News for the tz database

Unreleased, experimental changes

Briefly:

Improve historical data for Mongolia, Portugal and possessions.

System V names are now obsolescent.

The main data form now uses %z.

The code now conforms to RFC 8536 for early timestamps.

Support POSIX.1-2024, which removes asctime_r and ctime_r.

Assume POSIX.2-1992 or later for shell scripts.

SUPPORT_C89 now defaults to 1.

Changes to past timestamps

Asia/Choibalsan is now an alias for Asia/Ulaanbaatar rather than

being a separate Zone with differing behavior before April 2008.

This seems better given our wildly conflicting information about

Mongolia's time zone history. (Thanks to Heitor David Pinto.)

Historical transitions for Portugal, represented by Europe/Lisbon,

Atlantic/Azores, and Atlantic/Madeira, have been updated based on a

close reading of old Portuguese legislation, replacing previous data

mainly originating from Whitman and Shanks & Pottenger. These

changes affect a few transitions in 1917-1921, 1924, and 1940

throughout these regions by a few hours or days, and various

timestamps between 1977 and 1993 depending on the region. In

particular, the Azores and Madeira did not observe DST from 1977 to

1981. Additionally, the adoption of standard zonal time in former

Portuguese colonies have been adjusted: Africa/Maputo in 1909, and

Asia/Dili by 22 minutes at the start of 1912.

(Thanks to Tim Parenti.)

Changes to past tm_isdst flags

The period from 1966-04-03 through 1966-10-02 in Portugal is now

modeled as DST, to more closely reflect how contemporaneous changes

in law entered into force.

Changes to data

Names present only for compatibility with UNIX System V

(last released in the 1990s) have been moved to 'backward'.

These names, which for post-1970 timestamps mostly just duplicate

data of geographical names, were confusing downstream uses.

Names moved to 'backward' are now links to geographical names.

This affects behavior for TZ='EET' for some pre-1981 timestamps,

for TZ='CET' for some pre-1947 timestamps, and for TZ='WET' for

some pre-1996 timestamps. Also, TZ='MET' now behaves like

TZ='CET' and so uses the abbreviation "CET" rather than "MET".

Those needing the previous TZDB behavior, which does not match any

real-world clocks, can find the old entries in 'backzone'.

(Problem reported by Justin Grant.)

The main source files' time zone abbreviations now use %z,

supported by zic since release 2015f and used in vanguard form

since release 2022b. For example, America/Sao_Paulo now contains

the zone continuation line "-3:00 Brazil %z", which is less error

prone than the old "-3:00 Brazil -03/-02". This does not change

the represented data: the generated TZif files are unchanged.

Rearguard form still avoids %z, to support obsolescent parsers.

Asia/Almaty has been removed from zonenow.tab as it now agrees

with Asia/Tashkent for future timestamps, due to Kazakhstan's

2024-02-29 time zone change. Similarly, America/Scoresbysund

has been removed, as it now agrees with America/Nuuk due to

its 2024-03-31 time zone change.

Changes to code

localtime.c now always uses a TZif file's time type 0 to handle

timestamps before the file's first transition. Formerly,

localtime.c sometimes inferred a different time type, in order to

handle problematic data generated by zic 2018e or earlier. As it

is now safe to assume more recent versions of zic, there is no

longer a pressing need to fail to conform RFC 8536 section 3.2,

which requires using time type 0 in this situation. This change

does not affect behavior when reading TZif files generated by zic

2018f and later.

POSIX.1-2024 removes asctime_r and ctime_r and does not let

libraries define them, so remove them except when needed to

conform to earlier POSIX. These functions are dangerous as they

can overrun user buffers. If you still need them, add

-DSUPPORT_POSIX2008 to CFLAGS.

The SUPPORT_C89 option now defaults to 1 instead of 0, fixing a

POSIX-conformance bug introduced in 2023a.

tzselect now supports POSIX.1-2024 proleptic TZ strings. Also, it

assumes POSIX.2-1992 or later, as practical porting targets now

all support that, and it uses some features from POSIX.1-2024 if

available.

Changes to build procedure

'make check' no longer requires curl and Internet access.

The build procedure now assumes POSIX.2-1992 or later, to simplify

maintenance. To build on Solaris 10, the only extant system still

defaulting to pre-POSIX, prepend /usr/xpg4/bin to PATH.

Changes to documentation

The documentation now reflects POSIX.1-2024.

Changes to commentary

Commentary about historical transitions in Portugal and her former

colonies has been expanded with links to many relevant legislation.

(Thanks to Tim Parenti.)

Release 2024a - 2024-02-01 09:28:56 -0800

Briefly:

Kazakhstan unifies on UTC+5 beginning 2024-03-01.

Palestine springs forward a week later after Ramadan.

zic no longer pretends to support indefinite-past DST.

localtime no longer mishandles Ciudad Juárez in 2422.

