Follow VMware's advice to keep VM time from drifting

If you find the Linux virtual machines have been falling out of sync, then it's possible you need to enable a key vSphere setting.

Our Linux virtual machines lose their time syncing often. How do you keep VM time in sync?

Keeping VM time synchronized is critical to making sure such things as snapshots are created and restored at the proper time and to ensure VMs are getting the services they need when they need them.

For Linux virtual machines, VMware recommends using Network Time Protocol (NTP) synchronization to adjust the VMs to the correct time.

When you have configured NTP, disable the VMware Tools time synchronization feature if it is running. Otherwise you will have two synchronization mechanisms in contention.

In the time between NTP time synchronization intervals, the time is dependent on the "local clock" of your virtual machine. Since there is no real local clock, it's possible this is the cause of the drift.

It is a good idea to use the correct kernel parameters for your Linux distribution. The most recent distributions such as Red Hat Enterprise Linux (RHEL) 6 and SUSE Linux Enterprise Server (SLES) 11 do not need additional parameters. Since many VMware appliances are based on SLES 11, no additional configuration is necessary.

The list of Linux distributions and the proper kernel parameters can be found at the VMware knowledge base site in article 1006427 found here.

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