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Hardware (CMOS/BIOS) Clock and System Time

Requirements and recommendations

rsyslog and Kibana time stamped indices use your selected time range to create a list of indices that match a specified timestamp pattern. Please also note that rsyslog indices should rollover at midnight UTC.

Therefore it is strongly recommend that the Hardware (CMOS/BIOS) clock, system and local time is set to UTC/GMT before first boot!

Coordinated Universal Time

UTC (Coordinated Universal Time) is the international time standard. It is the current term for what was commonly referred to as Greenwich Meridian Time (GMT). Zero hours UTC is midnight in Greenwich, England, which lies on the zero longitudinal meridian. Coordinated Universal Time is based on a 24 hour clock; therefore, afternoon hours such as 4 pm UTC are expressed as 16:00 UTC.

System time

It is strongly recommend that the system clock (as well as the CMOS/BIOS clock) is set to UTC/GMT.

System time and date:

timedatectl status

This way Linux can keep the user space clock on the correct time when the change for Daylight Saving Time occurs. The safest way is to set the CMOS clock to UTC before beginning the installation process.

Reading the clock

Reading the clock:

hwclock --show ; date ; date -u

The commands above show, in succession:

  • CMOS time (should be UTC)
  • Local system time (should be UTC)
  • UTC system time

Is your system time synchronized and up to date?

One of the quickest commands to verify that ntpd is still up and running as desired is:

ntpq -p

To compare time offsets between local system time and time taken from your ntp server:

ntpdate -d server

To synchronize your system time manually:

systemctl stop ntp.service
ntpdate server
systemctl start ntp.service