Changes to future timestamps

Kazakhstan unifies on UTC+5. This affects Asia/Almaty and

Asia/Qostanay which together represent the eastern portion of the

country that will transition from UTC+6 on 2024-03-01 at 00:00 to

join the western portion. (Thanks to Zhanbolat Raimbekov.)

Palestine springs forward a week later than previously predicted

in 2024 and 2025. (Thanks to Heba Hamad.) Change spring-forward

predictions to the second Saturday after Ramadan, not the first;

this also affects other predictions starting in 2039.

Changes to past timestamps

Asia/Ho_Chi_Minh's 1955-07-01 transition occurred at 01:00

not 00:00. (Thanks to Đoàn Trần Công Danh.)

From 1947 through 1949, Toronto's transitions occurred at 02:00

not 00:00. (Thanks to Chris Walton.)

In 1911 Miquelon adopted standard time on June 15, not May 15.

Changes to code

The FROM and TO columns of Rule lines can no longer be "minimum"

or an abbreviation of "minimum", because TZif files do not support

DST rules that extend into the indefinite past - although these

rules were supported when TZif files had only 32-bit data, this

stopped working when 64-bit TZif files were introduced in 1995.

This should not be a problem for realistic data, since DST was

first used in the 20th century. As a transition aid, FROM columns

like "minimum" are now diagnosed and then treated as if they were

the year 1900; this should suffice for TZif files on old systems

with only 32-bit time_t, and it is more compatible with bugs in

2023c-and-earlier localtime.c. (Problem reported by Yoshito

Umaoka.)

localtime and related functions no longer mishandle some

timestamps that occur about 400 years after a switch to a time

zone with a DST schedule. In 2023d data this problem was visible

for some timestamps in November 2422, November 2822, etc. in

America/Ciudad_Juarez. (Problem reported by Gilmore Davidson.)

strftime %s now uses tm_gmtoff if available. (Problem and draft

patch reported by Dag-Erling Smørgrav.)

Changes to build procedure

The leap-seconds.list file is now copied from the IERS instead of

from its downstream counterpart at NIST, as the IERS version is

now in the public domain too and tends to be more up-to-date.

(Thanks to Martin Burnicki for liaisoning with the IERS.)

Changes to documentation

The strftime man page documents which struct tm members affect

which conversion specs, and that tzset is called. (Problems

reported by Robert Elz and Steve Summit.)

Release 2023d - 2023-12-21 20:02:24 -0800

Briefly:

Ittoqqortoormiit, Greenland changes time zones on 2024-03-31.

Vostok, Antarctica changed time zones on 2023-12-18.

Casey, Antarctica changed time zones five times since 2020.

Code and data fixes for Palestine timestamps starting in 2072.

A new data file zonenow.tab for timestamps starting now.

Changes to future timestamps

Ittoqqortoormiit, Greenland (America/Scoresbysund) joins most of

the rest of Greenland's timekeeping practice on 2024-03-31, by

changing its time zone from -01/+00 to -02/-01 at the same moment

as the spring-forward transition. Its clocks will therefore not

spring forward as previously scheduled. The time zone change

reverts to its common practice before 1981.

Fix predictions for DST transitions in Palestine in 2072-2075,

correcting a typo introduced in 2023a.

Changes to past and future timestamps

Vostok, Antarctica changed to +05 on 2023-12-18. It had been at

+07 (not +06) for years. (Thanks to Zakhary V. Akulov.)

Change data for Casey, Antarctica to agree with timeanddate.com,

by adding five time zone changes since 2020. Casey is now at +08

instead of +11.

Changes to past tm_isdst flags

Much of Greenland, represented by America/Nuuk, changed its

standard time from -03 to -02 on 2023-03-25, not on 2023-10-28.

This does not affect UTC offsets, only the tm_isdst flag.

(Thanks to Thomas M. Steenholdt.)

New data file

A new data file zonenow.tab helps configure applications that use

timestamps dated from now on. This simplifies configuration,

since users choose from a smaller Zone set. The file's format is

experimental and subject to change.

Changes to code

localtime.c no longer mishandles TZif files that contain a single

transition into a DST regime. Previously, it incorrectly assumed

DST was in effect before the transition too. (Thanks to Alois

Treindl for debugging help.)

localtime.c's timeoff no longer collides with OpenBSD 7.4.

The C code now uses _Generic only if __STDC_VERSION__ says the

compiler is C11 or later.

tzselect now optionally reads zonenow.tab, to simplify when

configuring only for timestamps dated from now on.

tzselect no longer creates temporary files.

tzselect no longer mishandles the following:

Spaces and most other special characters in BUGEMAIL, PACKAGE,

TZDIR, and VERSION.

TZ strings when using mawk 1.4.3, which mishandles regular

expressions of the form /X{2,}/.

ISO 6709 coordinates when using an awk that lacks the GNU

extension of newlines in -v option-arguments.

