Use of GMT in BSD

tuco at
Sun Apr 13 02:03:32 PDT 2003


I see GMT being used in FreeBSD and wonder why an old astronomical time scale 
that has been obsolete for a long time now as the basis for the World's civil 
time is still used?
That is, Coordinated Universal Time (UTC), the basis for all civil time, 
superseded GMT when the world converted to an atomic time scale and is also 
an internationally agreed upon time scale-- even in the UK.  I know GMT is 
steeped in tradition and has meant a different time to different people in 
the past but it is not technically correct to say GMT because it really means 
UTC when you say it.  No master clock measures GMT anymore because these 
clocks are atomic clock measuring International Atomic Time (TAI) and UTC is 
derived from TAI. 

To the resolution of a stratum 2, NTP time server you can run on FreeBSD, GMT 
and UTC are different times. In fract, the time your stratum 2 server gets 
from the stratum 1 servers is UTC.  Identifying your time scale is similar to 
identifying your units in, say, a measurement of length.  

Thanx for your attention
Seattle, WA

Explanatory Supplement to the Astronomical Almanac, U.S Naval Observatory,       
Chapter 2 - Time. 1992. -- Notice the absence of GMT here -- One agency that maintains the time standard. 
Note the absence of GMT. -- Definitions of the many time 
scales.  Note the absence of GMT.

NBS Frequency and Time Broadcast Services, Radio Stations WWV, WWVH, WWVB, 
Special Publication 236, 1972 Edition.  ( yes,that long ago)

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