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Re: Set your system clock



On Sunday 13 February 2005 17:36, Glenn English wrote:

> OTOH, I don't see any reason not to just turn off ntpd and let cron run
> ntpdate every hour or so (and at boot). That'd keep your clock accurate
> with less net bandwidth and resource usage.

Big reason #1: ntpdate is deprecated and may be removed at any point in the 
future - see http://www.ntp.org/ntpfaq/NTP-s-config.htm for details.

Big reason #2: ntpdate doesn't guarantee a monotonically increasing system 
time (translation: it may set the clock backwards).  Unix systems don't 
like that.

Big reason #3: ntpd only queries remote servers when it believes the local 
time might have drifted by more than an acceptable amount.  If you have a 
very stable clock, then it will ask for the time fairly rarely.  A cron job 
knows nothing about this: it asks once per configured time unit, whether 
the local clock is likely to be dead accurate or has already slipped far 
out of sync.

Big reason #4: if everyone put "0 * * * * ntpdate ntp.example.com" in their 
crontab, then once an hour ntp.example.com gets hammered.  This also means 
that those answers are likely to be far more delayed (and therefore 
inaccurate) then they are during the rest of the hour.  Besides, the 
ntp.example.com admins would hate you.

-- 
Kirk Strauser

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