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3.3.3. Synchronizing the Date and Time

You can synchronize the hardware clock and the current system time in both directions.
When you synchronize the hardware clock and the system time, you can also specify whether you want to keep the hardware clock in local time or UTC by adding the --utc or --localtime option. Similarly to using --set, UTC or LOCAL is recorded in the /etc/adjtime file.
The hwclock --systohc --utc command is functionally similar to timedatectl set-local-rtc false and the hwclock --systohc --local command is an alternative to timedatectl set-local-rtc true.
Example 3.11. Synchronizing the Hardware Clock with System Time
To set the hardware clock to the current system time and keep the hardware clock in local time, run the following command as root:
~]# hwclock --systohc --localtime
To avoid problems with time zone and DST switching, it is recommended to keep the hardware clock in UTC. The shown Example 3.11, “Synchronizing the Hardware Clock with System Time” is useful, for example, in case of a multi boot with a Windows system, which assumes the hardware clock runs in local time by default, and all other systems need to accommodate to it by using local time as well. It may also be needed with a virtual machine; if the virtual hardware clock provided by the host is running in local time, the guest system needs to be configured to use local time, too.