[ntp:questions] New to NTP on Linux

Brad Knowles brad at stop.mail-abuse.org
Mon Oct 25 14:12:55 UTC 2004

At 5:53 AM -0700 2004-10-25, dusty bin wrote:

>  Presently running NTP on three W2K machines from 486 up to PII.
>  I want to add some refclocks using a) Garmin GPS25LVS and/or b)
>  Jonathan's MSF Rx.


>  Correct me if I am wrong, but this seems to imply running at least one
>  machine on Linux (of which my knowledge is minimal)...

	You can, but it's not strictly necessary.  I believe that the 
Windows port of the reference implementation will also support 
refclocks.  Of course, Windows has other problems with its clock, so 
you may very well be better off running another OS.

	Also note that some versions of Linux will require some kernel 
modifications to work well with NTP -- this is the PPSkit stuff. 
Then there are some other issues with Linux, but you'd have to see 
the archives of the comp.protocols.time.ntp newsgroup for more 
information on that.

	Note that FreeBSD supports NTP out-of-the-box without any kernel 
or userland modifications, and fully integrates the reference 
implementation.  If you use the latest version of FreeBSD, you will 
get ntpd 4.2.0, which is the current version of the reference 
implementation available via <http://ntp.isc.org/>.  If you run an 
earlier version of FreeBSD, you should be able to install the latest 
version of ntpd from the "ports" subsystem.

	If you're using an Intel box and looking for an alternative OS to 
run other than Windows, but which provides good support for NTP, my 
personal view is that FreeBSD is a better choice.  But that's only my 
personal view.

>  After a fair bit of faffing about, I now have Gentoo booting to the
>  commandline - so what next (I can't believe it would be as simple as
>  just doing #emerge ntp, etc.)?

	That would be a question you should probably ask on the mailing 
lists and newsgroups that are specific to your OS.

>  Q1. I realise that the Garmin isn't the best for the job, but it only
>  cost £11.50 - so it seemed worth a shot.  So, is the nanokernel patch
>  essential, or just 'nice-to-have' in order to have 1PPS?  Is it
>  irrelevant for a 486 installation?

	I don't think the Garmin is going to do very well in this job. 
It looks like it does include PPS and NMEA output, but I doubt that 
it's designed to provide good time sync.  Many GPS units will 
technically provide PPS and/or NMEA, but were designed to provide 
good positioning information as opposed to time.

	I believe that the Motorola Oncore is typically considered to be 
one of the best GPS units available for this function, but even there 
you have to take care to get the "+T" version, if you want to use it 
for NTP.  Specifically, you would want the Motorola Oncore M12+T.

	You might be able to use the Garmin for this function, but I 
would be surprised if it would work well.  Jonathan's MSF stuff may 
be a better option than the Garmin.

	Either way, I think you will definitely need the PPSKit mods.

	Now, with regards to the amount of CPU power needed for good 
operations, note that Poul-Henning Kamp has built some highly 
accurate clocks using Soekris single-board computers and Motorola 
Oncore GPS receivers, and the Soekris uses a chip that is essentially 
a 486.  So, you can get extremely accurate time from relatively 
low-powered systems, so long as you do the configuration correctly.

	See <http://phk.freebsd.dk/soekris/pps/> for more information, 
and Google for "PHK Soekris NTP" if you want to read various other 
related pages.

Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.

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