Monday, 11 May 2009

Daylight savings Time Discrepency on the Apple Macs

I originally had a problem back in 2009 with time being one hour ahead or behind on OS X on dual boot macs. Happened after daylight savings time. As it happens OS X and Windows saves the time to the internal clock differently during daylight savings time. One uses gmt and adds/minus' the time accordingly and the other saves the time as absolute (if that makes sense?)

So, heres the quick fix I found for windows to act more like OS X:

’m having problems at the moment with the Apple macs, specifically the Dual Boot ones with time discrepancy. Basically, ever since the clocks have gone forward, the macs intermittently show time one hour in front and don’t let anyone log it. It only updates its time through the time server once someone has logged in (handy).

It turns out it is due to the different ways windows and OSX handle the internal clock and daylight savings. Windows sets the clock at GMT and adds 1 hour during daylight savings. OS X changes the internal clock to the daylight savings (or the other way around). So either one or the other is always out by one hour. Of course Windows always wins because it updates the clock before login and Mac users can’t login to update the clock back.

Apparently the easiest way to fix this is to modify windows to read the clock time like os x does. There are two steps:
1. Change/add a registry entry in Windows:
     RealTimeIsUniversal   = 1
2. Stop the Apple Time Service from running

Found this out here ->

I’ve got around 60 Macs I need to do this to, and was wondering if you guys have got any ways of doing these things on mass?

Otherwise I’ll have to write a batch file I think?

Thanks in advanced


Mark later wrote a script which fixed it and ran it from his SMS server.

Microsofts knowledge base article of how to set the time server stuff up:

Also found this helpful advice on changing registry quickly, and this one on command line arguments

Just ran the scripts mentioned earlier. Once Windows is "fixed", reboot into OS X, set it to the right time and all should be well.