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Old 02-17-2007, 07:26 AM   #1
Larry Webb
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Daylight Savings Time Change?


On a dual boot system if the software for one OS has the upgrade for the time change will it change the time on the other OS. If so what happens when the second OS thinks its time to change the time?
 
Old 02-17-2007, 07:55 AM   #2
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Dual OS. Windows and Linux. Linux and OS/390? MacOS and Windows?


Dissimilar operating systems won't share information about timezones.

Even with Linux and Linux unless they share the same /etc/localtime and the timezone files then changing one won't have any effect on the other. You're probably not sharing these directories.

That is to say you need to update both OSes.

Your question sounds like it is prompted by a misunderstanding of time and timezone. On UNIX/Linux time is stored as UTC (a/k/a GMT or Zulu). Timezone on the other hand is what is used to determine how the system sees the time. For example for EST5EDT timzeone there is an offset of 5 hours from UTC for EST (and 4 hours for EDT).

Translation: Changing timezone is not the same as changing time.
 
Old 02-17-2007, 09:09 AM   #3
Larry Webb
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The operating systems are XP and Suse, what brought this question to mind was when you do a new install it picks time up from (bios I thought)and times when I go back to bios the time was changed, but that was with an Windows only install and not a dual boot. If this assumption isn't correct, when I enter bios which time would it read?

Last edited by Larry Webb; 02-17-2007 at 09:11 AM.
 
Old 02-18-2007, 02:24 AM   #4
MensaWater
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Very odd. I'd replied to this before but it didn't post.

Anyway: Previously I'd noted there is a difference between time zone and time. Now I'll note there is a difference between hardware clock time and "system" time. On boot your system gets it's system time from the hardware clock. As noted though in UNIX/Linux system time is actually stored as UTC rather than your local time. It is the timzeone information that determines how it is DISPLAYED.

I would recommend doing the following in Linux:
1) Use the date command to set your system time (using your current timezone time - it will be stored in UTC in the background).
2) Use the "hwclock -systohc" command to set your hardware clock to the system time.
3) Apply your DST changes (3 really has nothing to do with 1 and 2 but needs to be done before the Mar 11th time change if you're in the U.S. or one of the other countries adjusting their DST then).
4) Reboot into XP and see if the time is OK there.
 
Old 02-18-2007, 07:24 AM   #5
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Thank you, appreciate your patience with me and for taking the time.
 
Old 03-10-2007, 04:35 PM   #6
mslolo111
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what should the linspire customers do about the new daylight savings time ?
 
Old 03-11-2007, 03:21 AM   #7
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Sorry don't use Linspire so not familiar with it.

Doing a Google search for "linspire" and "DST" pulled up a lot of hits. You may want to try that.

Even if you didn't figure it out ahead of time don't say to yourself "well it's already too late" or you'll have to manually deal with it in April again then in October then again next March etc...
 
Old 03-11-2007, 03:08 PM   #8
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The only issue could be if both Windows and Linux try to change the time, and you end up doubling it. I'd try booting into Windows first (since it will probably try to change the clock) then boot into Linux. If the time is still wrong, I'd then just go to BIOS and fix it manually

Last edited by J.W.; 03-11-2007 at 03:12 PM.
 
  


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