (hd0,0) kernel /vmlinuz-2.6.32-220.el6.x86_64 ro root=/dev/mapper/VolGroup00-LogVol00 rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD quiet SYSFONT=latarcyrheb-sun16 rhgb crashkernel=auto KEYBOARDTYPE=pc KEYTABLE=de rd_LVM_LV=VolGroup00/LogVol01 rd_LVM_LV=VolGroup00/LogVol00 rd_NO_DM initrd /initramfs-2.6.32-220.el6.x86_64.img

Before we reboot, we install the libvirt and python-virtinst (which contains the virt-install tool which we will use later on to install Xen VMs) packages:
Because the libvirt package from CentOS 6/RedHat 6 has no support for Xen, we must rebuild it with Xen support. To do this, we install a few prerequisites now:
Let's find out our libvirt version:
It's 0.9.4, so we download the appropriate src.rpm package into /root/src and install it:
The last command will show some warnings that you can ignore:
Next we patch Xen support into the libvirt sources:
Now we build a new libvirt package:
At the end of the build process you should see something like this:
Go to the directory where the new packages have been created (/root/rpmbuild/RPMS/x86_64/ in this case)...
... and install the new libvirt packages (with Xen support) as follows:
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
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):
Instead of using the xm command, I will from now on use the virsh command to manage Xen VMs. This is the preferred way as we are using libvirt.
should show this:

4 Paravirtualization

4.1 Creating An Image-Based Virtual Machine

We will create our image-based virtual machines in the directory /var/lib/libvirt/images/ which was created automatically when we installed libvirt.
CentOS has a nice tool called virt-install with which we can create virtual machines for Xen. To start it, we simply run
(We must specify our network bridge with --network bridge=br0 so that the virtual machine uses our network bridge which we created in chapter2.)
The tools asks a few questions before it creates a virtual machine. I want to call my first virtual machine vm01, with 1024MB RAM and a disk size of 10GB. I want to store it in the file /var/lib/libvirt/images/vm01.img:
Would you like a fully virtualized guest (yes or no)? This will allow you to run unmodified operating systems.
<-- no
What is the name of your virtual machine?
<-- vm01
How much RAM should be allocated (in megabytes)?
<-- 1024
What would you like to use as the disk (file path)?
<-- /var/lib/libvirt/images/vm01.img
How large would you like the disk (/vm/vm01.img) to be (in gigabytes)?
<-- 10
What is the install URL?
<-- http://ftp.tu-chemnitz.de/pub/linux/centos/6.2/os/x86_64
In this chapter I want to create a paravirtualized guest, not a fully (hardware) virtualized guest, that's why I answer the first question with no.
As install URL, you should specify a mirror close to you where the installer can download all files needed for the installation of CentOS 6.2 in our virtual machine. You can find a list of CentOS mirrors here: http://www.centos.org/modules/tinycontent/index.php?id=13
After we have answered all questions, virt-install starts the normal CentOS 6.2 installer (in text mode) in our vm01 virtual machine. After a few moments the installer gives you the choice to use VNC or to continue with the text mode installer. Using text mode is no problem if you are familiar with the CentOS installer, but if you like a little more comfort, select Start VNC here:


On the next screen you can provide a password for the VNC connection (recommended). IF you don't want to use a password, hit No password:


Afterwards, the installer tells you how you can connect to the installer via VNC (192.168.0.15:1 in this case):


Now open a VNC client (like TightVNC) and type in the connection details (192.168.0.15:1 in this case) and click on Connect:

If you have specified a password for the VNC connection, you must now provide it:

Afterwards you can use the CentOS installer in your VNC client:


After the installation, we stay at the vm01 console. To leave it, type CTRL+] if you are at the console, or CTRL+5 if you're using PuTTY. You will then be back at the dom0 console.
Run
to log in on that virtual machine again (type CTRL+] if you are at the console, or CTRL+5 if you're using PuTTY to go back to dom0), or use an SSH client to connect to it.
To get a list of running virtual machines, type
The output should look like this:
To shut down vm01, do this:
To start vm01 again, run
Here are the most important Xen commands:
virsh start - Start a virtual machine.
virsh shutdown - Stop a virtual machine.
virsh destroy - Stop a virtual machine immediately without shutting it down. It's as if you switch off the power button.
virsh list - List all running systems.
virsh console - Log in on a virtual machine.
virsh help - List of all commands.

