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Linux Guest Clock Runs Slowly on ESX Server 2 (1518)


Why does the clock in my Linux guest run more slowly than real time?


Note: For ESX Server 3, see Linux Guest Clock Runs Slowly on ESX Server 3
By default, ESX Server versions 2.x and earlier program the real timer hardware to deliver a maximum of 1000 clock interrupts per second per CPU. However, SMP-capable Linux 2.6 kernels, as well as some 2.4 kernels with vendor patches, can require a total of 2000 or more virtual clock interrupts per second; ESX Server generally cannot sustain a virtual clock interrupt rate higher than the real hardware rate.

With ESX Server 2.5, you can increase the hardware clock interrupt rate to correct this problem. To do so, perform the following steps:

  1. Connect the VMware Management Interface to the ESX Server machine, and log on as root.
  2. Click the Options tab.
  3. Click the Advanced Settings link. This opens a new window with a list of configuration parameters.
  4. Scroll to the Misc.TimerHardPeriod parameter and click the current value. This opens a new window where you can update the value.
  5. Type a new value of 333, then click the OK button to exit.

    Values other than 333 can only make the guest clock run too slow, not too fast. The period must be short enough to give the system frequent enough chances to check whether a virtual timer interrupt is due on the guest.

Neither ESX Server nor the guest need to be rebooted after changing TimerHardPeriod.

This workaround does not apply to VMware products other than ESX Server. For a similar workaround that applies to some Linux hosts with VMware Workstation or GSX Server, refer to Virtual Machine Seems Slow when Running a Particular Program (Clock Issue)

For additional information about timekeeping in virtual machines, see the following white paper Timekeeping in VMware Virtual Machines at


1518; urlz; esx3update

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