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3.3. Using the hwclock Command

hwclock is a utility for accessing the hardware clock, also referred to as the Real Time Clock (RTC). The hardware clock is independent of the operating system you use and works even when the machine is shut down. This utility is used for displaying the time from the hardware clock. hwclock also contains facilities for compensating for systematic drift in the hardware clock.
The hardware clock stores the values of: year, month, day, hour, minute, and second. It is not able to store the time standard, local time or Coordinated Universal Time (UTC), nor set the Daylight Saving Time (DST).
The hwclock utility saves its settings in the /etc/adjtime file, which is created with the first change you make, for example, when you set the time manually or synchronize the hardware clock with the system time.


In Fedora 6, the hwclock command was run automatically on every system shutdown or reboot, but it is not in Fedora 25. When the system clock is synchronized by the Network Time Protocol (NTP) or Precision Time Protocol (PTP), the kernel automatically synchronizes the hardware clock to the system clock every 11 minutes.
For details about NTP, see Chapter 14, Configuring NTP Using the chrony Suite and Chapter 15, Configuring NTP Using ntpd. For information about PTP, see Chapter 16, Configuring PTP Using ptp4l. For information about setting the hardware clock after executing ntpdate, see Section 15.18, “Configuring the Hardware Clock Update”.

3.3.1. Displaying the Current Date and Time

Running hwclock with no command line options as the root user returns the date and time in local time to standard output.
Note that using the --utc or --localtime options with the hwclock command does not mean you are displaying the hardware clock time in UTC or local time. These options are used for setting the hardware clock to keep time in either of them. The time is always displayed in local time. Additionally, using the hwclock --utc or hwclock --local commands does not change the record in the /etc/adjtime file. This command can be useful when you know that the setting saved in /etc/adjtime is incorrect but you do not want to change the setting. On the other hand, you may receive misleading information if you use the command an incorrect way. See the hwclock(8) manual page for more details.
Example 3.9. Displaying the Current Date and Time
To display the current date and the current local time from the hardware clock, run as root:
~]# hwclock
Tue 15 Apr 2014 04:23:46 PM CEST     -0.329272 seconds
CEST is a time zone abbreviation and stands for Central European Summer Time.

For information on how to change the time zone, see Section 3.1.4, “Changing the Time Zone”.