The purpose of this article is to explain how to determine the amount of time skew between an ESXi host and the associated vCenter Server, from the logs. For example, when you need to cross reference tasks and events in vCenter Server with relevant log entries in the ESXi host logs.
ESXi uses UTC exclusively for the time zone. vCenter vpxd logs include the UTC offset in the time stamp for each message. This example, from Spain, shows +01:00 as the UTC offset:
2013-11-06T12:50:30.453+01:00 [05148 info 'vpxdvpxdVmomi'] ...
To calculate the corresponding time frame in the ESXi logs, subtract the offset to acquire the equivalent time stamp to look for in the ESXi logs. For example, the equivalent ESXi log time stamp for the above vpxd extract is:
2013-11-06T11:50:30
Besides the time zone difference, there is another factor to consider when calculating time skew between vCenter Server and the ESXi host. Regular host synchronization operations occur between the vpxa agent running on the ESXi host and the vpxd daemon running on the vCenter Server. Each time this host synchronization occurs, the time is compared between them. If the time difference is more than one second (the default threshold), then the ESXi host logs the difference, in seconds to /var/log/vpxa.log.