Non UTF-8 locales when using an iconv command that lacks the GNU

//TRANSLIT extension.

zic no longer mishandles data for Palestine after the year 2075.

Previously, it incorrectly omitted post-2075 transitions that are

predicted for just before and just after Ramadan. (Thanks to Ken

Murchison for debugging help.)

zic now works again on Linux 2.6.16 and 2.6.17 (2006).

(Problem reported by Rune Torgersen.)

Changes to build procedure

The Makefile is now more compatible with POSIX:

* It no longer defines AR, CC, CFLAGS, LDFLAGS, and SHELL.

* It no longer uses its own 'cc' in place of CC.

* It now uses ARFLAGS, with default specified by POSIX.

* It does not use LFLAGS incompatibly with POSIX.

* It uses the special .POSIX target.

* It quotes special characters more carefully.

* It no longer mishandles builds in an ISO 8859 locale.

Due to the CC changes, TZDIR is now #defined in a file tzdir.h

built by 'make', not in a $(CC) -D option. Also, TZDEFAULT is

now treated like TZDIR as they have similar roles.

Changes to commentary

Limitations and hazards of the optional support for obsolescent

C89 platforms are documented better, along with a tentative

schedule for removing this support.

Release 2023c - 2023-03-28 12:42:14 -0700

Changes to past and future timestamps

Model Lebanon's DST chaos by reverting data to tzdb 2023a.

(Thanks to Rany Hany for the heads-up.)

Release 2023b - 2023-03-23 19:50:38 -0700

Changes to future timestamps

This year Lebanon springs forward April 20/21 not March 25/26.

(Thanks to Saadallah Itani.) [This was reverted in 2023c.]

Release 2023a - 2023-03-22 12:39:33 -0700

Briefly:

Egypt now uses DST again, from April through October.

This year Morocco springs forward April 23, not April 30.

Palestine delays the start of DST this year.

Much of Greenland still uses DST from 2024 on.

America/Yellowknife now links to America/Edmonton.

tzselect can now use current time to help infer timezone.

The code now defaults to C99 or later.

Fix use of C23 attributes.

Changes to future timestamps

Starting in 2023, Egypt will observe DST from April's last Friday

through October's last Thursday. (Thanks to Ahmad ElDardiry.)

Assume the transition times are 00:00 and 24:00, respectively.

In 2023 Morocco's spring-forward transition after Ramadan

will occur April 23, not April 30. (Thanks to Milamber.)

Adjust predictions for future years accordingly. This affects

predictions for 2023, 2031, 2038, and later years.

This year Palestine will delay its spring forward from

March 25 to April 29 due to Ramadan. (Thanks to Heba Hamad.)

Make guesses for future Ramadans too.

Much of Greenland, represented by America/Nuuk, will continue to

observe DST using European Union rules. When combined with

Greenland's decision not to change the clocks in fall 2023,

America/Nuuk therefore changes from -03/-02 to -02/-01 effective

2023-10-29 at 01:00 UTC. (Thanks to Thomas M. Steenholdt.)

This change from 2022g doesn't affect timestamps until 2024-03-30,

and doesn't affect tm_isdst until 2023-03-25.

Changes to past timestamps

America/Yellowknife has changed from a Zone to a backward

compatibility Link, as it no longer differs from America/Edmonton

since 1970. (Thanks to Almaz Mingaleev.) This affects some

pre-1948 timestamps. The old data are now in 'backzone'.

Changes to past time zone abbreviations

When observing Moscow time, Europe/Kirov and Europe/Volgograd now

use the abbreviations MSK/MSD instead of numeric abbreviations,

for consistency with other timezones observing Moscow time.

Changes to code

You can now tell tzselect local time, to simplify later choices.

Select the 'time' option in its first prompt.

You can now compile with -DTZNAME_MAXIMUM=N to limit time zone

abbreviations to N bytes (default 255). The reference runtime

library now rejects POSIX-style TZ strings that contain longer

abbreviations, treating them as UTC. Previously the limit was

platform dependent and abbreviations were silently truncated to

16 bytes even when the limit was greater than 16.

The code by default is now designed for C99 or later. To build on

a mostly-C89 platform, compile with -DPORT_TO_C89; this should

work on C89 platforms that also support C99 'long long' and

perhaps a few other extensions to C89. To support C89 callers of

tzcode's library, compile with -DSUPPORT_C89; however, this could

trigger latent bugs in C99-or-later callers. The two new macros

are transitional aids planned to be removed in a future version

(say, in 2029), when C99 or later will be required.

The code now builds again on pre-C99 platforms, if you compile

with -DPORT_TO_C89. This fixes a bug introduced in 2022f.

On C23-compatible platforms tzcode no longer uses syntax like

'static [[noreturn]] void usage(void);'. Instead, it uses

'[[noreturn]] static void usage(void);' as strict C23 requires.

