Currently XenServer does not have a template for the new Ubuntu 14.04. This will most likely be fixed in a future update, but for now it’s a really easy to add a new template. Thanks to http://virantha.com/2014/05/21/ubuntu-14-04-trusty-on-xenserver-62/ for the quick instructions.

In XenCenter, head over to the console of the server and log in.

Run the following 3 commands (I chose to name it the full name Trusty Tahir instead of just Trusty):

TEMPLATE_UUID=`xe template-list name-label="Ubuntu Lucid Lynx 10.04 (64-bit)" params=uuid --minimal`
NEW_TEMPLATE_UUID=`xe vm-clone uuid=$TEMPLATE_UUID new-name-label="Ubuntu Trusty Tahir 14.04 (64-bit)"`
xe template-param-set other-config:default_template=true other-config:debian-release=trusty uuid=$NEW_TEMPLATE_UUID

These three commands basically just copy the template from Lucid Lunx 10.04 and renames it. Simples!