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Old 10-12-2006, 07:57 AM   #1
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5 hour time difference between different configurations

Can anyone tell me what is going on?
Is there an alternative way to set the timezone?

I originally thought this issue was related to a Windows/Linux difference but now I have more information.

I have an embedded system (not a desktop) where I have a Linux development system (kernel 2.6.7 and Slackware) on a hard disk and a Linux target system (kernel 2.6.7 and BusyBox) on a Flashdisk.

Both the hard disk and the Flashdisk systems share the same processor. I can use LILO to choose which system I boot.

The system originally came to me from the West Coast and I didn't pay any particular attention to how the date/time was being displayed. Recently I decided to change the timezone setting to EDT since that is more appropriate to where I am located.

On the development system (Slackware) I found that the /etc/localtime was a symlink to /usr/share/zoneinfo/US/Pacific so I simply changed it to a symlink to /usr/share/zoneinfo/US/Eastern.
The embedded system (BusyBox) did not have a /etc/localtime file so I simply copied the /usr/share/zoneinfo/US/Eastern file from the development system and renamed it as /etc/localtime.

Both changes show the date/time as EDT when I used the 'date' command. However when I set the correct time on one system, shutdown, and restart the other system I find that the other system is showing a different time. Specifcally the development system is 5 hours ahead of the embedded system.

Is there another place that one, or other, of the systems is getting/saving the current time? They both share the same system clock so I am thinking it must be the way in which they are interpreting that information.

Last edited by idc12; 10-12-2006 at 08:36 AM. Reason: More information about the problem
Old 10-12-2006, 09:26 AM   #2
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as it's a 5 hour offset it sounds like one os is using the system clock as local time, the other is using it as UTC. As UTC is, of course, the right time, and anyone not living in UTC timezones are inherently defective () you shoul dchange both operating ssytems to treat the bios clock as UTC and not your local time zone. or ignore your shortcomings and set both to use it as local time. then you'll get no variance.
Old 10-12-2006, 03:42 PM   #3
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Thanks, you are absolutely correct.

After doing some more searching around I discovered that my development system is using 'localtime' and the target system (BusyBox) is using UTC.

Since I have to interface with Windows I am planning to change the target system over to 'localtime'. I see that to keep everything tidy I need to set the system time to the hardware clock when the system boots, and then save the system time to the hardware clock when I reboot or shutdown. I can find a way of doing the first, but I am having trouble finding any sort of reboot or shutdown script for BusyBox.

Anyone know of a way to change the way BusyBox shuts down?
Old 10-12-2006, 04:02 PM   #4
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If I understand how the system and hardware clocks are synchronized, it seems to me that a two-command step is called for to set the system time, then synchronize the hardware clock. Upon boot, the kernel (no matter which OS) will set system time to match the hardware clock.

first command:

date (plus date and time info). see the date man pages for the correct format. this will set the system time.

second command:

hwclock --hctosys. this will synchronize the hardware clock with the system time you just set in command one above.

Now, with the hardware clock set, no matter which OS you choose to boot, it should synchronize with the hardware clock.


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