Subject: Re: rc.d: time synchronization issues at boot time
To: None <>
From: Alan Barrett <>
List: tech-userlevel
Date: 03/16/2005 17:35:34
On Wed, 16 Mar 2005, Luke Mewburn wrote:
> Does named need "good" time before it starts?

The signatures and keys used for DNS security contain expiry times,
validity periods, and such stuff.  Absolute time errors of a few seconds
will probably be fine; time errors of several minutes will probably not
be fine.  For example, see RFC 2845, which suggests a fudge factor of
300 seconds to accommodate clock skew between client and server, but the
actual fudge factor is up to the server or zone administrator, and parts
of DNSEC other than TSIG will have their own (different) requirements.

Time steps while named is running will interfere with named's cacheing
strategy, causing records to be cached for too long or too short a time
before expiring.  Here, errors of even a few minutes are likely to be
fine.  (Records that expire too soon can easily be retrieved again, and
records that expire a few minutes too late are unlikely to cause much

> Finally, what other `early' services should have "good time"
> (i.e, ntpdate) at boot ?

I suspect that kerberised NFS needs moderately accurate time.

Apart from anything else, it's nice if log messages are as accurate as
possible, which implies running ntpdate as early as possible.

--apb (Alan Barrett)