(Problem reported by Houge Langley.)

The code's functions now constrain their arguments with the C

'restrict' keyword consistently with their documentation.

This may allow future optimizations.

zdump again builds standalone with ckdadd and without setenv,

fixing a bug introduced in 2022g. (Problem reported by panic.)

leapseconds.awk can now process a leap seconds file that never

expires; this might be useful if leap seconds are discontinued.

Changes to commentary

tz-link.html has a new section "Coordinating with governments and

distributors". (Thanks to Neil Fuller for some of the text.)

To improve tzselect diagnostics, zone1970.tab's comments column is

now limited to countries that have multiple timezones.

Note that there are plans to discontinue leap seconds by 2035.

Release 2022g - 2022-11-29 08:58:31 -0800

Briefly:

The northern edge of Chihuahua changes to US timekeeping.

Much of Greenland stops changing clocks after March 2023.

Fix some pre-1996 timestamps in northern Canada.

C89 is now deprecated; please use C99 or later.

Portability fixes for AIX, libintl, MS-Windows, musl, z/OS

In C code, use more C23 features if available.

C23 timegm now supported by default

Fixes for unlikely integer overflows

Changes to future timestamps

In the Mexican state of Chihuahua, the border strip near the US

will change to agree with nearby US locations on 2022-11-30.

The strip's western part, represented by Ciudad Juárez, switches

from -06 all year to -07/-06 with US DST rules, like El Paso, TX.

The eastern part, represented by Ojinaga, will observe US DST next

year, like Presidio, TX. (Thanks to Heitor David Pinto.)

A new Zone America/Ciudad_Juarez splits from America/Ojinaga.

Much of Greenland, represented by America/Nuuk, stops observing

winter time after March 2023, so its daylight saving time becomes

standard time. (Thanks to Jonas Nyrup and Jürgen Appel.)

Changes to past timestamps

Changes for pre-1996 northern Canada (thanks to Chris Walton):

Merge America/Iqaluit and America/Pangnirtung into the former,

with a backward compatibility link for the latter name.

There is no good evidence the two locations differ since 1970.

This change affects pre-1996 America/Pangnirtung timestamps.

Cambridge Bay, Inuvik, Iqaluit, Rankin Inlet, Resolute and

Yellowknife did not observe DST in 1965, and did observe DST

from 1972 through 1979.

Whitehorse moved from -09 to -08 on 1966-02-27, not 1967-05-28.

Colombia's 1993 fallback was 02-06 24:00, not 04-04 00:00.

(Thanks to Alois Treindl.)

Singapore's 1981-12-31 change was at 16:00 UTC (23:30 local time),

not 24:00 local time. (Thanks to Geoff Clare via Robert Elz.)

Changes to code

Although tzcode still works with C89, bugs found in recent routine

maintenance indicate that bitrot has set in and that in practice

C89 is no longer used to build tzcode. As it is a maintenance

burden, support for C89 is planned to be removed soon. Instead,

please use compilers compatible with C99, C11, C17, or C23.

timegm, which tzcode implemented in 1989, will finally be

standardized 34 years later as part of C23, so timegm is now

supported even if STD_INSPIRED is not defined.

Fix bug in zdump's tzalloc emulation on hosts that lack tm_zone.

(Problem reported by Đoàn Trần Công Danh.)

Fix bug in zic on hosts where malloc(0) yields NULL on success.

(Problem reported by Tim McBrayer for AIX 6.1.)

Fix zic configuration to avoid linkage failures on some platforms.

(Problems reported by Gilmore Davidson and Igor Ivanov.)

Work around MS-Windows nmake incompatibility with POSIX.

(Problem reported by Manuela Friedrich.)

Port mktime and strftime to debugging platforms where accessing

uninitialized data has undefined behavior (strftime problem

reported by Robert Elz).

Check more carefully for unlikely integer overflows, preferring

C23 <stdckdint.h> to overflow checking by hand, as the latter has

had obscure bugs.

Changes to build procedure

New Makefile rule check_mild that skips checking whether Link

lines are in the file 'backward'. (Inspired by a suggestion from

Stephen Colebourne.)

Release 2022f - 2022-10-28 18:04:57 -0700

Briefly:

Mexico will no longer observe DST except near the US border.

Chihuahua moves to year-round -06 on 2022-10-30.

Fiji no longer observes DST.

Move links to 'backward'.

In vanguard form, GMT is now a Zone and Etc/GMT a link.

zic now supports links to links, and vanguard form uses this.

Simplify four Ontario zones.

Fix a Y2438 bug when reading TZif data.

Enable 64-bit time_t on 32-bit glibc platforms.

Omit large-file support when no longer needed.

In C code, use some C23 features if available.

Remove no-longer-needed workaround for Qt bug 53071.

Changes to future timestamps

Mexico will no longer observe DST after 2022, except for areas

near the US border that continue to observe US DST rules.

