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Diffstat (limited to 'etc/ntp/leap-seconds')
| -rw-r--r-- | etc/ntp/leap-seconds | 221 |
1 files changed, 221 insertions, 0 deletions
diff --git a/etc/ntp/leap-seconds b/etc/ntp/leap-seconds new file mode 100644 index 0000000..8fa6225 --- /dev/null +++ b/etc/ntp/leap-seconds @@ -0,0 +1,221 @@ +# +# $FreeBSD$ +# +# In the following text, the symbol '#' introduces +# a comment, which continues from that symbol until +# the end of the line. A plain comment line has a +# whitespace character following the comment indicator. +# There are also special comment lines defined below. +# A special comment will always have a non-whitespace +# character in column 2. +# +# A blank line should be ignored. +# +# The following table shows the corrections that must +# be applied to compute International Atomic Time (TAI) +# from the Coordinated Universal Time (UTC) values that +# are transmitted by almost all time services. +# +# The first column shows an epoch as a number of seconds +# since 1900.0 and the second column shows the number of +# seconds that must be added to UTC to compute TAI for +# any timestamp at or after that epoch. The value on +# each line is valid from the indicated initial instant +# until the epoch given on the next one or indefinitely +# into the future if there is no next line. +# (The comment on each line shows the representation of +# the corresponding initial epoch in the usual +# day-month-year format. The epoch always begins at +# 00:00:00 UTC on the indicated day. See Note 5 below.) +# +# Important notes: +# +# 1. Coordinated Universal Time (UTC) is often referred to +# as Greenwich Mean Time (GMT). The GMT time scale is no +# longer used, and the use of GMT to designate UTC is +# discouraged. +# +# 2. The UTC time scale is realized by many national +# laboratories and timing centers. Each laboratory +# identifies its realization with its name: Thus +# UTC(NIST), UTC(USNO), etc. The differences among +# these different realizations are typically on the +# order of a few nanoseconds (i.e., 0.000 000 00x s) +# and can be ignored for many purposes. These differences +# are tabulated in Circular T, which is published monthly +# by the International Bureau of Weights and Measures +# (BIPM). See www.bipm.fr for more information. +# +# 3. The current defintion of the relationship between UTC +# and TAI dates from 1 January 1972. A number of different +# time scales were in use before than epoch, and it can be +# quite difficult to compute precise timestamps and time +# intervals in those "prehistoric" days. For more information, +# consult: +# +# The Explanatory Supplement to the Astronomical +# Ephemeris. +# or +# Terry Quinn, "The BIPM and the Accurate Measurement +# of Time," Proc. of the IEEE, Vol. 79, pp. 894-905, +# July, 1991. +# +# 4. The insertion of leap seconds into UTC is currently the +# responsibility of the International Earth Rotation Service, +# which is located at the Paris Observatory: +# +# Central Bureau of IERS +# 61, Avenue de l'Observatoire +# 75014 Paris, France. +# +# Leap seconds are announced by the IERS in its Bulletin C +# +# See hpiers.obspm.fr or www.iers.org for more details. +# +# All national laboratories and timing centers use the +# data from the BIPM and the IERS to construct their +# local realizations of UTC. +# +# Although the definition also includes the possibility +# of dropping seconds ("negative" leap seconds), this has +# never been done and is unlikely to be necessary in the +# foreseeable future. +# +# 5. If your system keeps time as the number of seconds since +# some epoch (e.g., NTP timestamps), then the algorithm for +# assigning a UTC time stamp to an event that happens during a positive +# leap second is not well defined. The official name of that leap +# second is 23:59:60, but there is no way of representing that time +# in these systems. +# Many systems of this type effectively stop the system clock for +# one second during the leap second and use a time that is equivalent +# to 23:59:59 UTC twice. For these systems, the corresponding TAI +# timestamp would be obtained by advancing to the next entry in the +# following table when the time equivalent to 23:59:59 UTC +# is used for the second time. Thus the leap second which +# occurred on 30 June 1972 at 23:59:59 UTC would have TAI +# timestamps computed as follows: +# +# ... +# 30 June 1972 23:59:59 (2287785599, first time): TAI= UTC + 10 seconds +# 30 June 1972 23:59:60 (2287785599,second time): TAI= UTC + 11 seconds +# 1 July 1972 00:00:00 (2287785600) TAI= UTC + 11 seconds +# ... +# +# If your system realizes the leap second by repeating 00:00:00 UTC twice +# (this is possible but not usual), then the advance to the next entry +# in the table must occur the second time that a time equivlent to +# 00:00:00 UTC is used. Thus, using the same example as above: +# +# ... +# 30 June 1972 23:59:59 (2287785599): TAI= UTC + 10 seconds +# 30 June 1972 23:59:60 (2287785600, first time): TAI= UTC + 10 seconds +# 1 July 1972 00:00:00 (2287785600,second time): TAI= UTC + 11 seconds +# ... +# +# in both cases the use of timestamps based on TAI produces a smooth +# time scale with no discontinuity in the time interval. +# +# This complexity would not be needed for negative leap seconds (if they +# are ever used). The UTC time would skip 23:59:59 and advance from +# 23:59:58 to 00:00:00 in that case. The TAI offset would decrease by +# 1 second at the same instant. This is a much easier situation to deal +# with, since the difficulty of unambiguously representing the epoch +# during the leap second does not arise. +# +# Questions or comments to: +# Jeff Prillaman +# Time Service Department +# US Naval Observatory +# Washington, DC +# jeffrey.prillaman@usno.navy.mil +# +# Last Update of leap second values: 31 Dec 2015 +# +# The following line shows this last update date in NTP timestamp +# format. This is the date on which the most recent change to +# the leap second data was added to the file. This line can +# be identified by the unique pair of characters in the first two +# columns as shown below. +# +#$ 3660508800 +# +# The data in this file will be updated periodically as new leap +# seconds are announced. In addition to being entered on the line +# above, the update time (in NTP format) will be added to the basic +# file name leap-seconds to form the name leap-seconds.<NTP TIME>. +# In addition, the generic name leap-seconds.list will always point to +# the most recent version of the file. +# +# This update procedure will be performed only when a new leap second +# is announced. +# +# The following entry specifies the expiration date of the data +# in this file in units of seconds since 1900.0. This expiration date +# will be changed at least twice per year whether or not a new leap +# second is announced. These semi-annual changes will be made no +# later than 1 June and 1 December of each year to indicate what +# action (if any) is to be taken on 30 June and 31 December, +# respectively. (These are the customary effective dates for new +# leap seconds.) This expiration date will be identified by a +# unique pair of characters in columns 1 and 2 as shown below. +# In the unlikely event that a leap second is announced with an +# effective date other than 30 June or 31 December, then this +# file will be edited to include that leap second as soon as it is +# announced or at least one month before the effective date +# (whichever is later). +# If an announcement by the IERS specifies that no leap second is +# scheduled, then only the expiration date of the file will +# be advanced to show that the information in the file is still +# current -- the update time stamp, the data and the name of the file +# will not change. +# +# Updated through IERS Bulletin C 50 +# File expires on: 1 Jun 2016 +# +#@ 3673728000 +# +2272060800 10 # 1 Jan 1972 +2287785600 11 # 1 Jul 1972 +2303683200 12 # 1 Jan 1973 +2335219200 13 # 1 Jan 1974 +2366755200 14 # 1 Jan 1975 +2398291200 15 # 1 Jan 1976 +2429913600 16 # 1 Jan 1977 +2461449600 17 # 1 Jan 1978 +2492985600 18 # 1 Jan 1979 +2524521600 19 # 1 Jan 1980 +2571782400 20 # 1 Jul 1981 +2603318400 21 # 1 Jul 1982 +2634854400 22 # 1 Jul 1983 +2698012800 23 # 1 Jul 1985 +2776982400 24 # 1 Jan 1988 +2840140800 25 # 1 Jan 1990 +2871676800 26 # 1 Jan 1991 +2918937600 27 # 1 Jul 1992 +2950473600 28 # 1 Jul 1993 +2982009600 29 # 1 Jul 1994 +3029443200 30 # 1 Jan 1996 +3076704000 31 # 1 Jul 1997 +3124137600 32 # 1 Jan 1999 +3345062400 33 # 1 Jan 2006 +3439756800 34 # 1 Jan 2009 +3550089600 35 # 1 Jul 2012 +3644697600 36 # 1 Jul 2015 +# +# the following special comment contains the +# hash value of the data in this file computed +# use the secure hash algorithm as specified +# by FIPS 180-1. See the files in ~/sha for +# the details of how this hash value is +# computed. Note that the hash computation +# ignores comments and whitespace characters +# in data lines. It includes the NTP values +# of both the last modification time and the +# expiration time of the file, but not the +# white space on those lines. +# the hash line is also ignored in the +# computation. +# +#h 44a44c49 35b22601 a9c7054c 8c56cf57 9b6f6ed5 +# |
