Windows, Linux dual-boot system time issues

Multiple Boot Systems Time Conflicts

From The Ubuntu Community:

Operating systems store and retrieve the time in the hardware clock located on your motherboard so that it can keep track of the time even when the system does not have power. Most operating systems (Linux/Unix/Mac) store the time on the hardware clock as UTC by default, though some systems (notably Microsoft Windows) store the time on the hardware clock as the ‘local’ time. This causes problems in a dual boot system if both systems view the hardware clock differently.

The advantage of having the hardware clock as UTC is that you don’t need to change the hardware clock when moving between timezones or when Daylight Savings Time (DST) begins or ends as UTC does not have DST or timezone offsets.

Changing Linux to use local time is easier and more reliable than changing Windows to use UTC, so dual-boot Linux/Windows systems tend to use local time.

Since Ubuntu Intrepid (8.10), the hardware clock is set to UTC by default.

Make Windows use UTC

Note: This method was not initially supported on Windows Vista and Server 2008, but came back with Vista SP2, Windows 7 and Server 2008 R2.

To make MS Windows calculate the time from the hardware clock as UTC.

Via regedit:

Run regedit and navigate to


Right-click in the right-side panel and select New > DWORD Value. Create the key named RealTimeIsUniversal and give it a value of 1.

Using a registry file

Create a file named WindowsTimeFixUTC.reg with the following contents and then double click on it to merge the contents with the registry:

Windows Registry Editor Version 5.00


Make Linux use ‘Local’ time

To tell your Ubuntu system that the hardware clock is set to ‘local’ time:

1. edit /etc/default/rcS

2. Set UTC=yes if your hardware clock is set to UTC (GMT), or UTC=no to have the hardware clock set to local time.

It’s come to my attention that this issue also affects Macs which dual boot via bootcamp or other methods. 

Questions, comments, and feedback is welcome and appreciated.


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  1. #1 by mtk on May 13, 2011 - 3:10 pm

    Hi, thanks for the help. I think this is what I was looking for; do you know, is there a way, outside of the registry, to confirm that Windows 7 is actually using the UTC time (I just don’t trust it anymore)? I was having trouble with dropbox deleting things in a dual boot environment because of Windows and Ubuntu having slightly different times, so I’m hesitant to re-enable my Ubuntu-dropbox. Thanks.

    • #2 by Mike on May 13, 2011 - 5:28 pm

      I don’t have a Windows 7 machine in front of me, but there’s a set of things you could check:

      * Check the BIOS date/time to verify it’s set to UTC (or reasonably close)
      * Check the Windows time zone to make sure it’s set to local time zone
      * Check the Windows “current” date/time to make sure it correctly reflects local time.

      That should cover verifying that Windows is correctly handling the system clock (the BIOS clock) set to UTC.

      As far as Dropbox is concerned, I actually haven’t seen this issue (I use dropbox a lot). You might want to try try uninstalling all the clients (back up your files first!) and delete files from the dropbox website, then reinstall your clients. This will reset you back to a clean slate for all the installations, and will probably clear up any issues caused by skewing the clock.

      • #3 by mtk on May 19, 2011 - 6:52 am

        Thanks, this didn’t seem to work well with Windows 7; the clock now does not keep my time zone offset, so every reboot I’m off by 6 hours. Kind of a headache. I look forward to the days when I no longer need Windows, but either way, I think it’s getting a reinstall in the near future when I have a free moment.

        The dropbox problems mostly happened with really large files and quick reboots. I ended up figuring out that Windows and linux were off by about 1 minute, so if the reboot took less than that, dropbox updated the server to say that the file had been deleted from the client.

        Anyhow, thanks for your help.

  2. #4 by penjagalab on April 4, 2012 - 6:26 pm

    • #6 by penjagalab on April 4, 2012 - 10:19 pm

      i mean : i used your trick

      • #7 by Mike Beach on April 4, 2012 - 11:19 pm

        I’m glad you found it useful :)

  3. #8 by reikred on April 16, 2012 - 6:25 pm

    The backslashes seem to be missing in the registry paths….

    • #9 by Mike Beach on April 16, 2012 - 6:55 pm

      Thanks for the heads-up on that. Should be fixed now.

  4. #10 by Jyo on July 21, 2012 - 7:49 pm

    Just tried this on Linux Mint Debian; worked perfectly. However, I find it weird how this issue never occurred when I dual booted Ubuntu in the past.

  5. #11 by Seven on June 1, 2013 - 12:27 pm

    A little late to chime in, I suppose, but this problem ‘also’ affects the ‘bios clock’ in the x64 uefi motherboard… which the windows OS then relies on verbatim. Just a thought.

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