System time is an issue of great importance to many computer applications. Databases, security monitoring tools, e-mail systems, syslog and other logging tools all use time stamps in writing transactions and/or noting various events. VMtools has an option for virtual machines to sync with the ESX host they are running on. It should be obvious that all of the ESX hosts in a given resource cluster should have their own system clocks synchronized so that when a virtual machine is vMotion'd from one ESX host to another, its system time would remain consistent.
ESX hosts include NTP software and start the ntpd service by default. ESX hosts are not configured to actually make use of NTP upon installation, nor is there anything in the standard installation process which gives the administrator a chance to set this. Proper NTP usage only occurs when the administrator is knowledgeable of NTP and its administration, and has as standard practice, configuration of NTP as one of their post-installation tasks. This is often not the case.
This article is intended for adminstrators and VMware Tech Support Engineers as a guideline to configuring ESX hosts for NTP use.
Note: For ESX 3.5 and above, NTP can be configured from vSphere Client and no longer requires manual configuration. For more information, consult the Datacenter & Cloud Infrastructure section of VMware documentation for your version of ESX.