Linux hwclock Command with Practical Examples

Introduction

In this lab, you will learn how to use the hwclock command in Linux to interact with the system's hardware clock. The hwclock command allows you to synchronize the system time with the hardware clock, as well as manually adjust the hardware clock. You will start by understanding the purpose and functionality of the hwclock command, then proceed to synchronize the system time with the hardware clock, and finally learn how to manually adjust the hardware clock.

The hwclock command is a useful tool for managing the system's time and ensuring that it is accurately maintained, even when the system is powered off. By the end of this lab, you will have a better understanding of how to effectively use the hwclock command to manage your Linux system's time and clock settings.

Linux Commands Cheat Sheet

Understand the Purpose and Functionality of the hwclock Command

In this step, you will learn about the purpose and functionality of the hwclock command in Linux. The hwclock command is used to interact with the system's hardware clock, which is a battery-powered clock that keeps time even when the system is powered off.

The main purposes of the hwclock command are:

1. Synchronize System Time with Hardware Clock: You can use hwclock to set the system time based on the hardware clock, or to set the hardware clock based on the system time.
2. Adjust Hardware Clock Manually: You can use hwclock to manually adjust the hardware clock, which can be useful if the clock is drifting or needs to be set to a specific time.

Let's start by checking the current hardware clock time:

sudo hwclock

Example output:

2023-04-11 12:34:56.789012+0000

This command displays the current time stored in the system's hardware clock. The time is shown in the format YYYY-MM-DD HH:MM:SS.UUUUUU±TTTT, where YYYY-MM-DD is the date, HH:MM:SS.UUUUUU is the time, and ±TTTT is the time zone offset.

Now, let's synchronize the system time with the hardware clock:

sudo hwclock --systohc

This command sets the system time to match the hardware clock.

Synchronize System Time with Hardware Clock

In this step, you will learn how to synchronize the system time with the hardware clock on your Linux system.

First, let's check the current system time:

date

Example output:

Tue Apr 11 12:34:56 UTC 2023

Now, let's synchronize the system time with the hardware clock:

sudo hwclock --systohc

This command sets the system time to match the hardware clock. You can verify the updated system time by running the date command again:

date

Example output:

Tue Apr 11 12:34:56 UTC 2023

As you can see, the system time now matches the hardware clock time.

Adjust Hardware Clock Manually

In this step, you will learn how to manually adjust the hardware clock on your Linux system.

First, let's check the current hardware clock time:

sudo hwclock

Example output:

2023-04-11 12:34:56.789012+0000

Suppose you need to adjust the hardware clock to a different time, for example, 2023-04-11 13:00:00. You can use the hwclock command with the --set option to manually set the hardware clock:

sudo hwclock --set --date="2023-04-11 13:00:00"

This command sets the hardware clock to the specified date and time.

To verify the updated hardware clock time, run the hwclock command again:

sudo hwclock

Example output:

2023-04-11 13:00:00.000000+0000

As you can see, the hardware clock has been adjusted to the new time.

Summary

In this lab, you learned about the purpose and functionality of the hwclock command in Linux. The main purposes of the hwclock command are to synchronize the system time with the hardware clock and to manually adjust the hardware clock. You learned how to check the current hardware clock time, synchronize the system time with the hardware clock, and manually adjust the hardware clock. These skills are useful for maintaining accurate time on your Linux system and ensuring that applications and services that rely on the system time function correctly.

Linux Commands Cheat Sheet