How to check and correct the hardware clock of the Linux System ?

Lets see how to check and correct the hardware clock of the system in case its wrong or not synced with system clock.

 

I. Check hardware and system clock of your system

[root@cavium11 log]# hwclock
Wed 06 Apr 2022 05:41:53 AM EDT  -1.000377 seconds

[root@cavium11 log]# date
Wed Apr  6 01:38:56 EDT 2022 

 

II. Solution
Here we can see the hardware clock has different time than software clock.

Hence we can sync the hardware clock to the system clock and the issue should be resolved.

# hwclock -systohc --debug

 

III. Other Options
a. In case we want to sync hardware clock to system clock, i.e. in reverse order, we can try below command.

 hwclock -hctosys --debug

b. Understanding /etc/adjtime file and adjusting hardware clock.
When our system boots, it takes the time from hardware clock.
We can adjust the hardware clock using this file.

[root@ngelinux001 ~]# cat /etc/adjtime
-0.000017 1643268372 0.000000
1643268372
LOCAL
[root@ngelinux001 ~]#

First Line
-0.000017 1643268372 0.000000
-0.000017 is the drift rate in seconds per day.
1643268372 number of seconds since 1969 UTC
0.000000 All zeros.

Second Line
1643268372 number of seconds since 1969 UTC, same as second column above.

Third Line
LOCAL –> it says either LOCAL or UTS.

 

c. Setting Hardware clock

[root@ngelinux001 ~]# hwclock --set --date "01/05/2022 22:41:15"

[root@ngelinux001 ~]# hwclock
Wed 05 Jan 2022 10:41:19 PM IST  -0.797284 seconds

 

d. Running the hwclock command in test mode.
We can also run the hwclock command in test mode, so it will not make any changes.
And will run in test mode.

# hwclock --adjust --test --debug

Similarly you can use this “test” option with any hwclock command.

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