Virtualization With Xen 3.3.1 On Debian Etch - Page 3
5 Creating LVM-Based Virtual Machines
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 Debian Etch host with the LVM volume group /dev/vg0 that has about 50GB of space. /dev/vg0 contains two logical volumes, /dev/vg0/root and /dev/vg0/swap_1 that consume about 12GB of space - the rest is not allocated and can be used to create logical volumes for our virtual machines:
Now 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:
Make sure that you uncomment the lvm line and fill in the name of your volume group (vg0 in my case). At the same time make sure that the dir line is commented out!
dist specifies the distribution to be installed in the virtual machines (Debian Etch) (there's a comment in the file that explains what distributions are currently supported).
The passwd = 1 line makes that you can specify a root password when you create a new guest domain.
In the mirror line specify a Debian mirror close to you.
Make sure you specify a gateway, netmask, and broadcast address. 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!
It is very important that you add the line serial_device = hvc0 (or serial_device = xvc0) because otherwise your virtual machines might not boot properly!
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=4Gb --swap=256Mb --ip=192.168.0.101 --memory=128Mb --arch=i386 --role=udev
Options that you specify on the command line override the settings in /etc/xen-tools/xen-tools.conf. Options that are not specified on the command line are taken from /etc/xen-tools/xen-tools.conf. Please make sure that you add --role=udev, or your virtual machine might not boot properly!
(To learn more about the available options, take a look at the xen-create-image man page:
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:~# xen-create-image --hostname=xen1.example.com --size=4Gb --swap=256Mb --ip=192.168.0.101 --memory=128Mb --arch=i386 --role=udev
As you see from the output, xen-create-image has created a new logical volume for our VM in the vg0 volume group, /dev/vg0/xen1.example.com-disk, for the VM's root filesystem. Take a look at
and you will see that it has also created a second logical volume, /dev/vg0/xen1.example.com-swap, for the VM's swap:
There should now be a xen1.example.com configuration file - /etc/xen/xen1.example.com.cfg. Open it and add the line extra = 'xencons=hvc0 console=hvc0' (or extra = 'xencons=xvc0 console=xvc0' if you use serial_device = xvc0 in /etc/xen-tools/xen-tools.conf) at the end so that the file looks as follows:
If you don't add that line and you go to the console of the vm using the xm console command, the boot process seems to hang forever (while in fact, the vm is running perfectly fine - you can connect to it using SSH).
(If we had used disk images instead of logical volumes, the disk line would look similar to this one:
disk = [ 'file:/path/to/xen1.example.com/disk.img,xvda1,w', 'file:/path/to/xen1.example.com/swap.img,xvda2,w' ]
(Please note: if you have a dual-core or quad-core CPU and want the virtual machine to use all CPU cores, please add the line vcpus = '2' or vcpus = '4' to the configuration file.)
To start the virtual machine, run
xm create /etc/xen/xen1.example.com.cfg
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).
(If you see something like this during the boot process of the vm...
EXT3-fs: mounted filesystem with ordered data mode.
... run the following command in the vm:
mv /lib/tls /lib/tls.disabled
To get a list of running virtual machines, type
The output should look like this:
server1:~# xm list
To shut down xen1.example.com, do this:
xm shutdown xen1.example.com
If you want xen1.example.com 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.
A list of all virtual machines that were created with the xen-create-image command is available under
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