[TriLUG] ntpd misbehaving

[Glenn Hennessee]

PPM is most likely parts per million.
glenn

Michael Hrivnak wrote:
> I run ntpd on a Mandriva machine in my home and sync the rest of my machines 
> to it.  It keeps very good time, and according to ntpq, the offsets and 
> jitters relative to higher-stratum machines are quite low.
> 
> Then there's my desktop machine which has serious problems keeping time.  It 
> runs ntpd configured as so:
> 
> /*------------------
> #/etc/ntp.conf
> server 192.168.12.1 prefer maxpoll 7
> driftfile /etc/ntp/drift
> multicastclient                 # listen on default 224.0.1.1
> broadcastdelay  0.008
> -------------------*/
> 
> The clock tends to rapidly gain time.  24 hours after manually syncing the 
> time (ntpdate 192.168.12.1) and then starting ntpd, here's where it sat:
> 
> /*----------------
> # ntpq -p
>      remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
>  192.168.12.1    128.2.181.91     3 u   21  128  377    0.261  -101968 1243.16
> --------------------*/
> 
> Apparently it's exceeding the maximum tolerable drift value, as seen here in 
> the logs:
> 
> /*----------------
> # zgrep ntpd /var/log/syslog.*
> syslog.5.gz:Nov 20 02:03:54 localhost ntpd[3844]: synchronized to 
> 192.168.12.1, stratum=3
> syslog.5.gz:Nov 20 02:08:11 localhost ntpd[3844]: frequency error -512 PPM 
> exceeds tolerance 500 PPM
> syslog.5.gz:Nov 20 02:12:29 localhost ntpd[3844]: time reset -1.441427 s
> syslog.5.gz:Nov 20 02:12:29 localhost ntpd[3844]: frequency error -512 PPM 
> exceeds tolerance 500 PPM
> syslog.5.gz:Nov 20 02:22:09 localhost ntpd[3844]: synchronized to 
> 192.168.12.1, stratum=3
> syslog.5.gz:Nov 20 02:22:09 localhost ntpd[3844]: frequency error -512 PPM 
> exceeds tolerance 500 PPM
> syslog.5.gz:Nov 20 02:29:37 localhost ntpd[3844]: time reset -1.529274 s
> syslog.5.gz:Nov 20 02:29:37 localhost ntpd[3844]: frequency error -512 PPM 
> exceeds tolerance 500 PPM
> ----------------*/
> 
> There are several questions here.  Foremost, what can I do to keep better 
> time?  Other questions are: What exactly is "jitter"? I can't even find what 
> it's units are.  My understanding is that the frequency error is in 
> milliseconds, but what does PPM stand for?  Why won't it tolerate a greater 
> frequency error?
> 
> Thanks!
> 
> Michael