5.4 Creating Virtual Machines (domU)

(In this chapter I'm assuming that you've compiled a domU kernel to use with the virtual machines (/boot/vmlinuz-2.6.18-xenU). If you haven't, please replace all references to /boot/vmlinuz-2.6.18-xenU with /boot/vmlinuz-2.6.18-xen!)

We will use xen-tools to create virtual machines. xen-tools make it very easy to create virtual machines - please read this tutorial to learn more: http://www.howtoforge.com/xen_tools_xen_shell_argo. xen-tools are available as a Debian Etch package, so we install that one right now:

apt-get install xen-tools

Next we edit /etc/xen-tools/xen-tools.conf. This file contains the default values that are used by the xen-create-image script unless you specify other values on the command line. I changed the following values and left the rest untouched:

vi /etc/xen-tools/xen-tools.conf

[...]
gateway   = 192.168.0.1
netmask   = 255.255.255.0

passwd = 1

kernel = /boot/vmlinuz-2.6.18-xenU
#initrd = /boot/initrd.img-2.6.16-2-xen-686

mirror = http://ftp2.de.debian.org/debian/
[...]

Please make sure that you comment out the initrd line! At least on my installations I've never needed a ramdisk for virtual machines.

The passwd = 1 line makes that you can specify a root password when you create a new guest domain. In the kernel line you must specify the domU kernel that you want to use for your guest domains. In the mirror line specify a Debian mirror close to you.

Make sure you specify a gateway and netmask. If you don't, and you don't specify a gateway and netmask on the command line when using xen-create-image, your guest domains won't have networking even if you specified an IP address!

Now let's create our first guest domain, xen1.example.com, with the IP address 192.168.0.101:

xen-create-image --hostname=xen1.example.com --size=2Gb --swap=256Mb --ide \
--ip=192.168.0.101 --netmask=255.255.255.0 --gateway=192.168.0.1 --force \
--dir=/vserver --memory=32Mb --arch=i386 --kernel=/boot/vmlinuz-2.6.18-xenU \
--debootstrap --dist=etch --mirror=http://ftp2.de.debian.org/debian/ --passwd

A lot of switches are unnecessary here because we specified the same details in /etc/xen-tools/xen-tools.conf but it shows that you can specify the desired settings either on the command line or in /etc/xen-tools/xen-tools.conf. Please make sure that you specify --ide, otherwise your virtual machine might not boot!

(To learn more about the available options, take a look at the xen-create-image man page:

man xen-create-image

)

The xen-create-image command will now create the xen1.example.com virtual machine for us. This can take a few minutes. The output should be similar to this one:

server1:/usr/src/xen-3.1.0-src# xen-create-image --hostname=xen1.example.com --size=2Gb --swap=256Mb --ide \
>   --ip=192.168.0.101 --netmask=255.255.255.0  --gateway=192.168.0.1 --force \
>   --dir=/vserver --memory=32Mb --arch=i386 --kernel=/boot/vmlinuz-2.6.18-xenU \
>   --debootstrap --dist=etch --mirror=http://ftp2.de.debian.org/debian/ --passwd

General Infomation
--------------------
Hostname       :  xen1.example.com
Distribution   :  etch
Fileystem Type :  ext3

Size Information
----------------
Image size     :  2Gb
Swap size      :  256Mb
Image type     :  sparse
Memory size    :  32Mb
Kernel path    :  /boot/vmlinuz-2.6.18-xenU

Networking Information
----------------------
IP Address 1   : 192.168.0.101
Netmask        : 255.255.255.0
Gateway        : 192.168.0.1

WARNING
-------
Loopback module not loaded and you're using loopback images
Run the following to load the module:

modprobe loop loop_max=255


Creating swap image: /vserver/domains/xen1.example.com/swap.img
Done

Creating disk image: /vserver/domains/xen1.example.com/disk.img
Done

Creating ext3 filesystem on /vserver/domains/xen1.example.com/disk.img
Done

Installing your system with debootstrap mirror http://ftp2.de.debian.org/debian/
Done

Running hooks
Done

No role script specified.  Skipping

Creating Xen configuration file
Done
Setting up root password
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
All done


Logfile produced at:
         /var/log/xen-tools/xen1.example.com.log
server1:/usr/src/xen-3.1.0-src#

(You can ignore this warning:

WARNING
-------
Loopback module not loaded and you're using loopback images
Run the following to load the module:

modprobe loop loop_max=255

The virtual machine will work nevertheless.)

