[ntp:questions] what happens if ntp server jumps time BIG TIME

Chuck Swiger cswiger at mac.com
Fri Feb 10 00:16:28 UTC 2012


On Feb 9, 2012, at 4:05 PM, Chris Albertson wrote:
>> Exactly.  If the server reports a time that is further than the panic threshold from the client's clock (which defaults to 1000 seconds) then it will reject the server and exit.  A human is then expected to manually inspect the situation and set the clock to something reasonably close.  The -g flag lets you disable this sanity check.
> 
> I think what you describe applies to the case where a client NTP
> starts up and notice the time is very far "off".    But I think (??)
> the question was that the client is in sync and then the server's time
> jumps.  I thought -g only applied to start up logic.  I could be
> wrong.   This situation would never happen on a properly configured
> network.

Ah, yes, my response was in the context of client starting up when there is a single server, and it is very far off from what the client believes is the current time.  From what I recall in earlier testing, if ntpd is running and synched, and the remote side does something crazy like a multi-year jump, then it is promptly marked and ignored as a falseticker.  I'm not sure that I've ever tried doing this with just a single server specified, though.

I think that -x specifies the max deviation allowed when doing a step via settimeofday() rather than slewing the clock with adjtime(), and it is limited to a max permissible jump of 600 seconds, except for possibly a one-time "big" jump at startup allowed by -g.

Regards,
-- 
-Chuck



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