On 2022-10-30 at 02:00 the Mexican state of Chihuahua moves

from -07 (-06 with DST) to year-round -06, thus not changing

its clocks that day. The new law states that Chihuahua

near the US border no longer observes US DST.

(Thanks to gera for the heads-up about Chihuahua.)

Fiji will not observe DST in 2022/3. (Thanks to Shalvin Narayan.)

For now, assume DST is suspended indefinitely.

Changes to data

Move links to 'backward' to ease and simplify link maintenance.

This affects generated data only if you use 'make BACKWARD='.

GMT is now a Zone and Etc/GMT a link instead of vice versa,

as GMT is needed for leap second support whereas Etc/GMT is not.

However, this change exposes a bug in TZUpdater 2.3.2 so it is

present only in vanguard form for now.

Vanguard form now uses links to links, as zic now supports this.

Changes to past timestamps

Simplify four Ontario zones, as most of the post-1970 differences

seem to have been imaginary. (Problem reported by Chris Walton.)

Move America/Nipigon, America/Rainy_River, and America/Thunder_Bay

to 'backzone'; backward-compatibility links still work, albeit

with some different timestamps before November 2005.

Changes to code

zic now supports links to links regardless of input line order.

For example, if Australia/Sydney is a Zone, the lines

Link Australia/Canberra Australia/ACT

Link Australia/Sydney Australia/Canberra

now work correctly, even though the shell commands

ln Australia/Canberra Australia/ACT

ln Australia/Sydney Australia/Canberra

would fail because the first command attempts to use a link

Australia/Canberra that does not exist until after the second

command is executed. Previously, zic had unspecified behavior if

a Link line's target was another link, and zic often misbehaved if

a Link line's target was a later Link line.

Fix line number in zic's diagnostic for a link to a link.

Fix a bug that caused localtime to mishandle timestamps starting

in the year 2438 when reading data generated by 'zic -b fat' when

distant-future DST transitions occur at times given in standard

time or in UT, not the usual case of local time. This occurs when

the corresponding .zi Rule lines specify DST transitions with TO

columns of 'max' and AT columns that end in 's' or 'u'. The

number 2438 comes from the 32-bit limit in the year 2038, plus the

400-year Gregorian cycle. (Problem reported by Bradley White.)

On glibc 2.34 and later, which optionally supports 64-bit time_t

on platforms like x86 where time_t was traditionally 32 bits,

default time_t to 64 instead of 32 bits. This lets functions like

localtime support timestamps after the year 2038, and fixes

year-2038 problems in zic when accessing files dated after 2038.

To continue to limit time_t to 32 bits on these platforms, use

"make CFLAGS='-D_TIME_BITS=32'".

In C code, do not enable large-file support on platforms like AIX

and macOS that no longer need it now that tzcode does not use

off_t or related functions like 'stat'. Large-file support is

still enabled by default on GNU/Linux, as it is needed for 64-bit

time_t support.

In C code, prefer C23 keywords to pre-C23 macros for alignof,

bool, false, and true. Also, use the following C23 features if

available: __has_include, unreachable.

zic no longer works around Qt bug 53071, as the relevant Qt

releases have been out of support since 2019. This change affects

only fat TZif files, as thin files never had the workaround.

zdump no longer modifies the environ vector when compiled on

platforms lacking tm_zone or when compiled with -DUSE_LTZ=0.

This avoid undefined behavior on POSIX platforms.

Release 2022e - 2022-10-11 11:13:02 -0700

Briefly:

Jordan and Syria switch from +02/+03 with DST to year-round +03.

Changes to future timestamps

Jordan and Syria are abandoning the DST regime and are changing to

permanent +03, so they will not fall back from +03 to +02 on

2022-10-28. (Thanks to Steffen Thorsen and Issam Al-Zuwairi.)

Changes to past timestamps

On 1922-01-01 Tijuana adopted standard time at 00:00, not 01:00.

Changes to past time zone abbreviations and DST flags

The temporary advancement of clocks in central Mexico in summer

1931 is now treated as daylight saving time, instead of as two

changes to standard time.

Release 2022d - 2022-09-23 12:02:57 -0700

Briefly:

Palestine transitions are now Saturdays at 02:00.

Simplify three Ukraine zones into one.

Changes to future timestamps

Palestine now springs forward and falls back at 02:00 on the

first Saturday on or after March 24 and October 24, respectively.

This means 2022 falls back 10-29 at 02:00, not 10-28 at 01:00.

(Thanks to Heba Hamad.)

Changes to past timestamps

Simplify three Ukraine zones to one, since the post-1970

differences seem to have been imaginary. Move Europe/Uzhgorod and

Europe/Zaporozhye to 'backzone'; backward-compatibility links

still work, albeit with different timestamps before October 1991.

