Linux always have two types of clocks, which are Hardware Clock and System Clock. Hardware Clock, also known as CMOS Clock or Real-time Clock (RTC). System Clock is the software clock used by Linux.
When the system boots up, it would get the time/date from Hardware Clock and set it to System Software Clock. This System Clock may not often accurate, and will experience some clock slipping especially high hardware resources during too many processes running. There’re only two ways to ensure the clock is accurate according NTP, either reboot your system or perform manual synchronization.
To check your current date & time
root:/home# date
Tue Apr 20 07:45:44 PDT 2010
To change the system software clock manually
root:/home# date 042022462010.00
Tue Apr 20 22:46:00 PDT 2010
Format : date <MMDDHHmmYYYY.ss>
To ensure if your system time zone is configured correctly
( Only perform these steps if time/date is NOT CRITICAL on your system, else skip this step )
root:/home# /etc/network/if-up.d /ntpdate
root:/home# date
Tue Apr 20 07:50:41 PDT 2010
It seems like the time zone is not configured properly, change your folder to /usr/share/zoneinfo
and select the most appropriate region in the following steps
To change the system time zone
root:/home# ln -sf /usr/share/zoneinfo/Asia/Kuala_Lumpur /etc/localtime
To perform synchronization to NTP using rdate
The time server can be any public NTP server that comply to RFC868
root:/home# /usr/bin/rdate -s time-a.nist.gov
To set your hardware clock time and verify
root:/home# /sbin/hwclock --show
Tue 20 Apr 2010 03:59:03 PM MYT -0.987237 seconds
root:/home# /sbin/hwclock --systohc
root:/home# /sbin/hwclock --show
Tue 20 Apr 2010 10:58:26 PM MYT -0.782410 seconds
root:/home# /etc/network/if-up.d /ntpdate
Refers : Man Page for hwclock
Cesium Atomic Clock, maintain an accuracy of 10−9 seconds per day!!
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