7. Deploy, Configure, and Maintain Systems

📘Red Hat Certified System Administrator (RHCSA – EX200)

1. Why Time Synchronization Is Important

In an IT environment, many systems work together across a network. If each system has a different time, several problems can occur.

Examples in an IT environment include:

Log files: Events recorded on servers must show the correct time for troubleshooting.
Security services: Authentication systems depend on accurate time.
Automation tasks: Scheduled jobs rely on the correct clock.
Clustered systems: Systems coordinating tasks must share the same time.

Because of this, Linux systems use time synchronization services to automatically correct the system clock.

2. Time Synchronization Protocol

Linux systems synchronize time using the Network Time Protocol (NTP).

Network Time Protocol

NTP allows systems to synchronize their clocks with trusted time servers over the network.

How NTP Works

A system sends a request to a time server.
The server replies with the current accurate time.
The client adjusts its clock gradually to match the server.

This process happens automatically and continuously to maintain accuracy.

3. Time Services Used in RHEL

In modern Red Hat systems, the main time synchronization service is:

Chrony

Chrony is faster and more reliable than older NTP implementations. It works well even when network connectivity changes.

Chrony consists of two main components:

Component	Description
chronyd	The daemon that runs in the background and synchronizes time
chronyc	Command-line tool used to monitor and control the service

4. Installing Chrony

In most Red Hat Enterprise Linux systems, Chrony is installed by default.

You can install it manually if needed.

sudo dnf install chrony

5. Starting and Enabling the Time Service

The chronyd service must be running to synchronize time.

Start the service:

sudo systemctl start chronyd

Enable it to start automatically at boot:

sudo systemctl enable chronyd

Verify the status:

systemctl status chronyd

Expected result: the service should show active (running).

6. Chrony Configuration File

Chrony is configured using the following file:

/etc/chrony.conf

This file defines which time servers the system will use.

Example configuration:

server 0.pool.ntp.org iburst
server 1.pool.ntp.org iburst

Explanation

Option	Meaning
server	Defines a time server
iburst	Speeds up the initial synchronization

You can add multiple servers for better reliability.

Example:

server time1.example.net iburst
server time2.example.net iburst

7. Restart Chrony After Configuration Changes

Whenever the configuration file is modified, restart the service:

sudo systemctl restart chronyd

8. Verifying Time Synchronization

Several commands are used to verify that time synchronization is working.

8.1 Check Time Settings

Use:

timedatectl

Example output:

System clock synchronized: yes
NTP service: active

Important fields:

Field	Meaning
Local time	Current system time
Universal time	UTC time
RTC time	Hardware clock
NTP service	Whether synchronization is active

8.2 Check Chrony Sources

Use:

chronyc sources

This command displays the time servers currently used by the system.

Example output:

MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^* time-server.example     2       6    377     34   -12us[ -25us] +/- 50ms

Symbols meaning:

Symbol	Meaning
*	Currently selected time source
+	Acceptable time source
–	Not currently used

8.3 Check Synchronization Status

Command:

chronyc tracking

This shows detailed synchronization statistics including:

reference server
system time offset
last synchronization

9. Managing Time Using timedatectl

The command timedatectl is used to manage time settings.

View Current Settings

timedatectl

Set Timezone

List available timezones:

timedatectl list-timezones

Set timezone:

sudo timedatectl set-timezone Asia/Dhaka

Enable NTP Synchronization

sudo timedatectl set-ntp true

Disable NTP:

sudo timedatectl set-ntp false

10. Hardware Clock vs System Clock

Linux systems maintain two clocks.

Clock	Description
Hardware Clock (RTC)	Physical clock stored on the motherboard
System Clock	Clock used by the operating system

Chrony synchronizes the system clock, and the system periodically updates the hardware clock.

11. Important Files and Components for the RHCSA Exam

Students should remember these key elements.

Services

Service	Purpose
chronyd	Time synchronization daemon

Commands

Command	Purpose
timedatectl	Display and configure time
chronyc	Monitor chrony
systemctl	Manage the chronyd service

Configuration Files

File	Purpose
/etc/chrony.conf	Chrony configuration

12. Typical RHCSA Exam Tasks

In the RHCSA exam, you may be required to:

Install Chrony
Start and enable the chronyd service
Configure a time server
Verify synchronization
Set the correct timezone
Ensure NTP synchronization is enabled

You must know the exact commands to complete these tasks quickly.

13. Example Complete Configuration Procedure

A typical configuration process might look like this.

1 Install chrony

sudo dnf install chrony

2 Edit configuration

sudo vi /etc/chrony.conf

Add server:

server time.example.com iburst

3 Enable and start the service

sudo systemctl enable --now chronyd

4 Verify synchronization

chronyc sources

timedatectl

14. Troubleshooting Time Synchronization

If synchronization is not working, check the following:

Service Status

systemctl status chronyd

Configuration File Errors

/etc/chrony.conf

Network Connectivity

Ensure the system can reach the configured time server.

Firewall Restrictions

NTP uses UDP port 123. Ensure it is not blocked.

15. Summary

For the RHCSA (EX200) exam, students must understand how Linux systems synchronize time using Chrony.

Key points to remember:

Time synchronization uses Network Time Protocol
Modern Red Hat systems use Chrony
The service responsible is chronyd
Configuration file is /etc/chrony.conf
Important commands include timedatectl and chronyc
Always verify synchronization after configuration

Correct time synchronization is essential for system logging, authentication systems, and network service coordination in enterprise Linux environments.