[nSLUG] Clock drifts badly even when machine is up

Mike Spencer mspencer at tallships.ca
Sat Jul 2 04:14:08 ADT 2016


I noticed that my computer clock was off by a large amount so I
replaced the button battery. (Box is shut- & powered-down at night.)

Since then, I've checked against time.nrc.ca and found recurring
excursions.

Today, for example:

    root# date && ntpdate time.nrc.ca && date
    
    Fri Jul  1 15:16:55 ADT 2016
    1 Jul 15:16:59 ntpdate[5016]: adjust time server 132.246.11.229
                    offset 0.259334 sec
    Fri Jul  1 15:16:59 ADT 2016
    ---

    root# date && ntpdate time.nrc.ca && date

    Fri Jul  1 21:19:48 ADT 2016
    1 Jul 21:19:51 ntpdate[10317]: step time server 132.246.11.229 
                offset0.727260 sec
    Fri Jul  1 21:19:51 ADT 2016
    ---

    root# date && ntpdate time.nrc.ca && date

    Sat Jul  2 02:57:48 ADT 2016
    2 Jul 03:11:29 ntpdate[14942]: step time server 132.246.11.229 
                   offset 819.078979 sec
    Sat Jul  2 03:11:29 ADT 2016
    ---

So, roughly:

     4  sec drift since yesterday, down over night
     3  sec drift between 15:16 & 21:19 (~6 hrs)
     13 min drift between 21:19 & 03:11 (~6 hrs)
     
I played a DVD movie around midnight.  Is there any known problem with
mplayer or video interfering with the kernel's clock management?
Allegedly, mplayer consults the RTC but AIUI, the kernel is supposed to
consult the RTC only at boot

Any other suggestions about why this might be happening?

No, I haven't done exhaustive testing; hoping there's a "well-known"
answer.

Yes, I set up ntpd but I don't understand it.  The documentation
doesn't offer simple configs for simple scenarios -- "keep my one
computer up to date" -- and I have the additional problem that I'm on
dialup.  So I set up /etc/ppp/ip-{up,down} scripts to start
/etc/rc.d.rc.ntpd and the stop it. But I don't really know how to tell
if it's working.  Packets are exchanged every few minutes.  But I
disabled that last night to see if the problem recurred.  It has and
13 min is not "just a tad of drift".

In any case, the big excursion -- 13 min -- seems to have happened
while I was off-line.

Any suggestions?


- Mike

-- 
Michael Spencer                  Nova Scotia, Canada       .~. 
                                                           /V\ 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^




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