3. Virtualization

3. Virtualization
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Abstract

This chapter discusses the concepts and procedures to implement virtual machines on your Mandriva Enterprise Server 5 using Xen, KVM or graphical tool Virt-manager. This will allow you to run multiple OSes within your Mandriva Linux server.

3.1. Xen

3.1.1. General Concepts and Main Web References

Xen is a virtual machine monitor for x86 hardware (it runs on i686 and x86-64 CPU classes). It supports running multiple guest operating systems on a single machine. Guest OSes (also called “domains”) require a modified kernel which supports Xen hypercalls to replace physical hardware access. At boot, the Xen kernel is loaded (via GRUB) along with the guest kernel for the first domain (called “domain0”). domain0 has privileges to access the physical hardware (PCI and ISA devices), to manage other domains, as well as to provide virtual devices (disks and network) for other domains.

Here are the main Web references which discuss the configuration of Xen :

3.1.2. Installing and Configuring Domains

3.1.2.1. Before Starting

We installed Mandriva Mandriva Enterprise Server 5 on a 12 GB disk. During the installation, we created a partition of 5 GB. Its file system is mounted on / for the domain0 installation. Additionally, we created a swap partition of 256 MB on /dev/sda5.

We now have 7 GB left. We created two partitions of 3.2 GB, that are not yet mounted, for two guest domains os installations, and two swap spaces of 256 MB each.

Here is the partition table :

root domain0 -> sda1
swap domain0 -> sda5
	
root guest1 -> sda6
swap guest1 -> sda7
	
root guest2 -> sda8
swap guest2 -> sda9

3.1.2.2. Installing RPMS

Mandriva Enterprise Server 5 provides the required patches in the kernel so that the Xen functionality is implemented. You will also need both specific kernels and tools to manage virtualization.

# urpmi kernel-xen xen

3.1.2.3. Configuring domain0

Installation of xen package provides a bootloader configuration and an initrd creation. What follows is a reminder to configure domain0. You have to set up the automatic start of xen services at boot time..

Configuring GRUB

An entry has been added to the GRUB configuration file (/boot/grub/menu.lst) so that Xen/Xenolinux can boot. The entry should look like :
```
title XEN 3 / Mandriva Enterprise Server 5
kernel (hd0,0)/boot/xen.gz dom0_mem=131072
module (hd0,0)/boot/vmlinuz-2.6.18.8-xen-3.3.0-7mdv root=/dev/sda1 ro
module (hd0,0)/boot/initrd-2.6.18-8-xen-3.3.0-7mdv.img
     
```
Review of main parameters :

kernel

Tells GRUB where Xen itself is located and parameters to be taken into account by the kernel (in this case, setting domain0 size of allocation memory in kilobytes).

module

The first line tells you where to find the Xenolinux kernel that Xen should launch with parameters. These are standard Linux parameters, root device identification and initial read-only mount.

module

The second line contains the path of initrd. It must be the module and not initrd in GRUB configuration, otherwise Xen will not boot.
Creating initrd

We are now going to create initrd so that Xen guest domains will be managed at boot :
```
# mkinitrd -v -f /boot/initrd-2.6.18.8-xen-3.3.0-7mdv.img
2.6.18.8-xen-3.3.0-7mdv
```
Note

When adding the new kernel in menu.lst, it's recommended that you keep your existing entries. You could have to reboot on your old Linux kernel if you have problems.
Starting Xen services

At the end of the installation and configuration process, reboot your system and choose the Xen entry in the GRUB menu.

During your system's start-up, the first part of the output displays information for Xen itself (low level and hardware). The last part of the output displays information for Xenolinux.

To create additional domains, start the xend daemon control. You can also start the xendomains daemon, which launches additional domains at domain0's boot.
```
# chkconfig --add xend
# chkconfig --add xendomains
# service xend start
# service xendomains start
     
```

At this point, you can use the xm tool to monitor or maintain domains running on your system.

3.1.2.4. Installation of Guest Domains

The first step in creating an additional domain is to prepare a root filesystem for it to boot. Typically, this might be stored in a normal partition, an LVM partition, a disk file or on an NFS server. A simple solution to do this is to boot from a system installation disk and install the distribution onto a new partition of your hard drive.

In the following sections, we will give an other option to create an additional domain based on a copy of domain0's root partition, installed with urpmi in a physical partition or in a file.

# mkdir -p /mnt/xen

Partition Copy. The main advantage of this method is that the installation disk is not needed. We copy the root partition of domain0 on another partition of the hard drive to obtain a second filesystem that will be used by the guest domain.

# mount /dev/sda6 /mnt/xen
# rsync -avDx / /mnt/xen
# cp -ar /dev/* /mnt/xen/dev/
# umount /mnt/xen

	Warning
	The rsync command will synchronize only root filesystems, it doesn't follow a mount link to other filesystems.

