Sync ubuntu server time

$ sudo ntpdate-debian

Or do it all the time:

$ sudo apt-get install ntp

NTP security

Protect yourself against NTP server attacks by adding disable monitor to your /etc/ntp.conf file.
Disabling monitoring will prevent unwanted remote queries that use commands from older versions of NTP, such as monlist.

Also see:

https://support.rackspace.com/how-to/using-ntp-to-sync-time/