Release 2022c - 2022-08-15 17:47:18 -0700

Briefly:

Work around awk bug in FreeBSD, macOS, etc.

Improve tzselect on intercontinental Zones.

Changes to code

Work around a bug in onetrueawk that broke commands like

'make traditional_tarballs' on FreeBSD, macOS, etc.

(Problem reported by Deborah Goldsmith.)

Add code to tzselect that uses experimental structured comments in

zone1970.tab to clarify whether Zones like Africa/Abidjan and

Europe/Istanbul cross continent or ocean boundaries.

(Inspired by a problem reported by Peter Krefting.)

Fix bug with 'zic -d /a/b/c' when /a is unwritable but the

directory /a/b already exists.

Remove zoneinfo2tdf.pl, as it was unused and triggered false

malware alarms on some email servers.

Release 2022b - 2022-08-10 15:38:32 -0700

Briefly:

Chile's DST is delayed by a week in September 2022.

Iran no longer observes DST after 2022.

Rename Europe/Kiev to Europe/Kyiv.

New zic -R option

Vanguard form now uses %z.

Finish moving duplicate-since-1970 zones to 'backzone'.

New build option PACKRATLIST

New tailored_tarballs target, replacing rearguard_tarballs

Changes to future timestamps

Chile's 2022 DST start is delayed from September 4 to September 11.

(Thanks to Juan Correa.)

Iran plans to stop observing DST permanently, after it falls back

on 2022-09-21. (Thanks to Ali Mirjamali.)

Changes to past timestamps

Finish moving to 'backzone' the location-based zones whose

timestamps since 1970 are duplicates; adjust links accordingly.

This change ordinarily affects only pre-1970 timestamps, and with

the new PACKRATLIST option it does not affect any timestamps.

In this round the affected zones are Antarctica/Vostok,

Asia/Brunei, Asia/Kuala_Lumpur, Atlantic/Reykjavik,

Europe/Amsterdam, Europe/Copenhagen, Europe/Luxembourg,

Europe/Monaco, Europe/Oslo, Europe/Stockholm, Indian/Christmas,

Indian/Cocos, Indian/Kerguelen, Indian/Mahe, Indian/Reunion,

Pacific/Chuuk, Pacific/Funafuti, Pacific/Majuro, Pacific/Pohnpei,

Pacific/Wake and Pacific/Wallis, and the affected links are

Arctic/Longyearbyen, Atlantic/Jan_Mayen, Iceland, Pacific/Ponape,

Pacific/Truk, and Pacific/Yap.

From fall 1994 through fall 1995, Shanks wrote that Crimea's

DST transitions were at 02:00 standard time, not at 00:00.

(Thanks to Michael Deckers.)

Iran adopted standard time in 1935, not 1946. In 1977 it observed

DST from 03-21 23:00 to 10-20 24:00; its 1978 transitions were on

03-24 and 08-05, not 03-20 and 10-20; and its spring 1979

transition was on 05-27, not 03-21.

(Thanks to Roozbeh Pournader and Francis Santoni.)

Chile's observance of -04 from 1946-08-29 through 1947-03-31 was

considered DST, not standard time. Santiago and environs had moved

their clocks back to rejoin the rest of mainland Chile; put this

change at the end of 1946-08-28. (Thanks to Michael Deckers.)

Some old, small clock transitions have been removed, as people at

the time did not change their clocks. This affects Asia/Hong_Kong

in 1904, Asia/Ho_Chi_Minh in 1906, and Europe/Dublin in 1880.

Changes to zone name

Rename Europe/Kiev to Europe/Kyiv, as "Kyiv" is more common in

English now. Spelling of other names in Ukraine has not yet

demonstrably changed in common English practice so for now these

names retain old spellings, as in other countries (e.g.,

Europe/Prague not "Praha", and Europe/Sofia not "Sofiya").

Changes to code

zic has a new option '-R @N' to output explicit transitions < N.

(Need suggested by Almaz Mingaleev.)

'zic -r @N' no longer outputs bad data when N < first transition.

(Problem introduced in 2021d and reported by Peter Krefting.)

zic now checks its input for NUL bytes and unterminated lines, and

now supports input line lengths up to 2048 (not 512) bytes.

gmtime and related code now use the abbreviation "UTC" not "GMT".

POSIX is being revised to require this.

When tzset and related functions set vestigial static variables

like tzname, they now prefer specified timestamps to unspecified ones.

(Problem reported by Almaz Mingaleev.)

zic no longer complains "can't determine time zone abbreviation to

use just after until time" when a transition to a new standard

time occurs simultaneously with the first DST fallback transition.

Changes to build procedure

Source data in vanguard form now uses the %z notation, introduced

in release 2015f. For example, for America/Sao_Paulo vanguard

form contains the zone continuation line "-3:00 Brazil %z", which

is simpler and more reliable than the line "-3:00 Brazil -03/-02"

used in main and rearguard forms. The plan is for the main form

to use %z eventually; in the meantime maintainers of zi parsers

are encouraged to test the parsers on vanguard.zi.

