Ubuntu DomainU Fails to boot with "Error: Device 0 (vif) could not be connected. Could not find bridge, and none was specified".

After installing the xen-server packages on an Ubuntu system and creating a Xen domainU system the guest fails to boot with the following output:

"Error: Device 0 (vif) could not be connected. Could not find bridge, and none was specified".

This problem relates to the networking configuration of the Xen domain0 on the host system. By default, the Ubuntu implementation of Xen is installed with networking support disabled. If the domainU configuration file contains a vif directive, therefore, domain0 will be unable to find a network bridge for the domainU guest.

In order to rectify this problem, simply edit Xend configuration file. The default location for this file is:

/etc/xen/xend-config.sxp

Once the file is loaded into a suitable editor, simply comment out the following line:

(network-script network-dummy)

so that it appears as follows:

#(network-script network-dummy)

Once this line has been commented out, add a new line beneath it enabling the network bridge so that that the two lines appear as follows:

#(network-script network-dummy)
(network-script network-bridge)

Having made these changes save the Xend configuration file and then restart the xend daemon:

sudo /init.d/xend restart

If restarting the Xen daemon fails to resolve the problem it may be necessary to reboot the host system for the change to take effect.