Master Chrony: Fast, Accurate Time Sync for Linux Servers

1. Time Synchronization Basics

1.1 What is Time Synchronization

Time synchronization aligns local system clocks with Internet time, providing a unified time reference. Local clocks drift due to varying rates and environments, so periodic synchronization is required.

1.2 Why Time Synchronization is Needed

Coordinated tasks across multiple hosts (e.g., LNMP architecture) require consistent timestamps.

Incorrect timestamps can cause security issues for HTTPS and other services.

1.3 How Time Synchronization Works

Manual adjustment using date or ntpdate can cause abrupt jumps.

Traditional NTP may take minutes to correct large offsets, while Chrony adjusts more smoothly.

2. Chrony Time Service

2.1 Introduction to Chrony

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

It offers higher accuracy and faster convergence than classic NTP.

Low CPU usage and compatible with ntpdate.

Allows other hosts on the local network to synchronize with it.

2.2 Why Use Chrony

Central internal time server reduces latency and bandwidth compared to each host contacting public NTP servers.

Improves synchronization speed and reliability.

2.3 Installing Chrony

yum install chrony -y

Configuration file: /etc/chrony.conf Client program: /usr/bin/chronyc Server daemon:

/usr/sbin/chronyd

2.4 Default Configuration (excerpt)

# Use remote 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

driftfile /var/lib/chrony/drift
makestep 1.0 3
rtcsync
allow 192.168.0.0/16
local stratum 10
logdir /var/log/chrony
log measurements statistics tracking

2.5 Modifying Configuration

vim /etc/chrony.conf
# Example
server ntp1.aliyun.com iburst
server ntp2.aliyun.com iburst
allow 172.16.1.0/24
local stratum 10

2.6 Restart Service

systemctl restart chronyd

2.7 Client Usage

# Check sources
chronyc sources
# Force step correction
chronyc -a makestep