The Makefile has a new PACKRATLIST option to select a subset of

'backzone'. For example, 'make PACKRATDATA=backzone

PACKRATLIST=zone.tab' now generates TZif files identical to those

of the global-tz project.

The Makefile has a new tailored_tarballs target for generating

special-purpose tarballs. It generalizes and replaces the

rearguard_tarballs target and related targets and macros, which

are now obsolescent.

'make install' now defaults LOCALTIME to Factory not GMT,

which means the default abbreviation is now "-00" not "GMT".

Remove the posix_packrat target, marked obsolescent in 2016a.

Release 2022a - 2022-03-15 23:02:01 -0700

Briefly:

Palestine will spring forward on 2022-03-27, not -03-26.

zdump -v now outputs better failure indications.

Bug fixes for code that reads corrupted TZif data.

Changes to future timestamps

Palestine will spring forward on 2022-03-27, not 2022-03-26.

(Thanks to Heba Hamad.) Predict future transitions for first

Sunday >= March 25. Additionally, predict fallbacks to be the first

Friday on or after October 23, not October's last Friday, to be more

consistent with recent practice. The first differing fallback

prediction is on 2025-10-24, not 2025-10-31.

Changes to past timestamps

From 1992 through spring 1996, Ukraine's DST transitions were at

02:00 standard time, not at 01:00 UTC. (Thanks to Alois Treindl.)

Chile's Santiago Mean Time and its LMT precursor have been adjusted

eastward by 1 second to align with past and present law.

Changes to commentary

Add several references for Chile's 1946/1947 transitions, some of

which only affected portions of the country.

Changes to code

Fix bug when mktime gets confused by truncated TZif files with

unspecified local time. (Problem reported by Almaz Mingaleev.)

Fix bug when 32-bit time_t code reads malformed 64-bit TZif data.

(Problem reported by Christos Zoulas.)

When reading a version 2 or later TZif file, the TZif reader now

validates the version 1 header and data block only enough to skip

over them, as recommended by RFC 8536 section 4. Also, the TZif

reader no longer mistakenly attempts to parse a version 1 TZIf

file header as a TZ string.

zdump -v now outputs "(localtime failed)" and "(gmtime failed)"

when local time and UT cannot be determined for a timestamp.

Changes to build procedure

Distribution tarballs now use standard POSIX.1-1988 ustar format

instead of GNU format. Although the formats are almost identical

for these tarballs, ustar headers' magic fields contain "ustar"

instead of "ustar ", and their version fields contain "00" instead

of " ". The two formats are planned to diverge more significantly

for tzdb releases after 2242-03-16 12:56:31 UTC, when the ustar

format becomes obsolete and the tarballs switch to pax format, an

extension of ustar. For details about these formats, please see

"pax - portable archive interchange", IEEE Std 1003.1-2017,

<https://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92_13>.

Release 2021e - 2021-10-21 18:41:00 -0700

Changes to future timestamps

Palestine will fall back 10-29 (not 10-30) at 01:00.

(Thanks to P Chan and Heba Hemad.)

Release 2021d - 2021-10-15 13:48:18 -0700

Briefly:

Fiji suspends DST for the 2021/2022 season.

'zic -r' marks unspecified timestamps with "-00".

Changes to future timestamps

Fiji will suspend observance of DST for the 2021/2022 season.

Assume for now that it will return next year. (Thanks to Jashneel

Kumar and P Chan.)

Changes to code

'zic -r' now uses "-00" time zone abbreviations for intervals

with UT offsets that are unspecified due to -r truncation.

This implements a change in draft Internet RFC 8536bis.

Release 2021c - 2021-10-01 14:21:49 -0700

Briefly:

Revert most 2021b changes to 'backward'.

Fix 'zic -b fat' bug in pre-1970 32-bit data.

Fix two Link line typos.

Distribute SECURITY file.

This release is intended as a bugfix release, to fix compatibility

problems and typos reported since 2021b was released.

Changes to Link directives

Revert almost all of 2021b's changes to the 'backward' file,

by moving Link directives back to where they were in 2021a.

Although 'zic' doesn't care which source file contains a Link

directive, some downstream uses ran into trouble with the move.

(Problem reported by Stephen Colebourne for Joda-Time.)

Fix typo that linked Atlantic/Jan_Mayen to the wrong location

(problem reported by Chris Walton).

Fix 'backzone' typo that linked America/Virgin to the wrong

location (problem reported by Michael Deckers).

Changes to code

Fix a bug in 'zic -b fat' that caused old timestamps to be

mishandled in 32-bit-only readers (problem reported by Daniel

Fischer).

Changes to documentation

Distribute the SECURITY file (problem reported by Andreas Radke).

