Time Synchronization for CentOS7

Steps to set a server's time source to the NTP server:

Use and set the coordinated universal time, UTC.
timedatectl set-timezone UTC
In chronyd.conf, add or modify the following IP address setting.
1. When using SCS, use the Swarm-internal IP address.
  server {SCS Swarm-internal IP address} iburst
2. To use a different NTP server:
  server {NTP server IP} iburst

Important

This must not be a Windows Directory SNTP server.

Restart chrony:

> systemctl enable chronyd
> systemctl restart chronyd

Verify the time sources are correct.

chronyc sources -v

Verify there is an asterisk (*) next to one of the lines, indicating the time has been synchronized.

Example:

210 Number of sources = 1

  .-- Source mode  '^' = server, '=' = peer, '#' = local clock.
 / .- Source state '*' = current synced, '+' = combined , '-' = not combined,
| /   '?' = unreachable, 'x' = time may be in error, '~' = time too variable.
||                                                 .- xxxx [ yyyy ] +/- zzzz
||      Reachability register (octal) -.           |  xxxx = adjusted offset,
||      Log2(Polling interval) --.      |          |  yyyy = measured offset,
||                                \     |          |  zzzz = estimated error.
||                                 |    |           \
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^* telamon.tx.caringo.com        3   8   377   152  +5225ns[+7036ns] +/-   98ms

Display tracking stats for the chrony deamon.

chronyc tracking -v

The tracking command displays parameters about the system’s clock performance.

An example of the output shown below.

Reference ID    : 2D7D0114 (telamon.tx.caringo.com)
Stratum         : 4
Ref time (UTC)  : Tue Jul 26 03:49:40 2022
System time     : 0.000021030 seconds slow of NTP time
Last offset     : -0.000020990 seconds
RMS offset      : 0.000054007 seconds
Frequency       : 13.100 ppm slow
Residual freq   : -0.002 ppm
Skew            : 0.030 ppm
Root delay      : 0.004795842 seconds
Root dispersion : 0.002171046 seconds
Update interval : 1029.6 seconds
Leap status     : Normal

Once the time is synchronized, sync the BIOS clock.

hwclock --systohc