F-ckin Leap Seconds, how do they work?

Thu Jul 5 15:29:11 UTC 2012

On Jul 5, 2012, at 10:49 48AM, Peter Lothberg wrote:

>>> On one of my BSD boxes. /usr/src/share/zoneinfo/leapseconds, I see no
>>> "-"
>> No, but they're allowed; see Figure 9 of RFC 5905:
> 
> Steve, 
> 
> I commented that it was stated that we where doing both positive and
> negative corrections. Only positive corrections have been made, and
> yes, negative are possible. 
> 
> I pointed out in a previous post that we can count 57, 58, 00 
> or 57, 58, 59, 00 or 57, 58, 59, 60, 00. And actually, this is the
> only thing operating-systems and applications need to be capable to
> handle to make it a non_issue. 

Fair enough.

> 
> 
>>   LI Leap Indicator (leap): 2-bit integer warning of an impending leap
>>   second to be inserted or deleted in the last minute of the current
>>   month with values defined in Figure 9.
>> 
>>           +-------+----------------------------------------+
>>           | Value | Meaning                                |
>>           +-------+----------------------------------------+
>>           | 0     | no warning                             |
>>           | 1     | last minute of the day has 61 seconds  |
>>           | 2     | last minute of the day has 59 seconds  |
>>           | 3     | unknown (clock unsynchronized)         |
>>           +-------+----------------------------------------+
> 
> That's NTP packet format, used to implemment NTP's represenation of
> UTC, but not the definition of UTC... (What do I do if I receive a
> packet with "3".) Or better, all the UTC(k) are free-running and the
> (old) recomenadtion was to try to keep them within 1us, is that
> unsyncronized -:)
> 
> And ooops, I did not catch that before, should it not say "last minute
> of the month"?  

The text as I copied it is certainly not consistent...

> 
> If I remember right the posix standard don't allow "60" in seconds...
> 
> -Peter
> 

		--Steve Bellovin, https://www.cs.columbia.edu/~smb