How to keep a VMWare VM's clock in sync?

Question

I have noticed that our VMWare VMs often have the incorrect time on them. No matter how many times I reset the time they keep on desyncing.

Has anyone else noticed this? What do other people do to keep their VM time in sync?

Edit: These are CLI linux VMs btw..

Answer 1

If your host time is correct, you can set the following .vmx configuration file option to enable periodic synchronization:

tools.syncTime = true

By default, this synchronizes the time every minute. To change the periodic rate, set the following option to the desired synch time in seconds:

tools.syncTime.period = 60

For this to work you need to have VMWare tools installed in your guest OS.

See http://www.vmware.com/pdf/vmware_timekeeping.pdf for more information

Answer 2

according to VMware's knowledge base, the actual solution depends on the Linux distro and release, in RHEL 5.3 I usually edit /etc/grub.conf and append this parameters to the kernel entry: divider=10 clocksource=acpi_pm

Then enable NTP, disable VMware time synchronization from vmware-toolbox and finally reboot the VM

A complete table with guidelines for each Linux distro can be found here:

TIMEKEEPING BEST PRACTICES FOR LINUX GUESTS http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1006427

Answer 3

I'll answer for Windows guests. If you have VMware Tools installed, then the taskbar's notification area (near the clock) has an icon for VMware Tools. Double-click that and set your options.

If you don't have VMware Tools installed, you can still set the clock's option for internet time to sync with some NTP server. If your physical machine serves the NTP protocol to your guest machines then you can get that done with host-only networking. Otherwise you'll have to let your guests sync with a genuine NTP server out on the internet, for example time.windows.com.

Answer 4

Something to note here. We had the same issue with Windows VM's running on an ESXi host. The time sync was turned on in VMWare Tools on the guest, but the guest clocks were consistently off (by about 30 seconds) from the host clock. The ESXi host was configured to get time updates from an internal time server.

It turns out we had the Internet Time setting turned on in the Windows VM's (Control Panel > Date and Time > Internet Time tab) so the guest was getting time updates from two places and the internet time was winning. We turned that off and now the guest clocks are good, getting their time exclusively from the ESXi host.

Answer 5

In my case we are running VMWare Server 2.02 on Windows Server 2003 R2 Standard. The Host is also Windows Server 2003 R2 Standard. I had the VMware Tools installed and set to sync the time. I did everything imaginable that I found on various internet sites. We still had horrendous drift, although it had shrunk from 15 minutes or more down to the 3 or 4 minute range.

Finally in the vmware.log I found this entry (resides in the folder as the .vmx file): "Your host system does not guarantee synchronized TSCs across different CPUs, so please set the /usepmtimer option in your Windows Boot.ini file to ensure that timekeeping is reliable. See Microsoft KB http://support.microsoft.com/kb... for details and Microsoft KB http://support.microsoft.com/kb... for additional information."

Cause: This problem occurs when the computer has the AMD Cool'n'Quiet technology (AMD dual cores) enabled in the BIOS or some Intel multi core processors. Multi core or multiprocessor systems may encounter Time Stamp Counter (TSC) drift when the time between different cores is not synchronized. The operating systems which use TSC as a timekeeping resource may experience the issue. Newer operating systems typically do not use the TSC by default if other timers are available in the system which can be used as a timekeeping source. Other available timers include the PM_Timer and the High Precision Event Timer (HPET). Resolution: To resolve this problem check with the hardware vendor to see if a new driver/firmware update is available to fix the issue.

Note The driver installation may add the /usepmtimer switch in the Boot.ini file.

Once this (/usepmtimer switch) was done the clock was dead on time.

Answer 6

This documentation solved this problem for me.

Answer 7

The CPU speed varies due to power saving. I originally noticed this because VMware gave me a helpful tip on my laptop, but this page mentions the same thing:

Quote from : VMWare tips and tricks Power saving (SpeedStep, C-states, P-States,...)

Your power saving settings may interfere significantly with vmware's performance. There are several levels of power saving.

CPU frequency

This should not lead to performance degradation, outside of having the obvious lower performance when running the CPU at a lower frequency (either manually of via governors like "ondemand" or "conservative"). The only problem with varying the CPU speed while vmware is running is that the Windows clock will gain of lose time. To prevent this, specify your full CPU speed in kHz in /etc/vmware/config

host.cpukHz = 2167000

Answer 8

VMware experiences a lot of clock drift. This Google search for 'vmware clock drift' links to several articles.

The first hit may be the most useful for you: http://www.fjc.net/linux/linux-and-vmware-related-issues/linux-2-6-kernels-and-vmware-clock-drift-issues

Answer 9

When installing VMware Tools on a Windows Guest, “Time Synchronisation” is not enabled by default. However – “best practise” is to enable time synch on Windows Guests.

There a several ways to do this from outside the VM, but I wanted to find a way to enable time sync from within the guest itself either on or after tools install.

Surprisingly, this wasn’t quite as straightforward as I expected. (I assumed it would be posible to set this as a parameter / config option during tools install)

After a bit of searching I found a way to do this in a VMware article called “Using the VMware Tools Command-Line Interface“.

So, if time sync is disabled, you can enable it by running the following command line in the guest:

      VMwareService.exe –cmd “vmx.set_option synctime 0 1″

Additional Notes

For some (IMHO stupid) reason, this utility requires you to specify the current as well as the new value

0 = disabled 1 = enabled

So – if you run this command on a machine which has this already set, you will get an error saying – “Invalid old value“. Obviously you can “ignore” this error when run (so not a huge deal) but the current design seems a bit dumb. IMHO it would be much more sensible if you could simply specify the value you want to set and not require the current value to be specified.

i.e. VMwareService.exe –cmd “vmx.set_option synctime <0|1>”