Configuring NTP clients
	Part V. Configuring Linux subsystems

Configuring NTP clients

Jurjen Bokma

September 2007

The ntp daemon used for timekeeping may not by default be configured well for all circumstances. In particular, the “iburst” and “burst” directives may be needed in server statements in order to let the machine under config trust its external time sources well enough to let it choose these for reference instead of the local clock. And it this is not enough, the local clock (recognizable as a “127.127.something” server entry) may have to be taken out of the configuration altogether.

Example 1. Snippet from ntp.conf showing “iburst” flag to “server” statement

#server 127.127.1.0 
#fudge 127.127.1.0 stratum 10 
server 0.debian.pool.ntp.org burst iburst 
server 1.debian.pool.ntp.org burst iburst 
server 2.debian.pool.ntp.org burst iburst 
server 3.debian.pool.ntp.org burst iburst

	Local clock commented out, or it will be taken as the reference.
	“Fudging” the local clock to al (low) stratum 10 appeared not to be enough to keep it from being taken as the reference clock.
	This “(i)burst” needed here, or system clock won't be set.

This measure should result in something like the following output of ntpq -p:

remote refid st t when poll reach delay offset jitter ============================================================================== +ntp1.hro.nl 192.87.106.2 2 u 6 64 377 7.027 4007.26 838.555 *ntp2.hro.nl 193.79.237.14 2 u 60 64 377 7.068 4067.85 577.443 -ns1.iseer.nl 193.67.79.202 2 u 12 64 377 4.415 4668.18 344.353 +news.vps.budget 193.79.237.14 2 u 24 64 377 4.595 3854.39 911.959 xRN2-R6509-RP.ne 192.36.143.150 2 u 22 64 377 0.798 4824.30 259.985

If the local system is really screwed up, removing the drift file may also help.

	Note
	It may take half an hour for the daemon to reign the local clock. If the `drift` file was removed, it will only be created again after an hour of continuous operation.

Extensive documentation on ntp is available as "The Network Time Protocol (NTP) Distribution" at www.eecis.udel.edu.


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