[ntp:questions] Tricking NTP's driftfile

Steve Kostecke kostecke at ntp.org
Wed Jun 25 01:06:59 UTC 2008

On 2008-06-24, David J Taylor <david-taylor at blueyonder.co.uk> wrote:
> Steven wrote:

>> While the master goes through its synchronization routine (~10 mins),
>> the slaves cannot obtain the time (see below). Even after the master
>> is responsive, the drift file is not written to.
> Why does the master take that long?

Using the current stable release of NTP (4.2.4) the Undisciplined Local
Clock syncs after 4 "polls". The first "poll" occurs shortly after ntpd
starts; let's say at ~ 10 seconds. The next three polls occur at
minpoll. So with the default poll of 64 seconds ntpd needs:

10+(3*64) or ~ 202 seconds or ~ 3 min 22 seconds to declare the
Undisciplined Local Clock to be "synced".

If minpoll is reduced to 16 seconds (minpoll 4) the Undisciplined Local
CLock "sync time" is:

10+(3*10) or ~ 40 seconds

IIRC recent NTP-dev releases now immediately "sync" to the Undisciplined
Local Clock at startup.

Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/

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