Time synchronization on virtual machine

Guest OS of virtual machine can synchronize time by several way, such as NTP, VMware Tools, Windows Time Service, CMOS…etc.

VMware Tools synchronize time with ESXi host when  you enable periodic time synchronization. VMware Tools time synchronization function is disabled by default, but that’s doesn’t means time synch never happens between guest OS and host. It still happens after certain operations:

  • When the VMware Tools daemon is started.
  • When resuming a VM from suspended status.
  • After reverting from a snapshot.
  • After shrinking a disk.

It can causes some problem if guest OS have different time with host, it can lead to SAP application failed due to SAP database timestamp different with guest OS.

You can completely disable the time synchronization by following step:

  • Power off the VM.
  • Add following lines to .vmx file.
    tools.syncTime = “FALSE”
    time.synchronize.continue = “FALSE”
    time.synchronize.restore = “FALSE”
    time.synchronize.resume.disk = “FALSE”
    time.synchronize.shrink = “FALSE”
    time.synchronize.tools.startup = “FALSE”
  • Save and close the file.
  • Power on the VM.

You can also refer VMware official document.

Here is also a useful KB article for timekeeping best practices for Linux VM.

 

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