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It seems that CentOS does not have a ntp.drift or similar file. In /etc/ntp.conf, it says that you can use /var/lib/ntp/drift as a drift file but this file does not exist. Does CentOS does not consider drifting? Or does it let the user adjust if necessary? Or does it use another mechanism?

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Make sure ntpd can write to the directory. If so the file will be created see answer below. – Nils May 18 '12 at 20:04

If the drift file does not exist as ntpd starts, it enters a special mode designed to quickly adapt to the particular timing variances of the current hardware. This takes about 15 minutes, when ntpd begins to continuously track timing and frequency changes, relative to the current server. After an hour or so, ntpd writes the frequency drift factor to the configured drift file, which is then used at subsequent starts to allow ntpd to immediately enter its normal operational state. As it runs, ntpd writes timing information out to the drift file hourly.

So, a brief answer to your question would be "don't worry about it - ntpd should take care of it by itself, if the driftfile directive is specified in the config or on the command line."

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Also check that the /var/lib/ntp directory (and drift file if it exists) is owned by ntp and has the correct write permisions. I haven't seen this in a while, but...

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