[ntp:questions] ntpd sets clock to the year 1939

Richard B. gilbert rgilbert88 at comcast.net
Tue Mar 27 12:17:49 UTC 2007

David J Taylor wrote:
> Richard B. gilbert wrote:
> []
>>It's hardly ever a problem since most systems have a hardware clock of
>>some sort that can supply a reasonable starting point.  In 2007, I
>>don't think that 1970-is a reasonable starting point.
> Whilst I have some sympathy for that viewpoint, NTP should not today have 
> that 30-year limitation (delighted to hear it is being extended).
> It is not a defect of the OS that it allows its real-time clock to be set 
> /before/ the base time - 1970?
> David 

The "30-year" limitation is really, I believe, 36 years.  It's a 
artifact of the data structures used by the current implementation; a 
sixty-four bit word with the binary point in the middle is used to 
represent the seconds and fractional seconds since 1-JAN-1970.  This has 
served us well for the last 20 years or so.  I believe that the new 
standard is going to call for a 128 bit word which should last a few 
years longer. :-)

The fault, if any, is the way Unix keeps time.  I believe it's a signed 
32 bit integer keeping seconds since 1-JAN-1970.  Digital's VMS used a 
scheme  that could represent any time from a base time in November 1857 
through the next 30,000 years or so.  Unix time, at least until 
recently, would overflow in 2036.

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