Date: Thu, 17 Nov 2005 07:30:06 +1300 From: Jonathan Chen <jonc@chen.org.nz> To: Chuck Swiger <cswiger@mac.com> Cc: "Andrew P." <infofarmer@gmail.com>, fbsdq <freebsd-questions@freebsd.org> Subject: Re: ntpdate Message-ID: <20051116183006.GB2539@osiris.chen.org.nz> In-Reply-To: <437B67D9.50108@mac.com> References: <20051115214101.fb30f4fa.dick@nagual.st> <OF05714E37.11452ACB-ONC22570BB.00538A7F-C22570BB.0053CF95@procreditbank.bg> <20051116162615.0a3b7707.dick@nagual.st> <cb5206420511160857v215f91fchb9650618baf903e8@mail.gmail.com> <437B67D9.50108@mac.com>
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On Wed, Nov 16, 2005 at 12:09:45PM -0500, Chuck Swiger wrote:
[...]
> Running "ntpdate -b" at boot to forcibly syncronize the clock is a pretty
> good idea, but you actually can convince ntpd to sync even a clock which is
> badly off via:
>
> -g Normally, ntpd exits if the offset exceeds the sanity limit,
> which is 1000 s by default. If the sanity limit is set to
> zero,
> no sanity checking is performed and any offset is acceptable.
> This option overrides the limit and allows the time to be set
> to
> any value without restriction; however, this can happen only
> once. After that, ntpd will exit if the limit is exceeded.
> This
> option can be used with the -q option.
The advantage of `ntpdate' vs `ntpd -g' is that ntpdate does it
_immediately_, whereas `ntpd -g' takes a bit of time before it decides
which server to sync to. This means that if your clock is out by
hours/days, there will be a period of 3-7 minutes after you boot where
your system time is badly incorrect, and then you have this big skip
when it corrects.
This could be a problem if you've got overanxious users running
`make' and other time sensitive programs almost immediately after boot;
not to mention weird skips in your various log files.
Cheers.
--
Jonathan Chen <jonc@chen.org.nz>
----------------------------------------------------------------------
"If everything's under control, you're going too slow"
- Mario Andretti
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