The ntp service on my xen paravirt guests does not work, how can I fix this?

Paravirtualized guests within Xen are currently configured to sync their clocks to the dom0 host. This can be problematic in situations where guest clocks need to be in sync with another time source. To change this behavior, the following command must be run:

# echo 1 > /proc/sys/xen/independent_wallclock

In order to make the change survive reboots, add the fo...