How the BeagleBone Black (Angstrom powered) synchronize his clock ?


I’m trying to understand how the BeagleBone Black synchronize his clock.

I have read the Derek Molloy blog ( but I want to understand the solution provided by the Angstrom distribution.

My BeagleBone clock is correctly set up when I start it with the Wifi USB key. It’s set up without any specific configuration. For example I don’t change the /etc/default/ntpdate file so the NTPSERVERS is still empty.
My interpretation of the /usr/bin/ntpdate-sync script is that it exit without calling nptdate if the NTPSERVERS is empty:

if [ “$NTPSERVERS” = “” ] ; then
if [ “$METHOD” = “” -a “$1” != “silent” ] ; then
echo “Please set NTPSERVERS in /etc/default/ntpdate”
exit 1
exit 0

Does it mean the BeagleBone clock is another way ? or does I’m wrong ?

from what I was finding it looks like the ntp-sync is used in the from crontab. What do you get if you crontab -l ? I found reference to where that is either ntp-sync or just set to just like you would do it manually. M
y issue with the crontab way was if it ran before network was up it would be 30 mins before it set the date/time.

Hmm… interesting. I should try to look at the scripts and decipher it sometime.

I didn’t use Derek Molloy’s techniques, but I’ve been using the one liner connman

Which works wheneven connman detects a network connection (basically it is effectively run on an ifup on an interface). This seems to work reliably on Angstrom builds.

Paul Tan.

I have found 3 access to ntpdate-sync:

  • /lib/systemd/system/ntpdate.service
  • crontab -l
  • /etc/network/if-up.d

I have put some log on the ntpdate-sync script, /etc/network/if-up.d don’t seem to be called.
In any case $NTPSERVERS is not set so my BeagleBone should not set his clock but IT DOES !!

Does some other users could confirm that her BB doesn’t set the clock if they don’t set the $NTPSERVERS ?

After some search, I fond that some server could send ntp by broadcast. This could be the case of my 3 play box.
I have installed wireshark but it doesn’t see the ntp frame, even when I use the ntpdate -b -s -u
Event in wifi nor Ethernet.

How know if there some logs about the reception of ntp broadcast frame ?

Your Beaglebone may have ntpd (ntp daemon) running with the servers defined in /etc/ntp.conf.