Setting Up NTP server on CentOS 7
What is NTP
NTP (Network Time Protocol) is a protocol used to synchronize computer times over a network, and it is one of the oldest TCP/IP protocol stack parts which is highly fault-tolerant and scalable. There are thousands of NTP servers around the world with access to highly precise atomic clocks and GPS clocks, NTP uses Coordinated Universal Time (UTC) to synchronize computer clock times with precision.
Install NTP Server
First, install NTP package on your system using “yum” with the command below:
yum install ntp
Set restrict values in the configuration file
Open the NTP configuration file with your preferred text editor, we are going to use “vi”:
make sure that the following two lines are uncommented:
restrict default kod nomodify notrap nopeer noquery restrict -6 default kod nomodify notrap nopeer noquery
The restrict line allow clients to query your time server, let’s see the configured parameters:
noquery prevents dumping status data from ntpd.
notrap prevents control message trap the service.
nomodify discards all ntpq queries that attempt to modify the server.
nopeer prevents all packets that attempt to establish a peer association.
kod (kiss-to-death) packet is to be sent to reduce unwanted queries.
Allow only specific clients
To only allow machines from your network to synchronize with your NTP server, you can add the following line to your configuration file:
restrict 10.0.0.10 mask 255.255.255.0 nomodify notrap
If the localhost should have full access to every query and modify, set the line below:
Add local clock as a backup
Add the local clock to the “ntp.conf” file so that if the NTP server is disconnected from the internet, it can provide time from its local system clock.
server 127.127.1.0 # local clock fudge 127.127.1.0 stratum 10
Setup NTP log and Driftfile
declare the log and driffile location in your “ntp.conf” file:
Add the following lines, you can change location and file values as you preferred:
driftfile /var/log/ntp/ntp.drift logfile /var/log/ntp/ntp.log
The driftfile is used to log how far your clock is from what it should be, and slowly NTP should lower this value as time progress.
Start and Enable NTP server
After setting the preferred configuration parameters in the configuration file you can start and enable NTP service with the following two commands:
systemctl restart ntpd
systemctl enable ntpd