Comment 1 for bug 1706818

Thank you for taking the time to report this bug and helping to make Ubuntu better.

I've confirmed that the issue is as you describe in Xenial. Trusty pre-dates the change to locking in ntp.if-up, so is consistent. Zesty is also consistent in using flock in both places, as is Artful. So this bug affects only Xenial.

In order to understand the importance of this bug, please could you explain why you're using both ntp and ntpdate? ntpdate isn't installed by default on Xenial, and shouldn't be required in the normal case because ntp defaults to "-g". So you could work around this bug by just removing the ntpdate package. Is there a particular reason that this won't work in your case?