[ntp:questions] Query about NTP accuracy

Garrett Wollman wollman at bimajority.org
Mon May 25 01:13:08 UTC 2009


In article <ywn9zld20zs5.fsf at ntp1.isc.org>,
Harlan Stenn  <stenn at ntp.org> wrote:

>I agree that ntpd -g is usually better than sntp (or ntpdate) to initially
>set the time, but the choice is between "Set the clock well, even if it
>takes a little time" and "Set the clock as quickly as possible and it may be
>wrong."

What is actually needed at boot time is usually neither of these
things.  It's more like "if the clock needs to be stepped backwards,
figure this out as quickly as possible, before any important services
start, accepting that there is some small chance that an additional
step in either direction may be required."  It's a straightforward
trade-off of the sort engineers make all the time: there's a limit to
how much one is willing to pay (in initiailization time) to reduce the
likelihood of post-startup nonmonotonicity.  This limit varies
depending on the application.

-GAWollman
-- 
Garrett A. Wollman   | The real tragedy of human existence is not that we are
wollman at csail.mit.edu| nasty by nature, but that a cruel structural asymmetry
Opinions not those   | grants to rare events of meanness such power to shape
of MIT or CSAIL.     | our history. - S.J. Gould, Ten Thousand Acts of Kindness




More information about the questions mailing list