How to use the command 'hwclock' (with examples)

The hwclock command is used for reading and changing the hardware clock time. It is typically used with root access and is useful during system setup or troubleshooting hardware-related issues. The command can display the current time as reported by the hardware clock, write the current software clock time to the hardware clock, and write the current hardware clock time to the software clock.

Use case 1: Display the current time as reported by the hardware clock

Code:

hwclock

Motivation: Displaying the current time as reported by the hardware clock can be helpful in determining the accuracy of the hardware clock, especially when troubleshooting time-related issues or during system setup.

Explanation: This command does not require any arguments. It reads the hardware clock and displays the current time as reported by the hardware clock.

Example output:

Thu 06 Oct 2022 10:15:42 PM EDT  -1.829081 seconds

Use case 2: Write the current software clock time to the hardware clock

Code:

hwclock --systohc

Motivation: Writing the current software clock time to the hardware clock is useful during system setup or when the hardware clock needs to be synchronized with the software clock.

Explanation: The --systohc option is used to write the current software clock time to the hardware clock. This command ensures that the hardware clock reflects the current system time.

Example output: No output is displayed if the command is successful.

Use case 3: Write the current hardware clock time to the software clock

Code:

hwclock --hctosys

Motivation: Writing the current hardware clock time to the software clock can be necessary in cases where the hardware clock is inaccurate or needs to be synchronized with the software clock.

Explanation: The --hctosys option is used to write the current hardware clock time to the software clock. This command ensures that the software clock reflects the current hardware clock time.

Example output: No output is displayed if the command is successful.

Conclusion:

The hwclock command is a versatile tool for managing the hardware clock time. Whether you need to display the current hardware clock time, synchronize the hardware clock with the software clock, or vice versa, the hwclock command provides the necessary functionality.