ntpd problem freebsd 5.3 [ and Re: I found your question about NTPd on Sep 27]

[Christian Hiris]

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On Monday 22 November 2004 03:40, animecowboy at animecowboy.com wrote:
> I am having the same problem you mentioned here.
> http://lists.freebsd.org/pipermail/freebsd-questions/2004-September/059279.
> html
>
> I was wondering if you ever found out the cause and/or a way to correct the
> problem.

As this answer appears to be more complete, than my first one, I attached it 
to the original thread, just for the archives. I'm not a ntp specialist, so 
maybe there are some things that I misunderstood, but I think it's better 
than no answer. ;-)

> Sep 23 17:13:41 panther ntpd[467]: kernel time sync enabled 2001
> Sep 23 21:29:44 panther ntpd[467]: kernel time sync enabled 6001
> Sep 23 21:46:48 panther ntpd[467]: kernel time sync enabled 2001
> Sep 24 01:11:39 panther ntpd[467]: kernel time sync enabled 6001
> Sep 24 01:45:47 panther ntpd[467]: kernel time sync enabled 2001
> Sep 24 02:19:59 panther ntpd[467]: kernel time sync enabled 6001

IMHO this isn't a problem - the messages are informational. ntpd just switches 
(kernel) clock discipline modes between PLL (Phase-Locked-Loop) and FLL 
(Frequency-Locked-Loop).

I recently found a good documentation on ntpd PLL/FLL hybrid mode (including 
the differences between ntp v3/v4 PLL/FLL mode's handling):   
http://www.eecis.udel.edu/~mills/database/papers/allan.pdf

I was pointed to the above link by  
http://www.freebsd.org/cgi/cvsweb.cgi/~checkout~/src/contrib/ntp/html/kern.html
You also can find this document in /usr/src, if you have sources installed on 
your system.

As I mentioned, there seems to be nothing wrong with messages 6001 and 2001.  
Kernel time discipline (and probably kernel time discipline messages) could 
be disabled via ntpdc control message's or ntpd config-file's "disable 
kernel" option. I think this also would disable nano-second 
clock-disciplining ability, so I would left it enabled. I never tried to 
disable kernel time discipline, so I can't imagine what would happen in real 
life ... 
http://www.freebsd.org/cgi/cvsweb.cgi/~checkout~/src/contrib/ntp/html/miscopt.html

See also the option "tinker allan" option. This option allows you to change 
the seconds for minimum Allan intercept, which is a parameter of the PLL/FLL 
clock discipline algorithm. I left this at default value, too.
http://www.freebsd.org/cgi/cvsweb.cgi/~checkout~/src/contrib/ntp/html/miscopt.html

Loopfilter's implementation can be found at: 
http://www.freebsd.org/cgi/cvsweb.cgi/~checkout~/src/contrib/ntp/ntpd/ntp_loopfilter.c
http://www.freebsd.org/cgi/cvsweb.cgi/~checkout~/src/sys/sys/timex.h


Two simple examples of ntpd status decoding (see timex.h):

Status message "time sync enabled 2001" tells us:

STA_PLL   0x0001  [true]   /* enable PLL updates (rw) */
STA_NANO  0x2000  [true]   /* resolution (0 = us, 1 = ns) (ro) */
STA_MODE  0x4000  [false]  /* mode (0 = PLL, 1 = FLL) (ro) *
STA_CLK   0x8000  [false]  /* clock source (0 = A, 1 = B) (ro) */
- ------------------------------------------------------------------
          0x2001  PLL upd. on, Resolution=ns, mode=PLL, clock-src=A    

Status message "time sync enabled 6001" tells us:

STA_PLL   0x0001  [true]   /* enable PLL updates (rw) */
STA_NANO  0x2000  [true]   /* resolution (0 = us, 1 = ns) (ro) */
STA_MODE  0x4000  [true]   /* mode (0 = PLL, 1 = FLL) (ro) *
STA_CLK   0x8000  [false]  /* clock source (0 = A, 1 = B) (ro) */
- -----------------------------------------------------------------
          0x6001  PLL upd. on, Resolution=ns, mode=FLL, clock-src=A    

Cheers,
ch

- -- 
Christian Hiris <4711 at chello.at> | OpenPGP KeyID 0x3BCA53BE 
OpenPGP-Key at hkp://wwwkeys.eu.pgp.net and http://pgp.mit.edu
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