Ubuntu – Clock time is off on dual boot

dual-boottimezonewindows

Dual boot system Windows XP Pro and Ubuntu 12.04.

I have the bios set for the correct time and Ubuntu set for US Eastern time. Ubuntu will boot up and the time will be off by -4 hours. If I correct the time in Ubuntu then when I boot up in Windows XP the time will be off by + 4 hours.

This is a fresh install of 12.04. I did not have this problem before reinstalling Ubuntu.

Best Answer

  • https://help.ubuntu.com/community/UbuntuTime#Multiple_Boot_Systems_Time_Conflicts

    Multiple Boot Systems Time Conflicts

    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 Intrepid (8.10), UTC=yes is 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, Server 2008 R2 and Windows 8/8.1.

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

    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
    [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation]
         "RealTimeIsUniversal"=dword:00000001
    

    Note: Windows Time service will still write local time to the RTC regardless of the registry setting above on shutdown, so it is handy to disable Windows Time service with this command (if time sync is still required while in Windows use any third-party time sync solution):

    sc config w32time start= disabled
    

    Reversing the change
    You can create a file with the following contents and then double-click it to merge in the original changes, as above:

    Windows Registry Editor Version 5.00
    [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation]
         "RealTimeIsUniversal"=-
    

    If Windows Time service was disabled, enable it again with the command:

    sc config w32time start= demand
    

    Make Linux use 'Local' time

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

    Pre-Ubuntu 15.04 systems (e.g. Ubuntu 14.04 LTS):

    1. edit /etc/default/rcS
    2. add or change the following section

      # Set UTC=yes if your hardware clock is set to UTC (GMT)
      UTC=no
      

    Ubuntu 15.04 systems and above (e.g. Ubuntu 16.04 LTS):

    1. open a terminal and execute the following command

      timedatectl set-local-rtc 1
      
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