This document provides instructions for installing and configuring the Chrony time synchronization daemon on Red Hat Enterprise Linux 7 systems. It describes Chrony as an alternative to NTP that can adjust the system clock more rapidly, especially for servers that are not permanently connected to the network or powered on. The document outlines pre-requisites, advantages of Chrony over NTP, package installation steps, and commands to enable, start, and check the status of the Chrony daemon.

1. How To Install and Configure Chrony on RHEL 7
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Table of Contents
Overview.......................................................................................................................................................1
Applies To......................................................................................................................................................1
Pre-Requisites ...............................................................................................................................................1
Advantages – Chrony ....................................................................................................................................1
Disadvantages – Chrony................................................................................................................................2
Install Package...............................................................................................................................................2
Enable Chrony Daemon ................................................................................................................................3
Start Chrony Daemon ...................................................................................................................................3
Status Chrony Daemon .................................................................................................................................3

2. How To Install and Configure Chrony on RHEL 7
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Overview
This guide will help in installing and configuring chrony service.
Chrony is a different implementation of the NTP protocol than ntpd, it can adjust the system clock more
rapidly.
Ideally, we should choose Chrony over ntp, wherein the servers are not permanently connected to
physical network interface and also servers that are not permanently connected or turned on.
Applies To
 RHEL 7, CentOS 7
Pre-Requisites
 None
Advantages – Chrony
Before we implement chrony in the environment there few considerations and advantages that chrony
provides over NTP and they are listed in below table;
Chrony NTP
Servers that are not permanently connected to
the network
Servers that are permanently connected to the
network
Servers that are not permanently powered on Servers that are permanently powered on
Applications / servers that need date and time
synchronization faster
Applications / servers that can wait longer time for
synchronization of date and time
Auto correct smaller drifts and offsets Auto correction of smaller drifts and offsets is not
very critical
Temperature changes that are significantly higher,
which affect the stability of hardware clock
Temperature changes that are ideal and cool
temperature and stability of hardware clock is
always apt
Where system restarts take longer duration to
boot up depending on the environment and
application dependencies
Where system restarts doesn’t longer duration to
boot up the environment and application
dependencies are more or less doesn’t exists.
It can work well even if the external time
references are only intermittently accessible
NTP needs regular pooling of time reference to
work well

3. How To Install and Configure Chrony on RHEL 7
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Apt for systems are virtual machines, wherein
machines that are unstable or broken
Ideal for systems are physical machines, wherein
machines that are stable
Works well even if there is network congestion NTP Needs regular pooling
Synchronizes the clock faster Can’t synchronize the clock faster because it needs
regular pooling of time
Adapts quickly to sudden change in rate of clock,
temperature changes
Takes longer time to adapt to temperature
changes
Disadvantages – Chrony
Even though there are advantages in implementing chrony in the that are few drawbacks as well that are
listed in the below table;
Chrony NTP
chronyd uses NTP version 3 (RFC 1305),
which is compatible with version 4
ntpd fully supports NTP version 4 (RFC 5905), including
broadcast, multicast, many cast clients and servers, and
the orphan mode. ntpd also supports extra authentication
schemes based on public-key cryptography (RFC 5906).
chronyd relies on other programs, for
example gpsd, to access the data from the
reference clocks
ntpd includes drivers for many reference clocks
Note: Chrony can be implemented ideally on mobile or virtual systems.
Install Package
Before the chrony package is installed To install the chrony package, run the command;
yum list installed | grep chrony
yum install -y chrony

4. How To Install and Configure Chrony on RHEL 7
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Enable Chrony Daemon
After installation, we have to enable the chrony service to start at OS boot, run the
command;
systemctl enable chronyd
Start Chrony Daemon
To start of the chrony service, run the command;
systemctl start chronyd
Status Chrony Daemon
To verify the status of the chrony service, run the command;
systemctl status chronyd -l

5. How To Install and Configure Chrony on RHEL 7
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