[ntp:questions] ntpd, boot time, and hot plugging
brad at stop.mail-abuse.org
Wed Feb 9 16:52:50 UTC 2005
At 2:05 PM -0200 2005-02-09, Alain wrote:
> Putting it in another way: If I configure a workstation with
> - ntpd -g
> - delete dift file only it it is +-500
> - no ntpdate
> then the clock will be right even if the clock battery is flat and then
> ntpd will go on keeping the clock in synch?
Note that the clock does have to be set within 34 years of the
real value on bootup. Otherwise, when ntpd sets the clock, there
will be an overflow condition and ntpd won't be able to detect that
it has set the clock to a wildly incorrect value. Many Unix systems
today, if they are booted after a BIOS battery failure, will come up
with a system clock that has been reset to some time in 1968, 1969,
or 1970. This is now more than 34 years ago, so you will need to
make sure that you take appropriate measures under these
Also note that if your system clock goes whacko after the initial
startup, ntpd may choose to commit suicide and exit, and there's
nothing you can do to stop that. Exiting when faced with totally
outrageous conditions is a perfectly normal state of affairs with
Unix-type daemons, and you need to be prepared to monitor the
existence of any critical programs on the system to make sure that
they're running correctly. This is true for ntpd, any other critical
program running on the system.
Depending on how you have constructed your /etc/ntp.conf file, it
may take a little while longer to complete the initialization
process. However, those two caveats aside, what you have said is
> Even if some messages with the wrong time manage to get to the log before
> the clock is corrected, this can be acceptable for a workstation. I will
> just have to figure out how to issue a warning message.
That's a normal state of affairs.
> What happen if I set the sanity limit to 0?
That's what "-g" does. But it does this only once, on startup.
After that, you're on your own.
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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