How to Setup NTP server and Client (CentOS/RHEL)

NTP (Network time protocol) is used to  synchronize a computer's time in a local network (usually behind firewall )with another reference time source.

Steps:
1. Install NTP package
2. configure ntp.conf
3. start ntpd daemon
4.check   with ntpq -n

check the correct

cat /etc/sysconfig/clock

rpm -qa ntp

one US and one Canada NTP Server

http://www.pool.ntp.org/zone/north-america

http://www.pool.ntp.org/zone/ca

http://support.ntp.org/bin/view/Servers/StratumOneTimeServers


vim /etc/ntp.conf
# permit the source to query or modify the service on this system.
restrict default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery

# Permit all access over the loopback interface.  This could
# be tightened as well, but to do so would effect some of
# the administrative functions.
restrict 127.0.0.1
restrict -6 ::1

# Hosts on local network are less restricted.
restrict 10.1.1.0 mask 255.255.255.0 nomodify notrap
restrict 10.10.10.0 mask 255.255.255.0 nomodify notrap

# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
server time-a.nist.gov

server time-nw.nist.gov

server 0.ca.pool.ntp.org
server 1.ca.pool.ntp.org
# Undisciplined Local Clock. This is a fake driver intended for backup
# and when no outside source of synchronized time is available.
#server 127.127.1.0     # local clock
fudge   127.127.1.0 stratum 10



#service ntpd restart



 ntpdate -u  0.ca.pool.ntp.org

 ntpq -p