[ntp:questions] Can i control the NTP Sync?

David Woolley david at ex.djwhome.demon.co.uk.invalid
Wed Aug 13 06:50:47 UTC 2008

Unruh wrote:

> machnes) the machine time is ALWAYS UTC. time routines do the translation
> using a file called /etc/localtime. On windows it is more difficult, since

Not all Unixes use the Olson package and some may use a different 
location for this file.  Some Unixes, in current use, encode the rules 
in an environment variable, which needs to be changed when the rules 
change (but not when the clocks change), and thus an application 
restart. Earlier ones only allowed the base timezone offset to be 
changed but had the, historic, US timezone rules hardcoded.  I think the 
original Unix did timezones only the kernel.

You will have some problems in exchanging media between Unix systems if 
you don't run them on UTC, as file timestamps are stored in the POSIX 
encoding of UTC and converted to local time by the ls command, etc.

> Microsoft has never heard of timezones, so you have to kludge it yourself. 

Microsoft have supported timezones since Windows 9x or earlier and have 
reasonably proper support since Windows NT.  For legacy reasons, they 
store wall clock time in the RTC hardware.  Windows encodes the rules in 
the registry and the registry needs updating when the rules change, but 
I don't think you need an application restart.  (Both the older Unix 
system and NT are limited to two changes and two offsets per year.)

> Exactly how your machine or your implimentation of ntp kludges it I do not
> know.

More precisely, you always need to specify what OS you are using.  Not 
specifying in an NTP context tends to imply Linux, but Linux tends to be 
leading edge and any recent one will use the Olson package.

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