[ntp:questions] how to force NTP to use GPS

David Woolley david at ex.djwhome.demon.invalid
Mon Feb 13 22:36:53 UTC 2012

Uwe Klein wrote:
> semi OT ( either OnTopic or OffTopic ;-):
> What happens if I kill ntpd during clock slewing ?
> What happens if I SIGTERM ntpd during clock slewing ?

I don't think you have fully constrained the problem.  In some 
environments the slew will stop, although I'm not sure whether it will 
stop in about a second or when the whole slew finishes.

Without actually reading the code, I'm not sure what will happen when 
using the kernel time discipline on a system that supports it.

According to my Linux man pages, kill(2) is Posix, but adjtime(2) is 
not, so there can exist Posix compliant systems in which an ntpd 
implementation would continue to slew indefinitely if the kill was 
sufficiently hard.  (adjtimex(2) is Linux only and ntp_adjtime(2) has no 
man page and no alias in adjtimex.)

Linux implementations, at least, will retain frequency corrections in 
kernel discipline mode and lose them in user space discipline mode.

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