sudo vi /etc/ntp.conf
# 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.
#pool 0.ubuntu.pool.ntp.org iburst
#pool 1.ubuntu.pool.ntp.org iburst
#pool 2.ubuntu.pool.ntp.org iburst
#pool 3.ubuntu.pool.ntp.org iburst
# Use Ubuntu's ntp server as a fallback.
#pool ntp.ubuntu.com
pool ntp.nict.jp iburst
# Clients from this (example!) subnet have unlimited access, but only if
# cryptographically authenticated.
restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap