Author: Madhan Gopalakrishnan | Published on : 10-02-2025

Network Time Protocol (NTP) is crucial for keeping system time synchronized across Linux servers and Linux clients. This guide covers the installation, configuration and client-server setup for CentOS/RHEL Linux 7, 8, and 9 with details. 🚀

---

📌 Step 1: Install NTP or Chrony

👉 CentOS/RHEL 7 uses ntpd (deprecated in RHEL 8+).
👉 CentOS/RHEL 8 & 9 use chronyd (default and recommended).

For CentOS/RHEL 7 (ntpd)

yum install -y ntp

The installed package includes:

• ntpd: The NTP daemon responsible for synchronizing system time.
• ntpdate: A tool to manually sync time with an NTP server.
• ntpstat: A utility to check synchronization status.

For CentOS/RHEL 8 and 9 (Chrony)

yum install -y chrony

The installed package includes:

• chronyd: The daemon for time synchronization.
• chronyc: A command-line tool to query and modify Chrony settings.
• chrony.conf: Configuration file for defining NTP servers and rules.

---

🚀 Step 2: Enable and Start the NTP Service

For CentOS/RHEL 7 (ntpd)

systemctl enable ntpd --now

For CentOS/RHEL 8 and 9 (Chrony)

systemctl enable chronyd --now

---

🔧 Step 3: Configure NTP Servers

For CentOS/RHEL 7 (ntpd)

Edit the configuration file:

nano /etc/ntp.conf

Replace or add the following servers:

server 0.centos.pool.ntp.org iburst
server 1.centos.pool.ntp.org iburst
server 2.centos.pool.ntp.org iburst
server 3.centos.pool.ntp.org iburst

Restart the service:

systemctl restart ntpd

For CentOS/RHEL 8 and 9 (Chrony)

Edit the Chrony configuration:

nano /etc/chrony.conf

Add or modify the following lines:

server 0.centos.pool.ntp.org iburst
server 1.centos.pool.ntp.org iburst
server 2.centos.pool.ntp.org iburst
server 3.centos.pool.ntp.org iburst

Restart the service:

systemctl restart chronyd

---

✅ Step 4: Verify Synchronization

Check if NTP is syncing correctly.

For CentOS/RHEL 7 (ntpd)

ntpq -p

For CentOS/RHEL 8 and 9 (Chrony)

chronyc sources -v

Check system time:

timedatectl status

---

🔥 Step 5: Allow NTP Through Firewall

firewall-cmd --add-service=ntp --permanent
firewall-cmd --reload

---

🏢 NTP Server and Client Configuration

📡 Server Configuration (NTP Master)

Edit the NTP configuration file.

For CentOS/RHEL 7 (ntpd)

nano /etc/ntp.conf

Uncomment or add:

restrict default nomodify notrap noquery
restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap
broadcast 192.168.1.255

Restart the service:

systemctl restart ntpd

For CentOS/RHEL 8 and 9 (Chrony)

nano /etc/chrony.conf

Add:

allow 192.168.1.0/24
local stratum 10

Restart the service:

systemctl restart chronyd

---

🖥️ Client Configuration

For CentOS/RHEL 7 (ntpd)

Edit /etc/ntp.conf:

server 192.168.1.1 prefer iburst

Restart the service:

systemctl restart ntpd

For CentOS/RHEL 8 and 9 (Chrony)

Edit /etc/chrony.conf:

server 192.168.1.1 iburst

Restart the service:

systemctl restart chronyd

---

📊 Check Time Synchronization

For CentOS/RHEL 7:

ntpq -p

For CentOS/RHEL 8 and 9:

chronyc tracking

---

🎉 Congratulations! Your NTP server and clients are now synchronized! 🚀