Can UEFI clock / system time changed by VMware?

I have a IBM X Server with UEFI setup and on the top of this, I have a VMware v5.1. I find that it is a strange combination between the UEFI Date / Time and the system date / time on VM. If I set the UEFI as local time and the time zone in VM. The time shown in VM is wrong  after reboot, i.e. with the difference of the time zone.  

What the setting should be? What is the mechanism to update the system time from UEFI to VM OS? Or vis versa, from VM OS to UEFI, if possible?
timothyhungAsked:
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Netman66Commented:
The VMs get time from the Host ESX OS (when the vmware tools are installed in the vm).  Check the tz in the ESX settings.
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timothyhungAuthor Commented:
I mean VM time being the ESX server's date/time. Also, the guest OS on the top VM aligns the date/time of the ESX server. So, I believe there are some connection between the UEFI and the ESX (VM) on the system time.
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timothyhungAuthor Commented:
Does anyone has a suggestion? Please help.
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JohnBusiness Consultant (Owner)Commented:
Look in VMware Tools on the guest machine and under Time Sync, enable the time sync setting. That should help.
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timothyhungAuthor Commented:
John,

Thanks for your response. I know I can sync my server with NTP on VM. However, I want to know the affect on UEFI / BIOS and VM (system time and time zone).

Is it possible/ doable to update the UEFI time by OS, such as VM?
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JohnBusiness Consultant (Owner)Commented:
Is it possible/ doable to update the UEFI time by OS, such as VM?

A VM (Guest) time in the BIOS of the machine which is the VMware BIOS. I think you can only sync it as I described above or as you suggest by syncing with NTP.

I do not know of any other way.
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timothyhungAuthor Commented:
Folks,

I know my question maybe a bit tedious. But I do need some idea to verify some points.
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timothyhungAuthor Commented:
John,

Agree with you.

I can understand that UEFI updates VM and then VM updates the guest OS on system time, i.e. UEFI --> VM --> Windows, or VM or guest OS can direct update the system time with NTP. This is the basic rule for hardware design, control is built from bottom to top or upward to next level. However, someone tries to convince me that VM may change the system time from VM back to UEFI in one incident. I have doubt with this. I need more evident to find out the fact.
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JohnBusiness Consultant (Owner)Commented:
I am not even sure where UEFI comes into time. UEFI = Unified Extensible Firmware Interface  and is a replacement for BIOS.  

I do not think VMware BIOS is UEFI.  And then in any event, time is a setting in any BIOS. The Guest time can be independent and set via an Internet Clock, or it can be sync'd by VMware tools Time Sync.  That is about all there is.

someone tries to convince me that VM may change the system time from VM back to UEFI in one incident.

I don't think that is possible. I do not know if it is even relevant. Time has nothing to do with UEFI so far as I know.
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timothyhungAuthor Commented:
I do not mean VMware BIOS is UEFI. I know they are different, one software and one more on hardware. In my case, the time set in UEFI/BIOS is independent from my VM.
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JohnBusiness Consultant (Owner)Commented:
I am not sure where you are trying to head.

In my case, the time set in UEFI/BIOS is independent from my VM

Of course. The HOST machine is independent of the VM (= Virtual Machine = Guest) and the time on the HOST is set by a Time Server (Internet) and not by the Guest machine.  It has always been this way right from VMware Workstation V1 (which I started with).

Can UEFI clock / system time changed by VMware?

No. As per above, the HOST machine gets its time from a Time Server and VMware does not and cannot change that.

A guest machine gets its time from the clock provided by the VMware BIOS and can be set by time sync or by internet Time Server (either one but not both simultaneously).
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timothyhungAuthor Commented:
John,

Thanks for your input. It is exactly what I understand. In fact, I need an independence to comment on the VM and UEFI as, I mentioned, someone (from big blue) said that the UEFI time may be changed by VM and caused a problem. Although we have resolve the problem at once, I still want to understand more and prevent similar situation in future.

I would accept your comment as a solution. However, there is any further comment from the floor. I would like to have for reference.

Thanks again for everyone.
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JohnBusiness Consultant (Owner)Commented:
@timothyhung - Thank you and I was happy to help you with this.
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