[ale] Daylight Savings Time

[aaron]

On Wednesday 26 April 2006 12:12, Christopher Fowler wrote:
> Can someone tell me how Linux adjusts for daylight savings time?  I'm
> finding a few of my boxes an hour behind.  Their TZ is EDT and all
> of them run NTPD.  So NTP is syncing to the old time.  I stop NTPD and
> run nptdate to get the correct time.

Possibly a matter of setting and flagging the hardware clock as UTC.

I just recently fixed my system (RH 7.3) so that the hardware clock is 
properly set to UTC/GMT while the system clock reflects the correct Time Zone 
/ DST offsets. My own problem was apparently due to the weirdness of my 
NewYork time zone data file being empty (?) ; not an expected point of 
difficulty. Due to the faulty time zone info, my emails were posting with 
erroneous send times and were annoying the purists who choose to
sort by that criteria.

Anyway, I found this page very useful in finding and resolving my Time issues:
   http://www.vanemery.com/Linux/RH-Linux-Time.html

I would expect the "date" and "hwclock" shell commands and Time Zone data file 
location would be consistent for newer and non RH systems as well.

> Does the system wait for a reboot to adjust?

My experience was that YES, it did require a reboot for the Time Zone settings 
to take effect, which is one of the things that helped keep me from solving 
this time puzzle when it was first called to my attention.

>  What happens at midnight
> on the Sat before a change?  Does the box go to 01:01 the minute the
> clock strikes 12:01?

The Daylight time change happens at 2:00am so it doesn't cross over a date 
line and make things even more confusing with the Fall back.  My 
understanding is that at Spring forward, the clock counts to 1:59:59 then 
clicks over to 3:00:00. At Fall back, the clock counts to 2:59:59 then clicks 
back to 2:00:00 and repeats the 2:00am hour.

HTH
peace
aaron