Master Chrony: Fast, Precise Time Sync for Linux Servers

What is Time Synchronization

Time synchronization aligns a host’s clock with an external reference so that all machines in a network share a common time base. Differences in hardware clock rates cause drift, making periodic correction necessary.

Why Synchronize

Coordinated tasks in multi‑host environments (e.g., LNMP stacks) require consistent timestamps.

Incorrect timestamps can break HTTPS verification or log correlation.

Directly contacting public NTP servers from many hosts adds latency and bandwidth consumption; a local time server mitigates these issues.

How Synchronization Works

Traditional NTP adjusts the clock in large steps, which can cause gaps in file timestamps. Chrony, a modern NTP implementation, slews the clock gradually, achieving convergence within seconds or milliseconds.

Chrony Overview

Chrony implements the NTP protocol and can act as both server and client.

It consumes minimal CPU and can fall back to ntpdate compatibility.

It allows other hosts on the local network to obtain time from it.

Installing Chrony

yum install chrony -y

Key files:

Configuration: /etc/chrony.conf Client binary: /usr/bin/chronyc Daemon:

/usr/sbin/chronyd

Typical chrony.conf Settings

# Remote NTP pool 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

# Record drift
driftfile /var/lib/chrony/drift

# Fast step if offset > 1 s
makestep 1.0 3

# Enable RTC sync
rtcsync

# Allow local network
allow 192.168.0.0/16

# Serve even without external sync
local stratum 10

# Log settings
logdir /var/log/chrony
log measurements statistics tracking

Modify the file to point to internal NTP sources (e.g., server ntp1.aliyun.com iburst) and permit the desired subnet (e.g., allow 172.16.1.0/24).

Applying Changes

systemctl restart chronyd

Client Usage

Manual sync with ntpdate or chronyc -a makestep.

Automatic daemon sync via chronyd running in the background.

Verifying Synchronization

chronyc sources

Output shows the number of sources and their status, confirming that the local server (e.g., 172.16.1.62) is being used.