4.2 Creating An LVM-Based Virtual Machine (Paravirtualization)

This chapter explains how you can set up LVM-based virtual machines instead of virtual machines that use disk images. Virtual machines that use disk images are very slow and heavy on disk IO.
In this example I'm using a CentOS 6.2 host with the LVM volume group /dev/VolGroup00 that has about 465GB of space. /dev/VolGroup00 contains two logical volumes, /dev/VolGroup00/LogVol00 and /dev/VolGroup00/LogVol01 that consume about 104GB of space - the rest is not allocated and can be used to create logical volumes for our virtual machines:
I want to create the virtual machine vm02 now which uses the logical volume /dev/VolGroup00/vm02. I want the virtual machine to have a disk space of 10GB, so I create the logical volume /dev/VolGroup00/vm02 as follows:
Afterwards we can run
again:
Would you like a fully virtualized guest (yes or no)? This will allow you to run unmodified operating systems.
<-- no
What is the name of your virtual machine?
<-- vm02
How much RAM should be allocated (in megabytes)?
<-- 1024
What would you like to use as the disk (file path)?
<-- /dev/VolGroup00/vm02
What is the install URL?
<-- http://ftp.tu-chemnitz.de/pub/linux/centos/6.2/os/x86_64
As the disk file path, we specify our new volume group /dev/VolGroup00/vm02. Please note that virt-install doesn't ask for the disk space anymore because the disk space is determined by the size of the logical volume (10GB).

4.3 Using virt-manager To Create & Manage Virtual Machines

Instead of using VNC or a text-based installer, we can use virt-manager on a Linux desktop to create and manage virtual machines. In this example, I'm using a Fedora 16 desktop.
Initialize a new VM on the CentOS 6.2 host (in this example, it's vm06):
The --vnc --noautoconsole parameters are important - they allow us to connect to the installer with virt-manager.
[root@server1 ~]# virt-install --prompt --network bridge=br0 --virt-type=xen --vnc --noautoconsole
Would you like a fully virtualized guest (yes or no)? This will allow you to run unmodified operating systems.
<-- no
What is the name of your virtual machine?
<-- vm06
How much RAM should be allocated (in megabytes)?
<-- 1024
What would you like to use as the disk (file path)?
<-- /var/lib/libvirt/images/vm06.img
How large would you like the disk (/var/lib/libvirt/images/vm06.img) to be (in gigabytes)?
<-- 10
What is the install URL?
<-- http://ftp.tu-chemnitz.de/pub/linux/centos/6.2/os/x86_64
As you see the command returns to the prompt, so we must use virt-manager now to complete the VM installation.
You can install virt-manager as follows on a Fedora 16 desktop - open a terminal and become root:
Then install virt-manager:
Go to Applications > System Tools > Virtual Machine Manager to start virt-manager:

When you start virt-manager for the first time, you will most likely see the following message (Packages required for KVM usage). You can ignore this because we don't want to connect to the local libvirt daemon, but to the one on our CentOS 6.2 Xen host. Click on No...


... and go to File > Add Connection... to connect to our CentOS 6.2 Xen host:


Select Xen as Hypervisor, then check Connect to remote host, select SSH in the Method drop-down menu, type in root as the Username and the hostname (server1.example.com) or IP address (192.168.0.100) of the CentOS 6.2 Xen host in the Hostname field. Then click on Connect:


If this is the first connection to the remote Xen server, you must type in yes and click on OK:


Afterwards type in the root password of the CentOS 6.2 Xen host:


You should see vm06 as running. Mark that guest and click on the Open button to open the graphical console of the guest:


Type in the root password of the Xen host again:


You should now be connected to the graphical console of the guest and see the CentOS installer:




Now install CentOS as you would normally do on a physical system. Please note that at the end of the installation, the CentOS guest needs a reboot. The guest will then stop, so you need to start it again, either with virt-manager or like this on our CentOS 6.2 Xen host command line:
Afterwards, you can connect to the guest again with virt-manager and configure the guest. If you install OpenSSH in the guest, you can connect to it with an SSH client (such as PuTTY).

