Hwclock

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All systems maintain two different times. One is software clock which is maintained by OS when system is running. Other is hardware clock which runs even when system is powered off using CMOS cell. To look at current software clock we can use:

timedatectl

To look at current hardware clock use:

hwclock

Synchronize hardware clock with software clock

Software clock can be corrected using:

ntpdate -b <time-server>

Then same time can be copied to hardware clock using:

hwclock -w

Other way round to copy hardware clock to os clock use:

hwclock -s

Most of this information is learned from https://docs.fedoraproject.org/en-US/Fedora/22/html/System_Administrators_Guide/ch-Configuring_the_Date_and_Time.html

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