Release 2021b - 2021-09-24 16:23:00 -0700

Briefly:

Jordan now starts DST on February's last Thursday.

Samoa no longer observes DST.

Merge more location-based Zones whose timestamps agree since 1970.

Move some backward-compatibility links to 'backward'.

Rename Pacific/Enderbury to Pacific/Kanton.

Correct many pre-1993 transitions in Malawi, Portugal, etc.

zic now creates each output file or link atomically.

zic -L no longer omits the POSIX TZ string in its output.

zic fixes for truncation and leap second table expiration.

zic now follows POSIX for TZ strings using all-year DST.

Fix some localtime crashes and bugs in obscure cases.

zdump -v now outputs more-useful boundary cases.

tzfile.5 better matches a draft successor to RFC 8536.

A new file SECURITY.

This release is prompted by recent announcements by Jordan and Samoa.

It incorporates many other changes that had accumulated since 2021a.

However, it omits most proposed changes that merged all Zones

agreeing since 1970, as concerns were raised about doing too many of

these changes at once. It does keeps some of these changes in the

interest of making tzdb more equitable one step at a time; see

"Merge more location-based Zones" below.

Changes to future timestamps

Jordan now starts DST on February's last Thursday.

(Thanks to Steffen Thorsen.)

Samoa no longer observes DST. (Thanks to Geoffrey D. Bennett.)

Changes to zone name

Rename Pacific/Enderbury to Pacific/Kanton. When we added

Enderbury in 1993, we did not know that it is uninhabited and that

Kanton (population two dozen) is the only inhabited location in

that timezone. The old name is now a backward-compatibility link.

Changes to past timestamps

Correct many pre-1993 transitions, fixing entries originally

derived from Shanks, Whitman, and Mundell. The fixes include:

- Barbados: standard time was introduced in 1911, not 1932; and

DST was observed in 1942-1944

- Cook Islands: In 1899 they switched from east to west of GMT,

celebrating Christmas for two days. They (and Niue) switched

to standard time in 1952, not 1901.

- Guyana: corrected LMT for Georgetown; the introduction of

standard time in 1911, not 1915; and corrections to 1975 and

1992 transitions

- Kanton: uninhabited before 1937-08-31

- Niue: only observed -11:20 from 1952 through 1964, then went to

-11 instead of -11:30

- Portugal: DST was observed in 1950

- Tonga: corrected LMT; the introduction of standard time in 1945,

not 1901; and corrections to the transition from +12:20 to +13

in 1961, not 1941

Additional fixes to entries in the 'backzone' file include:

- Enderbury: inhabited only 1860/1885 and 1938-03-06/1942-02-09

- The Gambia: 1933 and 1942 transitions

- Malawi: several 1911 through 1925 transitions

- Sierra Leone: several 1913 through 1941 transitions, and DST

was NOT observed in 1957 through 1962

(Thanks to P Chan, Michael Deckers, Alexander Krivenyshev and

Alois Treindl.)

Merge more location-based Zones whose timestamps agree since 1970,

as pre-1970 timestamps are out of scope. This is part of a

process that has been ongoing since 2013. This does not affect

post-1970 timestamps, and timezone historians who build with 'make

PACKRATDATA=backzone' should see no changes to pre-1970 timestamps.

When merging, keep the most-populous location's data, and move

data for other locations to 'backzone' with a backward

link in 'backward'. For example, move America/Creston data to

'backzone' with a link in 'backward' from America/Phoenix because

the two timezones' timestamps agree since 1970; this change

affects some pre-1968 timestamps in America/Creston because

Creston and Phoenix disagreed before 1968. The affected Zones

are Africa/Accra, America/Atikokan, America/Blanc-Sablon,

America/Creston, America/Curacao, America/Nassau,

America/Port_of_Spain, Antarctica/DumontDUrville, and

Antarctica/Syowa.

Changes to maintenance procedure

The new file SECURITY covers how to report security-related bugs.

Several backward-compatibility links have been moved to the

'backward' file. These links, which range from Africa/Addis_Ababa

to Pacific/Saipan, are only for compatibility with now-obsolete

guidelines suggesting an entry for every ISO 3166 code.

The intercontinental convenience links Asia/Istanbul and

Europe/Nicosia have also been moved to 'backward'.

Changes to code

zic now creates each output file or link atomically,

possibly by creating a temporary file and then renaming it.

This avoids races where a TZ setting would temporarily stop

working while zic was installing a replacement file or link.

zic -L no longer omits the POSIX TZ string in its output.

Starting with 2020a, zic -L truncated its output according to the

"Expires" directive or "#expires" comment in the leapseconds file.

The resulting TZif files omitted daylight saving transitions after

the leap second table expired, which led to far less accurate

predictions of times after the expiry. Although future timestamps

cannot be converted accurately in the presence of leap seconds, it

is more accurate to convert near-future timestamps with a few

seconds error than with an hour error, so zic -L no longer