Time Synchronization for CentOS7

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

1. timedatectl set-timezone UTC

2. 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
      NOTE:
      This must not be a Windows Directory SNTP server.

3. Restart chrony:

   > systemctl enable chronyd
   > systemctl restart chronyd

4. 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

5. 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

6. Once the time is synchronized, sync the BIOS clock.

   hwclock --systohc