5 Full Virtualization (Hardware Virtualization)

The process for creating a fully virtualized guest is not that much different from that for creating a paravirtualized guest, except that for full virtualization, you need virt-manager (installation cannot be completed on the command line) and installation media (CD/DVD or an .iso image).

5.1 Creating A Fully Virtualized Guest On The Command Line

Because we need installation media, you can now either put your CentOS 6.2 DVD (the first one) into your DVD drive, or you download the CentOS 6.2 iso file and put it in the /var/lib/libvirt/images/ directory (it must be in the /var/lib/libvirt/images/ directory because later on I will show how to create virtual machines through virt-manager from your Fedora desktop, and virt-manager will look for ISO images in the /var/lib/libvirt/images/ directory). IT is also possible to create an iso file from the DVD as follows:
The guest installation can be started as follows:
[root@server1 ~]# virt-install --prompt --network bridge=br0 --virt-type=xen --vnc --noautoconsole
Would you like a fully virtualized guest (yes or no)? This will allow you to run unmodified operating systems.
<-- yes
What is the name of your virtual machine?
<-- vm03
How much RAM should be allocated (in megabytes)?
<-- 1024
What would you like to use as the disk (file path)?
<-- /var/lib/libvirt/images/vm03.img (you can as well specify a logical volume here, see chapter 4.2)
How large would you like the disk (/var/lib/libvirt/images/vm03.img) to be (in gigabytes)?
<-- 10
What is the install CD-ROM/ISO or URL?
<-- /dev/cdrom (you can also specify an iso file here, e.g. /var/lib/libvirt/images/CentOS-6.2-x86_64-bin-DVD1.iso)
That's it! Now you must open virt-manager and complete the guest installation, as shown in chapter 4.3.

5.2 Creating A CentOS 6.2 Guest (Image-Based) From The Desktop With virt-manager

Instead of creating a virtual machine from the command line, you can as well create it from the Fedora desktop using virt-manager (of course, the virtual machine will be created on the CentOS 6.2 Xen host - in case you ask yourself if virt-manager is able to create virtual machines on remote systems).
(I have tried this for a paravirtualized guest as well, but got an error after initrd.img got loaded - therefore this chapter is only for fully-virtualized guests.)
To do this, click on the following button:

The New VM dialogue comes up. Fill in a name for the VM (e.g. vm07), select Local install media (ISO image or CDROM), and click on Forward:


Next check Use ISO image and click on the Browse... button:


Select the CentOS-6.2-x86_64-bin-DVD1.iso image and click on Choose Volume:


Now select Linux in the OS type drop-down menu and RedHat Enterprise Linux 6 in the Version drop-down menu, then click on Forward:


Assign memory and the number of CPUs to the virtual machine and click on Forward:


Now we come to the storage. Check Enable storage for this virtual machine, select Create a disk image on the computer's hard drive, specify the size of the hard drive (e.g. 10GB), and check Allocate entire disk now. Then click on Forward:


Now we come to the last step of the New VM dialogue. Go to the Advanced options section. Select Specify shared device name and then specify br0 in the Bridge name field; that is the name of the bridge which we created in chapter 2. Click on Finish afterwards:


The disk image for the VM is now being created:


Afterwards, the VM will start. Type in the root password of the CentOS 6.2 Xen host:


You should now be connected to the graphical console of the guest and see the CentOS installer:


Now install CentOS as you would normally do on a physical system.

6 Managing A Xen Guest From The Command Line

Xen guests can be managed through virsh, the "virtual shell". To connect to the virtual shell, run
This is how the virtual shell looks:
You can now type in commands on the virtual shell to manage your guests. Run
to get a list of available commands:
shows all running guests;
shows all guests, running and inactive:
To start a stopped guest, run:
To stop a guest, run
To immediately stop it (i.e., pull the power plug), run
Suspend a guest:
Resume a guest:
These are the most important commands.
Type
to leave the virtual shell.
 

7 Links

• Xen: http://www.xen.org/
• CentOS: http://www.centos.org/

TERIMA KASIH ATAS KUNJUNGAN SAUDARA
Semoga artikel ini bermanfaat bagi saudara. Jika ingin mengutip, baik itu sebagian atau keseluruhan dari isi artikel ini harap menyertakan link dofollow ke https://androidblackberries.blogspot.com/2012/02/virtualization-with-xen-on-centos-62.html. Terima kasih sudah singgah membaca artikel ini.