Time of systemclock local or utc and how does time sync work?

R

RamonS

Junior Member
Having the following questions

  1. What system clock time is reported by Parallels, UTC or Local?
  2. How does time sync work and does require Parallels Tools?
  3. Can host/guest clock drift occur when sync is disabled?


What system clock time is reported by Parallels, UTC or Local?

What time is reported by Parallels when a (windows) guest retrieves the system clock value?
  • UTC
  • Local

It is unclear to me which value is returned. It would be nice if this would be configurable. I think it communicates the Local time which makes sense for most Windows installations unless the RealTimeIsUniversal registry key is set to '1' which is very useful especially when working in different timezones.

How does time sync work and does require Parallels Tools?

Second, what happens if I have time sync enabled with these two options?
  • Sync from OS X
  • Sync from either OS

I observe that I sometimes see the timezone change too. I have Sync from OS X selected.

  1. Does it set the guest OS time?
  2. Does is set the system clock?
  3. Does it set the guest timezone?
  4. What is the role of Parallels Tools, does time sync work without having it installed?


Can host/guest clock drift occur if sync is disabled?
If there is no sync enabled and internet time sync (NTP) is disabled:

  1. Will the difference between the guest and host be equal or can this value drift?
  2. What happens when the VM is suspended and resumed? What time will be reported from the system clock?



I would like to have the following behavior:

  • System clock should report the datetime value in GMT/UTC
  • Windows RealTimeIsUniversal registry key set to 1
  • I don't want Parallels to change the timezone

Is this possible? I have RealTimeIsUniversal set to 1 because I sometimes boot via Bootcamp to get the correct clock value.


References

Documentation:
http://download.parallels.com/desktop/v7/update3/docs/en/Parallels Desktop User's Guide/33243.htm

KB articles:

Time zone/clocks in Virtual Machine is out of sync with Mac OS time zone
Time synchronization works improperly
Windows virtual machine time constantly changes when Time Synchronization is turned
 
By the way, my observations:

  • Running Parallels 10 (10.2.2)
  • Window guest.
  • Windows RealTimeIsUniversal registry key is set to 0
  • OSX is set to GMT+1+DST (currently GMT+2, CEST, Amsterdam)
  • Current time in OSX 10:30am (GMT+2)
  • When the guest is booted, the time is 9:30am
  • Guest time is automatically adjusted to 10:30am (by either internet sync or parallels tools?)
  • Timezone in guest is correct (Amsterdam)

Due to the time during boot not being correct this completely messes up the timestamps in the windows event log.

This identifies that the system clock value is not UTC nor Local time (GMT+2) but GMT+1. It is very weird how that clock value is used.
 
Answers for your questions

  1. What system clock time is reported by Parallels, UTC or Local? Depends upon the configuration, Mainly as per the Mac OS X by default
  2. How does time sync work and does require Parallels Tools? Yes. It does need Parallels Tools as it is communicating with the Mac OS X for time synchronization.
  3. Can host/guest clock drift occur when sync is disabled? Yes. But if you do enable the internet time, you should be fine. Still it depends upon the Guest OS configuration as well.
 
ManojK@Parallels said:
Answers for your questions
  1. What system clock time is reported by Parallels, UTC or Local? Depends upon the configuration, Mainly as per the Mac OS X by default
Click to expand...

So system clock of guest is directly mapped to the system clock of the host? OS X stores UTC so this means that UTC would be reported to the guest?
 
ManojK@Parallels said:
Answers for your questions
  1. Can host/guest clock drift occur when sync is disabled? Yes. But if you do enable the internet time, you should be fine. Still it depends upon the Guest OS configuration as well.
Click to expand...

If I don't enable any kind of sync can clock drift happen in the VM? Meaning, that the system clock time in the VM guest is different from the VM host?
 
Time sync is a mess on my system!

Parallels is not providing the correct systemclock time to my Windows guest VM. Its not Local time and its not UTC so useless!

What I did is I temporarily disabled Parallels time sync and rely on internet time sync. You probably want to sync pretty often and not once a week which is the default time sync interval. For this you will need to update the SpecialPollInterval registry key as explained here:

I update my guest clock each 15 minutes. This is needed as Parallels Tools seems to still mess around with my guest system clock even though its disabled.

By the way, I sync with my local server! Its probably not recommended to sync with an internet time server each 15 minutes. That update frequency is probably way too high and could maybe get my banned!
 
The time issues are caused by the EFI setting. My VM is a bootcamp imported machine that requires EFI to boot. A fresh VM without EFI does not show any issues and a fresh VM using EFI has the exact same time issues as my bootcamp imported VM.
 
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