It's Fudge Time ...
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Posted: 8 Mar 2005
A reader recently asked:
Perhaps an experienced (somewhat expert) person can explain what the "fudge" statement in the ntp.conf file snippet below does:
server xxx.xxx.xxx.xxx prefer fudge 127.127.1.0 stratum 1
I am researching the best way to configure NTP in a mixed platform eDirectory environment, so that time can be synchronized as precisely as possible.
The desired structure in a designated Internet Unix host takes NTP time from another in our DMZ. That one in turn gets NTP time from an Internet time source. All other internal UNIX, NetWare, and Windows hosts will use this internal NTP host as their authoritative time source.The problem OS will be W2K and W2K3, with their convoluted "SNTP" implementation. Windows 2K does not seem to sync with the same precision as NetWare and UNIX do when using NTP.
And here's the response from one of our forum experts ...
To start ntpd, use this command:
# ntpd -p /var/run/ntpd.pid
Note: On FreeBSD-4.0, they have dropped the leading 'x', so the command is just ntpd.
To make ntpd start each time FreeBSD boots, add this to /etc/rc.conf:
Configuring the monitoring PC is a little more complicated. We have to tell ntpd that the monitoring PC's internal clock is "correct." This is done with a "fudge" line:
driftfile /etc/ntp.drift server 172.16.0.1 server 127.127.1.0 fudge 127.127.1.0 stratum 10
In this case, there are two "servers." One is another host (172.16.0.1), and the second is the internal clock. The internal clock is fudged to have stratum 10. If the other server has a higher stratum, then it takes precedence. This allows us to disconnect and reconnect the monitoring PCs from a network without affecting clock stability.
You don't need to have an external server on the monitoring PC if you don't want to. If you want all clocks to to be synchronized with a global time source, then you do want it. However, the most important thing is to have all cluster members synchronized with each other, but not necessarily to the correct time.