On Fri 21 Oct 2016 at 14:28:26 (+0100), Darac Marjal wrote: > On Fri, Oct 21, 2016 at 08:09:38AM -0500, Richard Owlett wrote: > >I'm creating a preseed.cfg file for installing Debian 8.6 in a > >dual-boot enviroment with some version of MS Windows. There are > >two distinct use cases: > > [snipped] > > If you're not using NTP to provide your time, then, at boot, the > operating system will query the "hardware clock" to see what time it > is. As the hardware clock can drift, operating systems will also > set the hardware clock to match the "system clock" at shutdown time > (the system clock is the time that the operating system is using). > > The problem comes that there is no way for the hardware clock > (HWClock) to report what timezone it was set to. There are basically > two options here: > > 1. The HWClock is set to "Local Time". In this case, the operating > system sees "12:23" as being "12:23 GMT" or "12:23 CST" or whatever > and attempts no translation of the clock. > > 2. The HWClock is set to "Universal Time" (which is a > non-geographical datum time zone, with no daylight changes). In this > case, the operating system sees "12:23" as ONLY being "12:23 UTC" > and translates that into the local time zone by adding or > subtracting hours appropriately. > > If you only have one operating system on your machine, either of > these methods is fine. If you have TWO (or more) operating systems, > though, then they SHOULD agree on what the time in the HWClock > represents. If Windows thinks it's local time, but Debian thinks > it's UTC, then you'll see five-hour shifts each time you boot. > > You've already found the setting in Debian, I see, so you probably > want to check it tallies with what Windows is using. For that, look > at the Registry Key > HKLM\SYSTEM\CurrentControlSet\Control\TimeZoneInformation\RealTimeIsUniversal. > If this is 1, then the HWClock is using UTC; if it is 0, then the > HWClock is set to local time.
So what happens with the scenario: . No NTP connection, . Hardware clock running on Local Time, . Two or more OSes that know these two facts. . Neither OS was running when Civil Time changed to/from DST, . After the time changed, one OS has run, updating the Local Time to match Civil Time, . Another OS is just being booted up. What Local Time will eventually be displayed by this system? Cheers, David.
