[ntp:questions] Re: ntpd, boot time, and hot plugging

[Richard B. Gilbert]

Tom Smith wrote:

> Brad Knowles wrote:
>
>> At 4:21 AM +0000 2005-02-04, Tom Smith wrote:
>>
>>>  # time ntpd -gq [13 servers in ntp.conf]
>>>  ntpd: time slew -0.000373s
>>>
>>>  real    1m43.03s
>>>  user    0m0.10s
>>>  sys     0m0.60s
>>
>>
>>
>>     Yes, but what does that ntp.conf look like?  Are you using 
>> iburst?  Any authentication?  Manually setting minpoll and/or 
>> maxpoll?  Did you have a good drift file to start with?
>>
>>     You need to provide some more specifics before you can make an 
>> attempt to compare this to ntpdate.
>>
>>>  # time ntpdate -b [three selected servers]
>>>   3 Feb 22:44:45 ntpdate[186032]: step time server [IP address] 
>>> offset -0.000157 sec
>>
>>
>>
>>     Not comparable.  You need to include all thirteen servers before 
>> this could potentially be considered comparable.
>>
>
> As you wish...
>
> # cat /etc/ntp.drift
> -2.653
>
> # ntpq -p
>      remote           refid      st t when poll reach   delay   
> offset  jitter
> ============================================================================== 
>
>  LOCAL(1)        LOCAL(1)         5 l   41   64  377    0.000    
> 0.000   0.004
>  [IP.255]        0.0.0.0         16 u    -   64    0    0.000    0.000 
> 4000.00
> -[name]          .TRUE.           1 u  468 1024  377   12.741   
> -0.950   0.092
> -[name]          .WWVB.           1 u  470 1024  377    1.388    
> 1.015   1.216
> -[name]          [name]           2 u  135  256  337    0.004   
> -0.490   0.440
> -[name]          .GPS.            1 u  997 1024  377   88.936    
> 0.153   1.854
> +[name]          .GPS.            1 u  603 1024  377   88.146    
> 0.546   0.119
> *[name]          .GPS.            1 u  764 1024  377   88.311    
> 0.605   1.387
> -[name]          .GPS.            1 u  783 1024  377   73.649    
> 0.766  12.499
> #[name]          [name]           2 u  652 1024  377   83.509   
> -0.371   0.725
> -[name]          .GPS.            1 u  720 1024  377   32.581    
> 1.203   0.082
> +[name]          .GPS.            1 u  744 1024  377  105.719    
> 0.604   1.952
> -[name]          .GPS.            1 u  686 1024  377   92.301    
> 3.050   0.447
> #[name]          [name]           2 u  339 1024  176    0.796   
> -1.401   0.245
> #[name]          [name]           2 u  520 1024  376   10.376   
> -2.257   0.814
>  [name]          0.0.0.0         16 u    - 1024    0    0.000    0.000 
> 4000.00
>
> # time ntpd -gq [above 14 servers/peers with iburst, plus local. No 
> authentication.
>                  Default min/max poll. All appropriate for long-term time
>                  maintenance.]
> ntpd: time slew 0.000527s
>
> real    0m45.00s
> user    0m0.11s
> sys     0m0.55s
>
> [Note that ntpd -gq isn't really done when it unblocks. It has only
>  initiated a slew. But we'll let that pass becasuse the time is
>  already way more than "good enough".]
>
> # ntpdate -b [same set of servers and peers, except no local clock. Way
>               overconfigured for one-time "good enough" acquisition at 
> boot.]
>  4 Feb 13:21:32 ntpdate[201766]: step time server [IP] offset 0.000647 
> sec
>
> real    0m6.73s
> user    0m0.00s
> sys     0m0.00s
>
> ________________________________________________________________________
> Tom Smith                       smith at alum.mit.edu,smith at cag.lkg.hp.com
> Hewlett-Packard Company                          Tel: +1 (603) 884-6329
> 110 Spit Brook Road ZKO1-3/H42                   FAX: +1 (603) 884-6484
> Nashua, New Hampshire 03062-2698, USA           Mobile: +1 978 397 3411

If you omit the "q" option, ntpd will simply set the clock and keep 
running!  If the error is greater than 128 milliseconds it will step the 
clock, otherwise it will slew the clock.   In either case you are up and 
running with a clock error of less than 128 millieconds.  Is this not 
good enough?   If not, what is your requirement for accuracy?