On August 14, 2019 9:26:36 AM PDT, David Laight <david.lai...@aculab.com> wrote: >From: Theodore Y. Ts'o >> Sent: 14 August 2019 01:06 >> On Tue, Aug 13, 2019 at 10:30:34AM -0700, Linus Torvalds wrote: >> > >> > I suspect the only actual _valid_ use in the kernel for a time zone >> > setting is likely for RTC clock setting, but even that isn't really >> > "global", as much as "per RTC". >> >> As I recall (and I may or may not have been original for the original >> sys_tz; it was many years ago, and my memories of 1992 are a bit >> fuzzy) the only reason why we added it was because x86 systems that >> were dual-booting with Windows had a RTC which ticked localtime, and >> originally, the system time was fetched from the RTC in early boot, >> and then when the timezone was set, the time would be warped so it >> would be correct. > >x86 systems are very likely to have the RTC set by the bios config. >In which case it will almost certainly get set to local time. >It is certainly the default for windows installs - I don't even know >if you have any other option. > >The 'real fun' (tm) happens when a dual boot system changes from >winter to summer time. >ISTR that it is quite easy to get both (or more) OS to change the >RTC by an hour (I went home an hour early one year). >Although the x86 RTC chip has a bit defined for 'summertime', nothing >sets it (at least when I looked). > > David > >- >Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, >MK1 1PT, UK >Registration No: 1397386 (Wales)
I believe Windows 10 changed the default RTC to UTC, although perhaps only if running under UEFI. -- Sent from my Android device with K-9 Mail. Please excuse my brevity.