If your /usr and /var are separate, redo it for each mount point, except for the network and special entries.

If you have different partition schemes between domain0 and additional domains, don't forget to adapt the /etc/fstab file to the guest domain's filesystem.

Install Mandriva Enterprise Server 5 with urpmi. With urpmi, you can get a clean installation of a new Mandriva Enterprise Server 5.

You have to configure guest domain /etc/fstab file. For example, the partition /dev/sda6 becoming /dev/sda1 :

/dev/sda1 / ext3 relatime,user_xattr,acl 1 1
/dev/sda5 swap swap defaults 0 0
none /proc proc defaults 0 0

First, mount your clean partition :
```
# mount /dev/sda6 /mnt/xen
```
Set up your urpmi media :
```
# urpmi.addmedia --distrib --urpmi-root /mnt/xen url
  
```
You must configure url to point to the directory containing the installation media.
Install the guest domain Mandriva Enterprise Server 5 system base and use urpmi to install new packages.
```
# urpmi --urpmi-root /mnt/xen basesystem urpmi
     
```
At the prompt, you will be asked many questions. Answer them as you would proceed for a classical installation (choosekernel-xen).
The following steps configure the new features :

Copy configuration files for domain0.
```
# cp /etc/resolv.conf /mnt/xen/etc
# cp /etc/fstab /mnt/xen/etc
```

Copy the networking configuration from domain0.

# cp /etc/sysconfig/network-scripts/ifcfg-eth0 \
/mnt/xen/etc/sysconfig/network-scripts

Install dhcp client if necessary.

# urpmi --urpmi-root /mnt/xen dhcp-client

Enter chroot for final configuration.
```
# chroot /mnt/xen
```

Create empty necessary configuration files.

# touch /etc/mtab /etc/urpmi/urpmi.cfg /var/lib/urpmi/MD5SUM

Create shadow from passwd.
```
# pwconv
```
Turn on network by creating the /etc/sysconfig/network file with the following content :
```
NETWORKING=yes
```
Set root password.
```
# passwd root
```
Exit chroot's shell.
```
# exit
```
Umount guest partition.
```
# umount /mnt/xen
```

Installing Mandriva Enterprise Server 5 in a File. This way of working has the advantage of not modifying the partition structure of your hard drive. We will explain how to create and mount a disk image. Then you can choose one of two methods below (urpmi or making a copy of the root partition).

First, create an image file for your Mandriva Enterprise Server 5 guest domain. This command creates a disk image of 1GB, filled with zeroes, in a file named mandriva.img located in the current directory.
```
# dd if=/dev/zero of=mandriva.img bs=1M count=1 seek=1024
```
Create a filesystem in the image file. The
```
-j
```
option specifies an ext3 filesystem.
```
# mke2fs -F -j mandriva.img
```
Finally, you can mount your image file on a mount point.
```
# mount -o loop mandriva.img /mnt/xen
```

You can now use this mount point like a physical partition's mount point and install Mandriva Enterprise Server 5.

In the guest domain's configuration file, the disk options should be modified so that phy:sdaX is replaced by file:path/of/file. Otherwise, other options are similar.

3.1.2.5. Configuration of Additional Domains

Before you can launch an additional domain, you should create a configuration file for guest domains. The following section describes these steps. This file is not essential but will help you to get guest domains to boot without any problems.

Create a Guest Domain Configuration File. The following configuration file (call it “mandriva”) should be located in the /etc/xen directory in domain0 if you want to launch it manually, or in the /etc/xen/auto directory if you want to launch it automatically by xendomains at boot.

kernel = "/boot/vmlinuz-2.6.18.8-xen-3.3.0-7mdv" 
ramdisk = "/boot/initrd-xen-2.6.18.8-xen-3.3.0-7mdv.img"
memory = 128 
name = "Mandriva"
dhcp = "dhcp" 
disk = [ 'phy:sda6,sda1,w', 'phy:sda7,sda5,w' ] 
root = "/dev/sda1 ro" 
extra = "xencons=tty" 
hostname = "mandriva2009"
vif = [ '' ]

This file shows the most common options used for a domain definition. Here's a short description of each option :

kernel: Establishes the link to the kernel compiled for Xen.
memory: Set it to the size of the guest domain's memory in megabytes.
name: Name of the additional domain.
dhcp: Uncomment the dhcp variable so that the domain will receive its IP address from a DHCP server.
disk: List of block devices exported to the guest domain. In this example, the sda6 physical partition is named sda1 in the additional domain and will be the root partition with the following root option. The sda7 partition is a swap. If your disk is an image file, you should replace phy:sdaX by file:path/of/file. The w option explains the read-write rights to access this partition. You could also use the r option to set the partition as read-only.
root: Specify the root device parameter on the kernel command line. We must take the partition scheme of the disk option.
extra: Extra string to append to the kernel command line.
hostname: Guest domain hostname.
vif: The configuration of the network interface of the guest.

