I've got a rig with 2 hard drives. I've put Ubuntu 9.04 (Jaunty) on one of the drives and Windows Vista SP2 runs on the other drive. I went with this approach rather than dual boot since I wanted to be able to swap out the OSes as I please and just keep things clean and separate.

The problem I've been noticing is that when I am in Ubuntu and I reboot into Windows Vista (by selecting the Vista drive at boot time), the Vista clock is always set back by about 5 hours. Also I've noticed that when I try to synchronize the Vista clock, it always errors out on the first attempt, then I have to click "Update now" a second time before the synchronization with the selected NTP server takes effect. Repeated reboots of Vista do not affect the Vista clock so long as I go from Vista back to Vista each time.

Also, the reverse is not true, that is, rebooting Vista and launching Ubuntu does not affect the Ubuntu clock.

I can't figure out why this is happening. Would appreciate any help at all.

Update: I should also probably mention that Ubunty is 64-bit and Vista is 32-bit.

  • This is an old Linux/BSD and Windows dual boot issue. I would suggest editing the question to reflect the generic nature of the problem.
    – pcapademic
    Commented May 31, 2009 at 8:54
  • Like I mentioned, the 2 OSes are not in dual boot, they're on separate SATA hard drives.
    – kpax
    Commented May 31, 2009 at 13:37
  • 1
    They are in dual boot because you boot either one or the other. Dual boot does not mean "in the same hard drive", even if that setup is the most common.
    – njsf
    Commented May 31, 2009 at 14:18
  • I always thought multiple drives each with their own OS was called a multi-boot configuration. Anyway I must be mistaken. Thanks for the clarification.
    – kpax
    Commented May 31, 2009 at 15:38

2 Answers 2


Is it this problem?

You need to look at
and change UTC=yes to UTC=no.

This makes Ubuntu read and write to the hardware clock in the same way as Windows, using local time instead of UTC.

  • Yup sounds like this is it. I'll give it a shot.
    – kpax
    Commented May 31, 2009 at 8:44
  • Ubuntu, by default will check NTP servers for the correct time, and update the system clock. Commented May 31, 2009 at 15:57

If you prefer to make the change to the windows installation:


Add a new dword named "RealTimeIsUniversal" and set it to 1

  • I'd already tried the "accepted" fix which worked for me.
    – kpax
    Commented May 31, 2009 at 13:38
  • This would have the added benefit of working if you forgot to change the timezone information after a move. Commented May 31, 2009 at 15:58
  • I've done this, but every now and then my Windows clock jumps back 6 hours (I'm UDT-6). I then have to go in and have it re-update with the time server. Commented Aug 22, 2011 at 19:12

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