On 18-11-15 18:00:14, Joe Zeff wrote:
On 11/15/2018 03:17 PM, Rick Stevens wrote:
In Linux
case, it expects UTC. In Windows, it expects local time.
I haven't had to deal with this for years, but if memory serves,
there's a
place where you can tell Linux that the hardware clock is in local
time,
not UTC.
man hwclock:
LOCAL vs UTC
Keeping the Hardware Clock in a local timescale causes
inconsistent
daylight saving time results:
· If Linux is running during a daylight saving time change,
the time
written to the Hardware Clock will be adjusted for the change.
· If Linux is NOT running during a daylight saving time
change, the
time read from the Hardware Clock will NOT be adjusted
for the
change.
The Hardware Clock on an ISA compatible system keeps only a
date and
time, it has no concept of timezone nor daylight saving.
Therefore,
when hwclock is told that it is in local time, it assumes it is
in the
'correct' local time and makes no adjustments to the time read
from it.
Linux handles daylight saving time changes transparently only
when the
Hardware Clock is kept in the UTC timescale. Doing so is made
easy for
system administrators as hwclock uses local time for its
output and as
the argument to the --date option.
POSIX systems, like Linux, are designed to have the System
Clock oper‐
ate in the UTC timescale. The Hardware Clock's purpose is to
initialize
the System Clock, so also keeping it in UTC makes sense.
Linux does, however, attempt to accommodate the Hardware Clock
being in
the local timescale. This is primarily for dual-booting with
older ver‐
sions of MS Windows. From Windows 7 on, the
RealTimeIsUniversal reg‐
istry key is supposed to be working properly so that its
Hardware Clock
can be kept in UTC.
--
____________________________________________________________________
TonyN.:' <mailto:tonynelson@xxxxxxxxxxxxxxxxx>
' <http://www.georgeanelson.com/>
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