[ntp:questions] Lost synchronization on 2003 to 2004 year rollover

William Brower wbrower at ll.mit.edu
Thu Jan 8 01:16:11 UTC 2004

We have 7 linux machines (stock Redhat7.2, kernel 2.4.7-10smp) 
synchronized to a single NTP server on a LAN (a Datachron model 2000 
netsync server). Each of the client machines now show the correct time, 
but the incorrect date - they are all 1 day in the future.
NTP version 4.1.0 on the Linux machines.

We peeked in the logs (/var/log/message*) to see the suspicion of year 
rollover was confirmed: that is indeed the problem. About 10 minutes 
after year rollover, the ntp daemon lost synchronization with the server 
and adjusted the time by 86399.999xxx seconds. The NTP server is today 
showing the correct date and time and we have no reason to believe it 
misbehaved during rollover. We're leaning toward an ntpd bug. Suggestions?

Now a second question. Given that the NTP server is correct and that a 
client machine is 24 hours ahead of it, why does the NTP daemon not 
reject the server as "very wrong"? ntpd shows no signs of trouble even 
though the server and local machine are 24 hours different.

Note that we have a strange situation here, as all of these client 
machines and the server live on a very isolated network - and the one 
NTP server is all we have. Could this be why the machines wont reject 
the "wrong" time...that they don't have anything to compare it to? But, 
if it wont reject it, then why do the clients continue to show the wrong 
date? Shouldn't they be slewing backwards to get to yesterday?

Please CC: wbrower at ll.mit.edu


William Brower
MIT Lincoln Laboratory
Reagan Test Site, Kwajalein, Marshall Islands
p: 805.355.1310
f: 805.355.1701

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