set time

date --set="23 June 1988 10:00:00"
date --set="10:00:00"

Set the Hardware Clock to the current System Time
# hwclock --systohc

Set the System Time from the Hardware Clock.
# hwclock --hctosys

update via ntp

via ntpd

sudo service ntp stop
sudo ntpd -gq
sudo service ntp start

via ntpdate

ntpdate ntp.ubuntu.com

ntp server