[ntp:questions] ntpq -p command query

unruh unruh at invalid.ca
Thu Aug 1 19:46:27 UTC 2013


On 2013-08-01, detha <detha at foad.co.za> wrote:
> On Wed, 31 Jul 2013 08:04:53 +0000, A C wrote:
>
>> On 7/31/2013 00:26, Biswajit Panigrahi wrote:
>>> But the problem I am facing is:
>>> Whenever the connectivity between the server goes down, the status field
>>>  will not change immediately. My observation was whenever the reach
>>> field of ntpq -p command comes to zero then only the status field
>>> changes. That's why I was trying to reduce the time gap.
>>>
>>> If My approach is not correct then please suggest me the other approach.
>> 
>> You are making it far too complex and using the wrong tool for the job.
>>   If you want to know whether the connection between two machines goes
>> down, use the right tool for the job.  Tools like ping and traceroute, for
>> example, will tell you instantaneously if there is a connection problem. 
>> Use ping to probe the other server several times (assuming the other
>> server is yours.)  If you get no response, the connection failed.
>
> Ping-able network connection and a responsive ntpd on the other end is not
> the same thing. There are devices in our network that can get time from
> the primary NTP server, but not ping it, and vice versa. It all depends on
> network/firewall setup. 

It tells you that at the specific time that you sent out that query,
there was an ntpd server (not an ntp server, since not all servers are
ntpd, and thus not all servers respond to ntpq queries). But that could
simply be a brief aberation on the part of the network and your ntp
client could get a return packet every time is queries around that time. 

Network disconnections can be very transient. Do you really want to
abandona a server everytime such a blip occurs? Ssurely you want to wait
for a few poll intervals to see if the disconnection is more than
temporary. Otherwise on a busy network you could get huge amounts of
trashing as you keep changing servers. 



>
> Without a full monitoring system in place I would suggest something like
> ntpq -p server 2>/dev/null | grep '^\*' >/dev/null || echo "Fail"
>
> That will tell you that there /is/ an ntpd listening, we can talk to it,
> and it is synchronized to something. If it fails, it's time for
> ping/traceroute and tcpdump. It would have been easier if ntpq had a
> zero/nonzero exit status to check, but on at least one of my systems
> it always returns 0, success or not.
>
> -d
>



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