[LEAPSECS] POSIX Time (was WP7A)

[Joe Gwinn]

At 3:28 PM +0200 10/10/09, Magnus Danielson wrote:

>M. Warner Losh wrote:

>>In message: <4ACFF759.3090903 at rubidium.dyndns.org>

>>             Magnus Danielson <magnus at rubidium.dyndns.org> writes:

>>: M. Warner Losh wrote:

>>: > In message: 

>><13205C286662DE4387D9AF3AC30EF456AFA8697A05 at EMBX01-WF.jnpr.net>

>>: >             Jonathan Natale <jnatale at juniper.net> writes:

>>: > : AFAIK, routers also just re-sych.  The OS's are not capable of

>>: > : xx:xx:60 time.  For reading router logs this is fine in most cases

>>: > : which is all NTP is really for.  I don't think they simply step the

>>: > : time, I am pretty sure they do tweak the freq.  I could be wrong and

>>: > : I am NOT representing Juniper here, just my thoughts. :-)

>>: > : > FreeBSD will cope with the xx:xx:60 second correctly, assuming it is

>>: > told about the leapsecond soon enough.  Not all other parts of the

>>: > system can cope with the xx:xx:60, but that's a posix time_t

>>: > limitation that you can't do anything about[*].

>>: > : > Warner

>>: > : > [*] The 'right' timezone files attempt to do things correctly, but in

>>: > doing so they break time_t definition...

>>: : I assumed you meant to say that it breaks the POSIX time_t definition.

>>

>>Yes.  The most current time_t definition is the one codified by POSIX.

>>Older standards are fuzzier about what time_t really means.

>

>Indeed. As there exist several time_t definitions, I wanted to make 

>sure you was refering to the POSIX mapping of UTC time into time_t, 

>which forms an "interesting" timescale of its own, almost but not 

>close enough to UTC.


By definition, POSIX Time is closer to TAI than to UTC, but in 
practice time in POSIX-compliant computers is usually NTP steered to 
approximate UTC (most common) or to GPS System Time (where 
leapseconds cannot be tolerated).

Joe Gwinn