Linux rdate Command with Practical Examples

Introduction

In this lab, you will learn how to use the rdate command to synchronize your Linux system's time with a remote Network Time Protocol (NTP) server. The lab covers understanding the rdate command, synchronizing the system time with a remote NTP server, and automating the time synchronization process using Cron. This lab is designed to help you manage and maintain accurate system time on your Linux-based systems.

The lab starts by explaining the rdate command and how it can be used to set the system clock by retrieving the current time from a remote NTP server. You will then learn how to synchronize your system's time with a remote NTP server, such as time.nist.gov, and verify the updated time. Finally, the lab covers automating the time synchronization process using Cron, a time-based job scheduler, to ensure your system's clock remains accurate.

Linux Commands Cheat Sheet

Skills Graph

Understand the rdate Command

In this step, you will learn about the rdate command, which is used to synchronize the system time with a remote Network Time Protocol (NTP) server.

The rdate command is a tool that allows you to set the system clock on a Linux or Unix-like operating system by retrieving the current time from a remote server. This is useful when your system's clock is not accurate or needs to be synchronized with a reference time source.

To use the rdate command, simply run the following command in your terminal:

sudo rdate -s time.nist.gov

This will set the system clock to the current time provided by the time.nist.gov NTP server.

Example output:

Thu Jan  1 00:00:00 UTC 2023

The -s option tells rdate to set the system clock to the time received from the remote server. You can use any NTP server that is accessible to your system, such as pool.ntp.org or a server provided by your organization.

To verify the current system time, you can use the date command:

date

Example output:

Thu Jan  1 00:00:00 UTC 2023

As you can see, the system time has been updated to match the time provided by the remote NTP server.

Synchronize System Time with Remote NTP Server

In this step, you will learn how to synchronize your system's time with a remote NTP server using the rdate command.

First, let's check the current system time:

date

Example output:

Thu Jan  1 00:00:00 UTC 2023

Now, let's synchronize the system time with the time.nist.gov NTP server:

sudo rdate -s time.nist.gov

Example output:

Thu Jan  1 00:00:00 UTC 2023

To verify that the system time has been updated, run the date command again:

date

Example output:

Thu Jan  1 00:00:00 UTC 2023

As you can see, the system time has been synchronized with the remote NTP server.

You can also use the ntpdate command to synchronize the system time with an NTP server. The ntpdate command is similar to rdate, but it provides more advanced options for time synchronization. Here's an example:

sudo ntpdate time.nist.gov

Example output:

1 Jan 00:00:00 ntpdate[12345]: adjust time server 192.168.1.100 offset 0.123456 sec

The ntpdate command adjusts the system time based on the offset from the remote NTP server, providing a more accurate time synchronization.

Automate Time Synchronization with Cron

In this step, you will learn how to automate the time synchronization process using the Cron scheduler.

Cron is a time-based job scheduler in Unix-like operating systems that allows you to run scripts or commands at specific intervals. By setting up a Cron job to regularly synchronize the system time, you can ensure that your system's clock is always accurate and up-to-date.

First, let's create a script that will synchronize the time using the rdate command:

sudo nano ~/project/sync_time.sh

Add the following content to the script:

#!/bin/bash
sudo rdate -s time.nist.gov

Save and exit the file.

Next, make the script executable:

chmod +x ~/project/sync_time.sh

Now, let's set up a Cron job to run the script every hour:

sudo crontab -e

Add the following line to the crontab:

0 * * * * /home/labex/project/sync_time.sh

This will run the sync_time.sh script every hour on the hour (0 minutes past the hour).

To verify that the Cron job is running, you can check the system logs:

sudo tail -n 10 /var/log/syslog

Look for entries related to the rdate command, which should indicate that the time synchronization is happening as scheduled.

Summary

In this lab, you learned about the rdate command, which is used to synchronize the system time with a remote Network Time Protocol (NTP) server. You first understood the basic usage of the rdate command, including how to set the system clock using a remote NTP server like time.nist.gov. You then learned how to verify the updated system time using the date command. Additionally, you explored the alternative ntpdate command for synchronizing the system time with an NTP server.

Linux Commands Cheat Sheet