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I have Arch Linux + Windows 8 on my laptop. In previous versions of Windows, there is a DWORD in the registry (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation\RealTimeIsUniversal) that switches between localtime and UTC, but this doesn't seem to be working in Windows 8 anymore.

I am now getting UTC time in Windows since it thinks BIOS gives it localtime which is actually UTC time, and after reboot into Arch Linux, the clock becomes localtime-0400, because Arch thinks BIOS is having the correct UTC time.

I do not want to let Arch Linux use localtime. Under this prerequisite, is there any possible solution?

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The RealTimeIsUniversal key worked fine for me, dual booting Arch Linux also. –  numbers1311407 Nov 22 '12 at 17:23

5 Answers 5

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RealTimeIsUniversal is really buggy and not an officially recommended solution (maybe that's why they disabled it in Win8?) See IBM PC Real Time Clock should run in UT and a response from Raymond Chen here: Why does Windows keep your BIOS clock on local time?. As of date I don't think there's a proper solution for this.

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buggy? never had any problems with it, and forcing windows to use a UTC system clock really is the only sane solution. and the key is not disabled in win8. real solution is to set the registry key, turn off windows’ time sync, and let linux handle the syncing if you boot there often enough. –  flying sheep Jan 8 '14 at 19:19
@flyingsheep Over the years a few hotfixes have been released, see Current support status in Windows on cl.cam.ac.uk/~mgk25/mswish/ut-rtc.html –  Stijn May 12 '14 at 21:16

The default Windows Time service will always write local time to the hardware clock on shutdown, regardless of what the registry says about the real time being in UTC. Outside of this caveat, Windows will treat the hardware time clock correctly, if the registry is set correctly. Try this:

  1. If the time is messed up from trying to get Windows to use UTC, boot into Windows, and set the time as it would be normally (correct timezone, no regedit, Windows Time service enabled, recently synced, etc)
  2. Do the regedit you mentioned already
  3. Sync the time w32tm /config /update
  4. Disable Windows Time service sc config w32time start= disabled
  5. Install a 3rd party NTP client
  6. Verify that it works with a reboot
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Just set this up myself after having Windows set the clock on each shutdown. Found the following NTP software for Windows which is very easy to setup and configure. meinbergglobal.com/english/sw/ntp.htm –  Dracs Sep 5 '13 at 5:19

RealTimeIsUniversal registry key still works in Windows 8 and 8.1! Just tested it by myself. The instructions to use this method are explained lot of times everywhere, for example in this answer.

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@jiehanzheng yes, if you use NTP in Windows, it will mess up the clock. Sounds like the best workaround is to run NTP in whatever flavor of *NIX you're dual booting, disable NTP in Windows, and offset using whatever time zone you need to. Then you just have to adjust daylight savings time manually with a time zone shift in Windows, but eh..

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You could just set your time-zone four hours off.

enter image description here

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Smart workaround... but the hardware and system clock will be messed up again when I use NTP (Internet Time), right? –  jiehanzheng Oct 28 '12 at 17:46

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