3 Creating Virtual Machines (domU)

Now let's create our first guest domain, xen1.example.com, running Hardy Heron (hardy) 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=/home/xen --memory=64Mb --arch=i386 --kernel=/boot/vmlinuz-2.6.24-16-xen \
--initrd=/boot/initrd.img-2.6.24-16-xen --install-method=debootstrap --dist=hardy \
--mirror=http://archive.ubuntu.com/ubuntu/ --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:

root@server1:~# 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=/home/xen --memory=64Mb --arch=i386 --kernel=/boot/vmlinuz-2.6.24-16-xen \
> --initrd=/boot/initrd.img-2.6.24-16-xen --install-method=debootstrap --dist=hardy \
> --mirror=http://archive.ubuntu.com/ubuntu/ --passwd

General Information
--------------------
Hostname       :  xen1.example.com
Distribution   :  hardy
Partitions     :  swap            256Mb (swap)
                  /               2Gb   (ext3)
Image type     :  sparse
Memory size    :  64Mb
Kernel path    :  /boot/vmlinuz-2.6.24-16-xen
Initrd path    :  /boot/initrd.img-2.6.24-16-xen

Networking Information
----------------------
IP Address 1   : 192.168.0.101 [MAC: 00:16:3E:62:DA:BB]
Netmask        : 255.255.255.0
Broadcast      : 192.168.0.255
Gateway        : 192.168.0.1


Creating partition image: /home/xen/domains/xen1.example.com/swap.img
Done

Creating swap on /home/xen/domains/xen1.example.com/swap.img
Done

Creating partition image: /home/xen/domains/xen1.example.com/disk.img
Done

Creating ext3 filesystem on /home/xen/domains/xen1.example.com/disk.img
Done
Installation method: debootstrap
Done

Running hooks
Done

No role scripts were 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
root@server1:~#

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 machine configuration files:

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

# Configuration file for the Xen instance xen1.example.com, created
# by xen-tools 3.8 on Tue May  6 16:01:38 2008.
#
#
#  Kernel + memory size
#
kernel      = '/boot/vmlinuz-2.6.24-16-xen'
ramdisk     = '/boot/initrd.img-2.6.24-16-xen'
memory      = '64'
#
#  Disk device(s).
#
root        = '/dev/hda2 ro'
disk        = [
                  'file:/home/xen/domains/xen1.example.com/swap.img,hda1,w',
                  'file:/home/xen/domains/xen1.example.com/disk.img,hda2,w',
              ]

#
#  Hostname
#
name        = 'xen1.example.com'
#
#  Networking
#
vif         = [ 'ip=192.168.0.101,mac=00:16:3E:62:DA:BB' ]
#
#  Behaviour
#
on_poweroff = 'destroy'
on_reboot   = 'restart'
on_crash    = 'restart'
extra = '2 console=xvc0'

The file: parameter is now deprecated in Xen 3.2, therefore we must edit /etc/xen/xen1.example.com.cfg now and replace file: with tap:aio: (otherwise you'll get an error similar to this one:

Error: Device 769 (vbd) could not be connected. losetup /dev/loop0 /home/xen/domains/xen1.example.com/swap.img failed

when you try to start a vm - see http://ubuntuforums.org/showthread.php?t=770902 as well):

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

[...]
disk        = [
                  'tap:aio:/home/xen/domains/xen1.example.com/swap.img,hda1,w',
                  'tap:aio:/home/xen/domains/xen1.example.com/disk.img,hda2,w',
              ]
[...]

(Please note: if you have a dual-core CPU and want the virtual machine to use both CPU cores, please add the line vcpus = '2' to the configuration file, like this:

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

# Configuration file for the Xen instance xen1.example.com, created
# by xen-tools 3.8 on Mon May  5 16:49:32 2008.
#
#
#  Kernel + memory size
#
kernel      = '/boot/vmlinuz-2.6.24-16-xen'
ramdisk     = '/boot/initrd.img-2.6.24-16-xen'
memory      = '64'
vcpus       = '2'
[...]

Afterwards, in the virtual machine, you can run the command

cat /proc/cpuinfo

to check that both CPU cores are being used by the virtual machine. The output could look like this if your vm is using both cores:

xen1:~# cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 75
model name      : AMD Athlon(tm) 64 X2 Dual Core Processor 4200+
stepping        : 2
cpu MHz         : 2210.054
cache size      : 512 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu tsc msr pae mce cx8 apic mca cmov pat pse36 clflush mmx fxsr
 sse sse2 ht syscall nx mmxext fxsr_opt lm 3dnowext 3dnow pni cx16 lahf_lm cmp_legacy svm
 cr8legacy ts fid vid ttp tm stc
bogomips        : 5526.81

processor       : 1
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 75
model name      : AMD Athlon(tm) 64 X2 Dual Core Processor 4200+
stepping        : 2
cpu MHz         : 2210.054
cache size      : 512 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu tsc msr pae mce cx8 apic mca cmov pat pse36 clflush mmx fxsr
 sse sse2 ht syscall nx mmxext fxsr_opt lm 3dnowext 3dnow up pni cx16 lahf_lm cmp_legacy svm
 cr8legacy ts fid vid ttp tm stc
bogomips        : 5526.81

xen1:~#

)

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).

In the virtual machine (when you use it for the first time), run

mv /lib/tls /lib/tls.disabled

Now back to the host system (dom0). To get a list of running virtual machines, type

xm list

The output should look like this:

root@server1:~# xm list
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0   569     1     r-----    103.6
xen1.example.com                             1    64     1     -b----     60.8
root@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=/home/xen --memory=64Mb --arch=i386 --kernel=/boot/vmlinuz-2.6.24-16-xen \
--initrd=/boot/initrd.img-2.6.24-16-xen --install-method=debootstrap --dist=hardy \
--mirror=http://archive.ubuntu.com/ubuntu/ --passwd

Then open the configuration file of the vm, /etc/xen/xen2.example.com.cfg, and replace file: with tap:aio: again:

vi /etc/xen/xen2.example.com.cfg

[...]
disk        = [
                  'tap:aio:/home/xen/domains/xen2.example.com/swap.img,hda1,w',
                  'tap:aio:/home/xen/domains/xen2.example.com/disk.img,hda2,w',
              ]
[...]

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

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

(Don't forget to run

xm console xen2.example.com

and

mv /lib/tls /lib/tls.disabled

when you're in the vm for the first time!)

... 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

root@server1:~# xen-list-images
Name: xen1.example.com
Memory: 64
IP: 192.168.0.101

Name: xen2.example.com
Memory: 64
IP: 192.168.0.102
root@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

4 Links

• Xen: http://www.xensource.com/xen/
• xen-tools: http://xen-tools.org/software/xen-tools
• Ubuntu: http://www.ubuntu.com/