All the configuration modifications detailed in the next sections must be made in the guest domain, not in domain0 as before. There are two possibilities :

Launch the additional domain with the xm create -c /etc/xen/auto/mandriva command. Then modify the guest domain directly in it.
Type a chroot command such as :
```
chroot /mnt/xen
```
To exit the chroot shell, type exit and don't forget to unmount the /mnt/xen filesystem (umount /mnt/xen).

Réseautique

Let's use the last method.

Modifying /etc/inittab. If you don't want to receive annoying messages such as :

INIT: Id "2" respawning too fast: disabled for 5 minutes 
INIT: Id "3" respawning too fast: disabled for 5 minutes 
INIT: Id "4" respawning too fast: disabled for 5 minutes 
INIT: Id "5" respawning too fast: disabled for 5 minutes 
INIT: Id "6" respawning too fast: disabled for 5 minutes

In your guest console, you should comment unused terminals in the /etc/inittab file like this :

1:2345:respawn:/sbin/mingetty tty1
#2:2345:respawn:/sbin/mingetty tty2
#3:2345:respawn:/sbin/mingetty tty3
#4:2345:respawn:/sbin/mingetty tty4
#5:2345:respawn:/sbin/mingetty tty5
#6:2345:respawn:/sbin/mingetty tty6

xend and xendomains Services. If you installed your system with a domain root filesystem copy, then xend and xendomains services are probably configured to start at boot time. It's useless for an additional domain. We will disable it as follows :
```
# /etc/init.d/xend stop
# /etc/init.d/xendomains stop
# chkconfig xend off
# chkconfig xendomains off
```
Keytable Service. Here is a little hint to avoid failure messages when keymap is loading at guest domain boot. You should disable the keytable service with :
```
# chkconfig keytable off
# /etc/init.d/keytable stop
```
But it's not enough because this service is called directly in the /etc/rc.d/rc.sysinit file. We will comment out the following three lines (905,906,907) :
```
#if [ -x /etc/init.d/keytable -a -d /usr/lib/kbd/keymaps ]; then
#    /etc/init.d/keytable start 
#fi
```
Notice that the keytable and numlock (see following section) services are not necessary in additional domains because domain0 has already initialized numlock and all domains use the same keyboard.
Numlock Service. Finally, in the configuration file of the guest domain, we get this message when the numlock service is started or when we log in :
```
KDGETLED: Argument invalide Error reading current led setting. 
Maybe stdin is not a VT?
		
```
To avoid this problem, disable the following :
```
# /etc/init.d/numlock stop 
# chkconfig numlock off
```
At this step, we have a Xen system which contains the domain0 and one or more clean additional domains ready for execution.

3.1.3. Managing Guest Domains

3.1.3.1. Configuration réseau

This section explains Xen network basics and configuration.

Networking

The network scheme is very simple. domain0 has real Ethernet interface control. Each guest domain has a virtual network interface. In additional domains, this interface is a normal Ethernet interface but it's named vifX.Y with “X” is the number interface (0 for eth0) and Y is the number of its own instance domain. All vif and eth interfaces are connected on the peth0 bridge for network access.

See XenNetworking for detailed information on networking with Xen.

You will find a documentation and explanations on les interfaces Ethernet interfaces, MAC addresses, bridging, routing, interface names, VLANs, etc.

3.1.3.2. The xm Tool

The xm tool provides many options for managing domains. Here's a quick review :

Start guest domains : Before you start a domain, you should create a config file for it.

To start an additional domain :
```
# xm create -c /etc/xen/auto/mandriva
```
The create command starts a new domain instance. The -c option configures the console domain so that it should output immediately and mandriva is the name of the additional domain you start. You should now see a list of running domains :
```
# xm list
```
You will find more details about syntax commands and options thorough the xm help command.
Using the Xen console : if you don't specify the -c option at start time, you can still use the console.
```
# xm console Mandriva
```
Mandriva is the name of the guest domain target. You can replace it with the guest ID displayed in the xm list.

To quit a guest console, just type Ctrl+] (Ctrl+$ dans une console virtuelle locale ou tty).
Guest domain backup and restore: Administrators of a Xen system can suspend a virtual machine in its current state into a disk file in domain0, allowing it to resume at a later time.

For example, you can suspend a domain called mandriva to disk :
```
# xm save Mandriva mandriva.chk
```
This stops the domain named mandriva and saves its current state into a file called mandriva.chk.

