[ntp:questions] Correcting a large time difference

David Woolley david at ex.djwhome.demon.invalid
Sat Jul 31 09:08:00 UTC 2010

Richard Heritage wrote:
> I've inherited a RHEL 5 server that isn't running ntp and whose clock
is about 30 minutes fast. What I would like to do is start ntpd & have
it gradually correct the clock. I don't care how long it takes--it's
been running this way for months. The server runs an email application
that may be sensitive to a large backward jump in the clock, and leaving
the server down for a half hour isn't a good option.

Do not run ntpd. Use ntptime to set the tickadj value to give the 
highest acceptable slew rate (granularity is typically 100ppm).  Reset 
it to normal as you approach the zero crossing.  Measure the residual 
frequency error and calculate the ntp.drift value for it.  Set that 
value in ntp.drift and start ntpd.

ntptime goes by other names on some systems.

PS Please don't write your paragraphs all on one line.  There are proper 
ways of representing wrapped text in MIME email.

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