Master Chrony: Precise NTP Time Sync on Linux Servers

Chrony Overview

Chrony is an open‑source NTP time‑synchronization tool for Unix‑like systems (Linux, BSD, macOS). It offers low latency, low CPU and memory usage, and consists of the daemon chronyd and the client utility chronyc .

chronyd : background daemon that steers the kernel clock, smooths adjustments, and synchronises with upstream servers.

chronyc : command‑line interface for monitoring and configuring the daemon, usable locally or on remote hosts.

Experimental Environment

Topology

Two servers, Server1 and Server2, are connected to the same network and can reach the Internet through NAT.

Host Details

Server1 – IP 172.16.0.134/24 – Rocky Linux 8.9 (Green Obsidian) – Kernel 4.18.0-513.5.1.el8_9.x86_64

Server2 – IP 172.16.0.150/24 – Rocky Linux 8.9 (Green Obsidian) – Kernel 4.18.0-513.5.1.el8_9.x86_64

Configuring Time Synchronization

Install Chrony

# rpm -qa | grep chrony
chrony-4.2-1.el8.rocky.1.0.x86_64

Rocky Linux 8.9 includes chrony by default; verify the installation.

Configure Server1 to sync with public NTP servers

# vim /etc/chrony.conf
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
# pool 2.rocky.pool.ntp.org iburst   # commented out
Server ntp.aliyun.com iburst          # Alibaba NTP server
Server time1.cloud.tencent.com iburst # Tencent NTP server

Restart and enable the daemon:

# systemctl restart chronyd
# systemctl enable chronyd
# systemctl is-active chronyd   # should show active

Check synchronization status:

# chronyc sources
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^* 203.107.6.88               2   6    37    63   +49us[+2956us] +/- 23ms
^- 106.55.184.199             2   6   127    60   +1891us[+1891us] +/- 47ms

The chronyc sources output columns are explained: mode (M), state (S), name/IP, stratum, poll interval, reachability, last received sample time, last sample offset, and error estimate.

Configure Server2 to sync from Server1

Edit /etc/chrony.conf on Server2 to use Server1 as a source:

# vim /etc/chrony.conf
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
# pool 2.rocky.pool.ntp.org iburst
Server 172.16.0.134 iburst

Restart and enable the daemon on Server2:

# systemctl restart chronyd
# systemctl enable chronyd

Open NTP service in the firewall:

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

Verify synchronization status on Server2 (illustrated below).

Reference: https://blog.51cto.com/min2000/8840552 (copyright belongs to the original author).