The Time Zone Database (often called tz, tzdb, or zoneinfo) contains
data that represents the history of local time for many locations around
the world, and supports conversion of UTC time to local time at those
locations to allow display of those local times.
It is updated periodically to reflect changes made by political bodies to
summer daylight saving time rules, UTC offsets, and time zone boundaries.
Three data packages are available: base 'tzdata' is always installed;
optional 'tzdata-right' provides TAI-10s time in the 'right' subtree;
and optional 'tzdata-posix' provides the same zones and times as base
data in the 'posix' subtree, as an explicit distinction from 'right'.
To enable newlib CLOCK_TAI support, the base tzdata package now installs:
/usr/share/zoneinfo/leap-seconds.list
with a symbolic link from the standard location:
/etc/leap-seconds.list.
The tzcode package provides the tzselect, zdump, and zic utilities.
For more information, see the project home page:
https://www.iana.org/time-zones
The following packages have been upgraded in the Cygwin distribution:
- tzcode 2026d library and utilities
- tzdata 2026d base zones tree
- tzdata-posix 2026d posix zones subtree
- tzdata-right 2026d TAI-10s right zones subtree
For more details on changes, see the announcement or below:
https://lists.iana.org/hyperkitty/list/[email protected]/2026/09/
2026-09-11 2026d
Briefly:
- Canada's Northwest Territories moved to permanent -06 on 2026-08-21.
- Obsolescent settings like TZ="EST5EDT" now conform better to POSIX.
- Fix security, performance and porting bugs in zic and localtime.
Changes to future timestamps
- Canada's Northwest Territories will not fall back on 2026-11-01 and
will stay on -06 year-round, matching Alberta's recent change.
Model this with its traditional abbreviation CST.
Although the change to permanent -06 legally took place on 2026-08-21,
temporarily model the change to occur on 2026-11-01 at 02:00 for the
same reason as other recent temporary hacks.
(Caution: see âNOTE FOR 2026b TEMPORARY HACK FOR CLDR AND CANADAâ below.)
This affects only America/Inuvik as the rest of the territory is
covered by America/Edmonton, for which the equivalent change was
released in 2026c.
Changes to past timestamps
- Colombia's 1992-05-02 spring forward was at 00:00, not 24:00.
- Iran's 1979-05-26 spring forward was at 00:00, not 24:00.
- The backward-compatibility names EST5EDT, CST6CDT, MST7MDT, and
PST8PDT now conform better to POSIX.
For example, EST5EDT now always uses the abbreviation "EST" for
standard time (now always 5 hours behind UT) and "EDT" for daylight
saving time, whereas it formerly had different UT offsets before
standard time was introduced and sometimes used abbreviations like
"LMT", "EWT" and "EPT", all contrary to POSIX.
Also, though not required by POSIX these names now use US federal
rules rather than rules of places like New York, reverting to 2024a
behavior.
This change affects only timestamps before 1966-10-30 at 01:00
standard time.
Other data changes
- The temporary hacks used for North American timekeeping changes now
work around a libstdc++ std::chrono bug in GCC 14.1-14.4, 15.1-15.2,
and 16.1; see GCC bug 124851.
This data change does not affect TZif files or timestamps.
The change does not work around the related but less serious GCC bugs
116110 and 124513.
These GCC bugs are all fixed in GCC 16.2.
Changes to code
- zic now rejects Link targets that would have invalid names, and more
efficiently processes Expires, Leap and Rule lines with years far in
the past or future.
- zic now ports to systems that report lack of link support via EINVAL,
ENOSYS or EPERM errno values.
- When tzset and related functions encounter a TZif file that is too
large for them, they now consistently fail instead of sometimes
silently ignoring excess parts of the file.
- localtime-related functions no longer mishandle extreme timestamps
when given TZif files holding some unlikely timezone histories.
- localtime-related functions no longer check the values of TZif files'
standard/wall and UT/local indicators, which these functions have not
used since 2026a's removal of the old posixrules feature.
- tzcode has been ported to Haiku.
- localtime.c now works again by default on AIX and DragonFly BSD.
- zic now rejects ':' and '\' in Zone and Link names when running on
Microsoft Windows.
Changes to documentation
- URLs for release tarballs in tz-link.html have been updated to reflect
their new canonical URLs on data.iana.org.
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