hwclock command in Linux with examples

hwclock also called Real Time Clock (RTC), is a utility for accessing the hardware clock. The hardware clock is independent of the OS(operating system) you use and works even when the machine is shut down. The hardware clock is also called a BIOS clock. A user can also change the date and time of the hardware clock from the BIOS.

The hardware clock stores the values of the second, minute, hour, day, month, and year. The hwclock utility saves its settings in the "/etc/adjtime" file, which is created when a user makes the first change.

Syntax

hwclock [function] [option...]

Key Functions of the hwclock Command

1. -r, --show

Displays the current time stored in the hardware clock (RTC).

Example:

sudo hwclock -r

2. --get

Displays the drift-corrected RTC time.

Example:

sudo hwclock --get

3. --set

Sets the hardware clock to a specified date and time. You must provide the date using the --date option.

Example:

sudo hwclock --set --date="2024-10-10 15:45:00"

4. -s, --hctosys

Syncs the system time to match the hardware clock.

Example:

sudo hwclock -s

5. -w, --systohc

Updates the hardware clock to match the system clock. This is the reverse of --hctosys.

Example:

sudo hwclock -w

6. --systz

Sends the timescale configurations (like UTC or local time) to the kernel.

7. -a, --adjust

Adjusts the hardware clock to account for systematic drift based on the drift information stored in the "/etc/adjtime" file.

8. --predict

Predicts the drift-adjusted RTC time based on the given date.

Common Options in the hwclock Command

Note: You should run the hwclock command with sudo privileges to make changes to the hardware clock or view the current RTC time.

Examples of Using the hwclock Command

1. To display the Hardware Clock Date and Time:

2. Using adjust function:

3. Using debug option to get the debug information:

Conclusion

The hwclock utility is an essential tool for managing hardware clock settings in Linux. If you're adjusting for drift, syncing system time, or simply checking the current RTC time, mastering the hwclock command can help you maintain accurate and reliable timekeeping on your Linux machine. With easy-to-use functions and options, it's a must-know utility for any Linux user or system administrator.