Timekeeping

Last Updated : Nov 24, 2021 |
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For accurate timekeeping, use the Network Time Protocol (NTP) as a time source instead of the ESXi hypervisor.
The NTP servers can be local or over the Internet. If the NTP servers are on the Internet, the corporate firewall must open UDP port 123 so that the NTP service can communicate with the external NTP servers.
The VMware tools time synchronization method is disabled at application deployment time to avoid dueling clock masters. You must configure the NTP service first because the applications are not receiving clock updates from the hypervisor. To verify that VMware Tools Timesync is disabled, run the command /usr/bin/vmware-toolbox-cmd timesync status.
In certain situations, the ESXi hypervisor pushes an updated view of its clock into a virtual machine. These situations include starting the virtual machine and resuming a suspended virtual machine, If this view differs more than 1000 seconds from the view that is received over the network, the NTP service might shutdown. In this situation, the guest OS administrator must manually set the guest clock to be the same or as close as possible to the network time source clock. To keep the NTP service active, the clock on the ESXi host must also use an accurate clock source, such as the same network time source that is used by the guest operating system.
If you use the names of the time servers instead of the IP address, you must configure the Domain Name Service in the guest OS before you administer the NTP service. Otherwise, the NTP service cannot locate the time servers. If you administer the NTP service first, you must restart the NTP service after administering the DNS service.
After you administer the NTP service in the application, run the chronyc sources -v command from a command window. The results from this command:
  • Verify if the NTP service is getting time from a network time source.
  • Indicate which network time source is in use.
  • Display how closely the guest OS matches the network time.
  • Display how often the guest OS checks the time.
The guest OS polls the time source every 65 to 1024 seconds. Larger time intervals indicate that the guest clock is tracking the network time source closely. If the time source is local, then the NTP service is not using a network time source and a problem exists.
If the clock value is consistently wrong, look through the system log for entries regarding chronyd. The NTP service writes the activities it performs to the log, including when the NTP service loses synchronization with a network time source.