Inquiring Minds

[ME]

Sue Bennett said:
>
> I am puzzled.  I have my machine set up as a dual bootable
> machine with Windows and Linux.  Why did I have to boot up under
> Windows in order for Linux to realize that daylight savings time
> had ended?  The only thing I can think of is that since the
> machine was initially set up under Windows, and therefore
> Windows has the lower disk space that the system (hardware)
> clock is controlled by Windows.  If Linux had been the initial
> OS would Linux then control the system clock?

Windows often has access to the hardware clock on x86 machines. When
Windows is told to "Automatically Adjust the time for Daylight Savings
time" it will try to alter the hardware clock as well as the running
system's clock. This change will last between boots and Linux will see
these changes when it boots and grabs the time from the hardware clock.

When you dual boot Linux/Windows, you usually do not have your hardware
clock's time set in GMT. While it is not, most Linux systems will not
automatically adjust the local time and system time to take into
consideration daylight savings time. Users of such dual boot systems will
often use NTP to sync their local time to that of some reliable time
server(s) "out there."

Ususally, they configure the ntp update to only change the local system
time and not the hardware clock too (since the next boot in windows will
change that and lead to a double-change if changed in Linux first.
(disabling Windows auto-update of DST and having linux use NTP to update
both if you spend equal time in windows/linux, or more time in linux, is
often a good idea too.)

When Linux is the only OS, or all OS on the box like local hardware clocks
stored in GMT, then you can just configure each OS to set their local time
base on GMT and DST and set ntp to sync your hardware clock to GMT.

The short answer:
If you run dual boot win/lin, and use windows often, let windows do dst
changes and have linux *not* assume local hardware clock is in GMT.

If you mostly run Linux, examine disabling Windows control of DST and have
Linx use ntp to update the system clock *and* hardware clock frequently.

If you only use Linux, use hardware clock in GMT, and if you like reliable
time, setup ntp to update your system and hardware clocks.

References:
date, ntp, /etc/timezone, /etc/localtime
(last two are likely to be *NIX system dependent)


-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GCS/CM$/IT$/LS$/S/O$ !d--(  ) !s !a   (-----) C  $(    ) U    $( $) P $>  
 L   $(  ) E W   $( ) N  o K w $>  >    O-@ M $ V-$>- !PS !PE Y  PGP
t at -(  ) 5 @ X@ R- tv- b   DI D  G--@ e >  >     h(  )>  r*>? z?
------END GEEK CODE BLOCK------
decode: http://www.ebb.org/ungeek/
about:  http://www.geekcode.com/geek.html