Q: SES time sync error My SES setup was running fine for the last 6 months without any issues. All of a sudden it stopped working yesterday and I'm gettinng the infamous time sync error.
Naturally I assumed ntpd had stopped, but to my surprise when I checked the process tree, I noticed that it was running. 
 ~  ps auwx | grep ntpd                                 
ntp      18223  0.0  0.0  33600  2132 ?        Ss   07:05   0:00 /usr/sbin/ntpd -p /var/run/ntpd.pid -g -u 106:112
ubuntu   19127  0.0  0.0   8144   668 pts/5    S+   07:19   0:00 grep ntpd

Then I tried ntpdate which said
2 Sep 07:16:09 ntpdate[18966]: no servers can be used, exiting

I checked the /etc/ntp.conf file which had the default ubuntu servers listed by default. 
# /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help

driftfile /var/lib/ntp/ntp.drift


# Enable this if you want statistics to be logged.
#statsdir /var/log/ntpstats/

statistics loopstats peerstats clockstats
filegen loopstats file loopstats type day enable
filegen peerstats file peerstats type day enable
filegen clockstats file clockstats type day enable

# Specify one or more NTP servers.

# Use servers from the NTP Pool Project. Approved by Ubuntu Technical Board
# on 2011-02-08 (LP: #104525). See http://www.pool.ntp.org/join.html for
# more information.
server 0.ubuntu.pool.ntp.org
server 1.ubuntu.pool.ntp.org
server 2.ubuntu.pool.ntp.org
server 3.ubuntu.pool.ntp.org

# Use Ubuntu's ntp server as a fallback.
server ntp.ubuntu.com

# Access control configuration; see /usr/share/doc/ntp-doc/html/accopt.html for
# details.  The web page <http://support.ntp.org/bin/view/Support/AccessRestrictions>
# might also be helpful.
#
# Note that "restrict" applies to both servers and clients, so a configuration
# that might be intended to block requests from certain clients could also end
# up blocking replies from your own upstream servers.

# By default, exchange time with everybody, but don't allow configuration.
restrict -4 default kod notrap nomodify nopeer noquery
restrict -6 default kod notrap nomodify nopeer noquery

# Local users may interrogate the ntp server more closely.
restrict 127.0.0.1
restrict ::1

# Clients from this (example!) subnet have unlimited access, but only if
# cryptographically authenticated.
#restrict 192.168.123.0 mask 255.255.255.0 notrust


# If you want to provide time to your local subnet, change the next line.
# (Again, the address is an example only.)
#broadcast 192.168.123.255

# If you want to listen to time broadcasts on your local subnet, de-comment the
# next lines.  Please do this only if you trust everybody on the network!
#disable auth
#broadcastclient

I couldn't spot the issue here. Then I tried to check the status of NTP server and found no issues there. 
/etc/init.d/ntp status                             
 * NTP server is running

I also tried adding a NTP server manually to see if it worked, but that didn't help either
 sudo ntpdate ntp.ubuntu.com                         
 2 Sep 07:20:08 ntpdate[19203]: the NTP socket is in use, exiting

I really don't understand what the issue is  here. Why is ntpd not working when it's running in the background? 
Any help would be appreciated. Thanks. 

A: You need to stop ntpd before running ntpdate.
sudo service ntp stop
sudo ntpdate 0.ubuntu.pool.ntp.org
sudo service ntp start


A: On ubuntu you should use 
ntpd -q

instead of ntpdate if you have installed ntpd
Manpage:
-q     Exit the ntpd just after the first time the clock is set.  This behavior mimics that of the ntpdate program, which is to be retired.
       The -g and -x options can be used with this option.  Note: The kernel time discipline is disabled with this option.

