Re: How to use ntp/ntpdate to fix my clock
On Tue, 15 Feb 2000, Patrick Dahiroc wrote:
>already on Feb 15, 2000. digging through the package database i came across
>ntp and ntpdate and installed both (i have an always on connection to the
ntpdate is used to do a "one time only" update to your clock. ntp is used to
discipline your clock and will in fact keep the RTC in a short leash
updating it every 11 minutes.
If you're going to use ntp (not ntpdate), remember to get rid of that
systohc adjust crap in runlevel 6 (/etc/rc6.d, /etc/init.d; I forgot the
script name, I think a search for systohc --adjust will find it). It does
not play well with ntp most of the time.
If you use ntp, you must use ntpdate as well. Ntp will refuse to run if your
clock is off by more than a certain amount of time (which isn't very big
BTW, so this is a real risk). ntpdate is used to 'force' the clock to an
acceptable value at boot time, and after that you can either leave the RTC
alone or use ntp to keep it synced.
Ntp *requires* a reliable, fast, permanent internet connection for at least
four or five hours a day to work properly AFAIK (but it really wants 24/7
connections), as well as a good configuration and nearby stratum2 time
servers (it will work otherwise, yes. But not properly and you'd be better
off with only ntpdate).
If you don't have such a connection, restrain yourself to ntpdate. If you
use modems for dialup, forget ntp and use ntpdate. If you don't have the
time to read http://www.ntp.org/ and the docs in the package ntp-doc (which
you didn't read or you'd not be asking the ML), and search the stratum *2*
servers list for at least 2 near you (ping < 300ms is a must. <100ms is
desired), request permission to use them (ntp will keep hammering them every
64-1024s, unlike ntpdate which does it only once), and deal with the hassle,
you'd be better off with only ntpdate.
> specify a server to ask. is there a list of machine that listens for ntpdate
> connection? where? do i need to get permission (something to do with auth
There's a list in http://www.ntp.org. You want the stratum ->**2**<-
servers, not the Stratum 1 servers.
>stuff) to ask those machines for the time?
If you're using ntp, then YES, you must request permission to use the server
about 4 times out of 5. If you're using ntpdate you should ask first, but
since ntpdate only connects to the server when you run it (i.e.: once on
every reboot, most people add a cron job for once a day as well) you might
get away without asking permission.
My advice is to stick to ntpdate, it is MUCH easier to config :-)
--
"One disk to rule them all, One disk to find them. One disk to bring
them all and in the darkness grind them. In the Land of Redmond
where the shadows lie." -- The Silicon Valley Tarot
Henrique Holschuh
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