windows - Clock time is off on dual boot - Ask Ubuntu

dual boot system windows xp pro , ubuntu 12.04.

i have bios set correct time , ubuntu set eastern time. ubuntu boot , time off -4 hours. if correct time in ubuntu when boot in windows xp time off + 4 hours.

this fresh install of 12.04. did not have problem before reinstalling ubuntu.

https://help.ubuntu.com/community/ubuntutime#multiple_boot_systems_time_conflicts

multiple boot systems time conflicts

operating systems store , retrieve time in hardware clock located on motherboard can keep track of time when system not have power. operating systems (linux/unix/mac) store time on hardware clock utc default, though systems (notably microsoft windows) store time on hardware clock 'local' time. causes problems in dual boot system if both systems view hardware clock differently.

the advantage of having hardware clock utc don't need change hardware clock when moving between timezones or when daylight savings time (dst) begins or ends utc not have dst or timezone offsets.

changing linux use local time easier , more reliable changing windows use utc, dual-boot linux/windows systems tend use local time.

since intrepid (8.10), utc=yes default.

make windows use utc

note: method not supported on windows vista , server 2008, came vista sp2, windows 7, server 2008 r2 , windows 8/8.1.

to make ms windows calculate time hardware clock utc.

create file named windowstimefixutc.reg following contents , double click on merge contents registry:

windows registry editor version 5.00 [hkey_local_machine\system\currentcontrolset\control\timezoneinformation]      "realtimeisuniversal"=dword:00000001 

note: windows time service still write local time rtc regardless of registry setting above on shutdown, handy disable windows time service command (if time sync still required while in windows use third-party time sync solution):

sc config w32time start= disabled 

reversing change
can create file following contents , double-click merge in original changes, above:

windows registry editor version 5.00 [hkey_local_machine\system\currentcontrolset\control\timezoneinformation]      "realtimeisuniversal"=- 

if windows time service disabled, enable again command:

sc config w32time start= demand 

make linux use 'local' time

to tell ubuntu system hardware clock set 'local' time:

pre-ubuntu 15.04 systems (e.g. ubuntu 14.04 lts):

1. edit /etc/default/rcs

2. add or change following section

   # set utc=yes if hardware clock set utc (gmt) utc=no 

ubuntu 15.04 systems , above (e.g. ubuntu 16.04 lts):

1. open terminal , execute following command

   timedatectl set-local-rtc 1