There should now be a xen1.example.com configuration file - /etc/xen/xen1.example.com.cfg. Take a look at it to become familiar with virtual machines configuration files:

cat /etc/xen/xen1.example.com.cfg

#
#  Configuration file for the Xen instance xen1.example.com, created on
# Tue May 29 01:21:54 2007.
#


#
#  Kernel + memory size
#
kernel  = '/boot/vmlinuz-2.6.18-xenU'

memory  = '32'


#
#  Disk device(s).
#
root    = '/dev/hda1 ro'

disk    = [ 'file:/vserver/domains/xen1.example.com/disk.img,hda1,w', 'file:/vserver/domains/xen1.example.com/swap.img,hda2,w' ]

#
#  Hostname
#
name    = 'xen1.example.com'


#
#  Networking
#
vif  = [ 'ip=192.168.0.101' ]

#
#  Behaviour
#
on_poweroff = 'destroy'
on_reboot   = 'restart'
on_crash    = 'restart'

To start the virtual machine, run

xm create /etc/xen/xen1.example.com.cfg

Run

xm console xen1.example.com

to log in on that virtual machine (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 (192.168.0.101).

To get a list of running virtual machines, type

xm list

The output should look like this:

server1:~# xm list
Name                                      ID   Mem VCPUs      State   Time(s)
Domain-0                                   0   301     1     r-----   1191.0
xen1.example.com                           1    32     1     -b----     50.6
server1:~#

To shut down xen1.example.com, do this:

xm shutdown xen1.example.com

If you want vm01 to start automatically at the next boot of the system, then do this:

ln -s /etc/xen/xen1.example.com.cfg /etc/xen/auto

Here are the most important Xen commands:

xm create -c /path/to/config - Start a virtual machine.
xm shutdown <name> - Stop a virtual machine.
xm destroy <name> - Stop a virtual machine immediately without shutting it down. It's as if you switch off the power button.
xm list - List all running systems.
xm console <name> - Log in on a virtual machine.
xm help - List of all commands.

Let's create a second vm, xen2.example.com with the IP address 192.168.0.102:

xen-create-image --hostname=xen2.example.com --size=2Gb --swap=256Mb --ide \
--ip=192.168.0.102 --netmask=255.255.255.0 --gateway=192.168.0.1 --force \
--dir=/vserver --memory=32Mb --arch=i386 --kernel=/boot/vmlinuz-2.6.18-xenU \
--debootstrap --dist=etch --mirror=http://ftp2.de.debian.org/debian/ --passwd

Afterwards, you can start xen2.example.com like this:

xm create /etc/xen/xen2.example.com.cfg

and shut it down like this:

xm shutdown xen2.example.com

A list of all virtual machines that were created with the xen-create-image command is available under

xen-list-images

server1:~# xen-list-images
Name: xen1.example.com
Memory: 32
IP: 192.168.0.101

Name: xen2.example.com
Memory: 32
IP: 192.168.0.102
server1:~#

To learn more about what you can do with xen-tools, take a look at this tutorial: http://www.howtoforge.com/xen_tools_xen_shell_argo

You can check which kernel you are using by running

uname -a

You can do this on both dom0 and domU. For example, on my xen1.example.com virtual machine for which I have compiled a special domU kernel, the output looks like this:

xen1:~# uname -a
Linux xen1.example.com 2.6.18-xenU #2 SMP Tue May 29 00:53:13 CEST 2007 i686 GNU/Linux
xen1:~#