To resume execution of this domain, use the xm restore command :
```
# xm restore mandriva.chk
```
This restores the state of the domain and resumes its execution. The domain will restart in the same state and the console may be reconnected using the xm console Mandriva command.

3.1.4. Troubleshooting

If you get the following error :
```
Error: Error creating domain (12, 'Cannot allocate memory')
```
add the dom0_mem option on the Xen command line in the grub.conf entry :

If you get the following error :

Error: Error creating domain: Kernel image does not exist :
/boot/vmlinuz-2.6.18.8-xen-3.3.0-7mdv

please install the kernel-xen package.

3.2. KVM

3.2.1. Main concepts and web references

KVM (Kernel-based Virtual Machine) is a virtualization solution for x86 architectures based on Intel VT (vmx) and AMD-V (svm) technologies. To determine if such an extension is supported by your hardware, run the following command:

# grep ‘(vmx|svm)’ /proc/cpuinfo

	Note
	If you know that your processor includes a virtualisation extension even if it is not displayed, please check if your BIOS is well configured. If the option is not enable, do it. For the modification to be taken into account, a hardware reboot is not enough, you have to completely shut down the server.

With KVM, you can deploy Linux or Windows^® virtual machines.

The KVM website is located here: linux-kvm.org

3.2.2. Installation

You will need both qemu-img and kvm packages

# urpmi qemu-img kvm

To use KVM, the kernel module must be loaded. You can verify it thanks to the following command:

# lsmod |grep kvm

In case you have the AMD-V technology and if this module is not loaded, load it with:
```
# modprobe kvm-amd
```
In case you have the Intel VT technology and if this module is not loaded, load it with:
```
# modprobe kvm-intel
```

The user which will be used to create your virtual machines must belong to the kvm group (here, the user is named 'test').

#usermod -G kvm test

Check with the id command that you user belongs to the kvm group:

$id
uid=500(test) gid=500(test) groupes=422(kvm),500(test)

3.2.3. Installing Virtual Machines

Be aware you'll need enough free space on your hard disk to host your virtual machines. You can create a dedicated partition for that use.

First, you have to create an image of the guest virtual machine. The following command create an image of 3GiB maximum size.

$ qemu-img create mes5dvd 3G
Formatting 'mes5dvd', fmt=raw, size=3145728 kB

Different file formats exist. Please read the qemu-img man page to know the different possible file formats.

We are going to install Mandriva Enterprise Server 5 from the installation DVD media into the mes5dvd image we just have created.

kvm -k fr -m 512 -cdrom /dev/cdrom -drive file=mes5dvd

the options stands for:

-k en-us : english keyboard.
-m 512 : the virtual machine will have 512 MiB of RAM memory.
-cdrom /dev/cdrom : the virtual machine of the cdrom device will be /dev/cdrom, i.e. the physical machine cdrom device.
-drive file=mes5dvd : the harddisk of the machine will be the mes5dvd file.

The CD or DVD installation media present into you CDROM/DVDROM device is bootable. Once the command is launched, a window appears and the virtual machine installation process begins. Install Mandriva Enterprise Server 5 completely.

To launch your virtual machine:

kvm -k en-us -m 512 -cdrom /dev/cdrom -drive file=mes5dvd,boot=on

Many options can be passed to KVM (please read man kvm).

With the method described upwards, your virtual machine will have network (same network access than the host machine). KVM deals with the network configuration on its own. If you want to intall several virtual machines, you will have to configure a bridge connection and configure your virtual machines as a NAT. To know how to configure a bridge and how to use it with KVM, you can read the documentation available at linux-kvm.org

3.3. Virt-manager

Abstract

The "Virtual Machine Manager" application (Virt-manager) is a desktop user interface to configure and manage virtual machines, virtual networks and storage. It is possible to manage Xen, KVM or QEMU guests.

3.3.1. How to start Virt-manager

Virt-manager uses libvirtd so it is necessary to start it:

#/etc/init.d/libvirtd start

To add libvirtd on default start:

#chkconfig libvirtd on

If you use Xen, start xend daemon. If you use KVM, then load the kvm module.

So, now that you are ready to start Virt-manager, choose Applications > Tools > Emulators > Virtual Machine Manager:

Figure 5.12. Launch Virt-manager

or use the command line :

#virt-manager

3.3.2. Virt-manager use

3.3.2.1. Guest creation

When Virt-manager is connected to your virtualisation system (Xen or KVM or QEMU), you can add a new guest by clicking on New.

Figure 5.13. Guest's creation

3.3.2.2. Virtual networks and storage configuration

To configure your virtual networks and storage, click right on Your domain > Details

Figure 5.14. Virtual networks configuration

You can find more informations on official Virt-manager website.

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	Note
	When adding the new kernel in menu.lst, it's recommended that you keep your existing entries. You could have to reboot on your old Linux kernel if you have problems.