If you install the
tzdata source package, you will find all your answers:
sudo apt-get install apt-src
mkdir tzdata && cd tzdata
apt-src install tzdata
posix and right:
Two different versions are provided:
- The "posix" version is based on the Coordinated Universal Time (UTC).
- The "right" version is based on the International Atomic Time (TAI),
and it includes the leap seconds.
These entries are mostly present for historical reasons, so that
people in areas not otherwise covered by the tz files could "zic -l"
to a time zone that was right for their area. These days, the
tz files cover almost all the inhabited world, and the only practical
need now for the entries that are not on UTC are for ships at sea
that cannot use POSIX TZ settings.
GB, GB-Eire, GMT, GMT+0, GMT-0, GMT0, NZ, NZ-CHAT, PRC, ROC, ROK, UCT, UTC are there because the time zone names changed:
This file provides links between current names for time zones
and their old names. Many names changed in late 1993.
CET, CST6CDT, EET, EST, EST5EDT, HST, MET, MST, MST7MDT, PST8PDT, WET are there for backwards compatibility.
From Arthur David Olson, 2005-12-19
We generate the files specified below to guard against old files with
obsolete information being left in the time zone binary directory.
We limit the list to names that have appeared in previous versions of
this time zone package.
We do these as separate Zones rather than as Links to avoid problems if
a particular place changes whether it observes DST.
We put these specifications here in the northamerica file both to
increase the chances that they'll actually get compiled and to
avoid the need to duplicate the US rules in another file.