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Forcing an NTP Update

UPDATE: Dan Horrigan pointed out a much better solution to this problem on Twitter, one that has nothing to do with NTP at all. He adds a VirtualBox config option in his Vagrantfiles to update the virtual machine’s time from the host every 10 seconds. Nice!

UPDATE 2: Oops. I didn’t explain that correctly. Here’s Dan to set the matter straight:

ORIGINAL POST: I frequently find myself needing to update the time on my Vagrant boxes. This is especially true when I’m testing Query Auth between two different Vagrant boxes (mimicking a client/server relationship) as Query Auth will fail a request with a timestamp that varies too greatly from the server’s timestamp (+-15 seconds by default). Even though I run NTP on all my virtual servers, time drift is a frequent problem. Furthermore, when the drift is too great (can’t find a reference to how large the drift needs to be), NTP won’t correct it all at once.

A quick Google search later and, once again, it was Stack Overflow the rescue, courtesy of Martin Schröder’s answer to the question “How to force a clock update using ntp?”

One quick bash script later and excessive clock drift is now a trivial issue.

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#!/bin/bash
# Forces an ntp update
#
# Based on SO user Martin Schröder's answer to "How to force a clock update
# using ntp?": http://askubuntu.com/a/256004/41943

# Fail fast (set -e will bail at first error)
set -e

if [ "$EUID" -ne 0 ]; then
    echo "ERROR: '$0' must be as root."
    exit 1
fi

service ntp stop

echo "Running 'ntpd -gq'"
ntpd -gq

service ntp start

Postscript

If you’re unfamiliar with the particulars of creating bash scripts, here are the steps you can take to create your own version of the above script. You may need to preface the commands using sudo.

  • Copy and paste the above script into a text file (I’ve named mine force-ntp-update).
  • On the command line, call chmod a+x /path/to/force-ntp-update to allow all users to execute the command.
    • If you’re the only user who should be able to execute the command, change the above to chmod u+x /path/to/force-ntp-update.
  • Move the script somewhere in your path: mv /path/to/force-ntp-update /usr/local/bin.
  • Done!

Now anytime you need to force an update, simply call sudo force-ntp-update.

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