Time Zone Database

https://www.iana.org/time-zones
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The Time Zone Database contains code and data representing the history of local time worldwide,...
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### Configure Build and Installation Options

Source: https://www.iana.org/time-zones/releases/2017c

Commands for customizing the installation of time zone data files and build behavior.

```bash
make TZDATA_TEXT=
```

```bash
make TZDATA_TEXT=tzdata.zi
```

```bash
make BACKWARD=
```

```bash
make check
```

--------------------------------

### Zone record with specific daylight saving time amount

Source: https://www.iana.org/time-zones/tz-how-to

Example showing the use of a specific time amount (1:00) in the RULES column to indicate daylight saving time.

```text
#Zone NAME            STDOFF RULES FORMAT [UNTIL]
Zone Pacific/Honolulu ...                 1933 Apr 30  2:00
                      -10:30 1:00  HDT    1933 May 21 12:00
                      ...
```

--------------------------------

### US Rule Definitions in tz Database

Source: https://www.iana.org/time-zones/tz-how-to

Example of Rule entries defining daylight saving time transitions for the US.

```text
#Rule NAME FROM TO    -   IN  ON        AT   SAVE LETTER/S
Rule  US   1918 1919  -   Mar lastSun  2:00  1:00 D
Rule  US   1918 1919  -   Oct lastSun  2:00  0    S
Rule  US   1942 only  -   Feb 9        2:00  1:00 W # War
Rule  US   1945 only  -   Aug 14      23:00u 1:00 P # Peace
Rule  US   1945 only  -   Sep 30       2:00  0    S
Rule  US   1967 2006  -   Oct lastSun  2:00  0    S
Rule  US   1967 1973  -   Apr lastSun  2:00  1:00 D
Rule  US   1974 only  -   Jan 6        2:00  1:00 D
Rule  US   1975 only  -   Feb 23       2:00  1:00 D
Rule  US   1976 1986  -   Apr lastSun  2:00  1:00 D
Rule  US   1987 2006  -   Apr Sun>=1   2:00  1:00 D
Rule  US   2007 max   -   Mar Sun>=8   2:00  1:00 D
Rule  US   2007 max   -   Nov Sun>=1   2:00  0    S
```

--------------------------------

### Build and Compile Options

Source: https://www.iana.org/time-zones/releases/2026a

Configuration commands for building the database and compiler flags for runtime behavior.

```bash
make REDO=posix_right
```

```bash
make REDO=right_only
```

```bash
-DTZ_RUNTIME_LEAPS=0
```

```bash
zic -v
```

```bash
zic -L
```

```bash
zic -p
```

```bash
-DSTD_INSPIRED
```

--------------------------------

### Release Notes for 2012i

Source: https://www.iana.org/time-zones/releases/2012i

Summary of changes including configuration updates for Cuba, build system enhancements, and new Makefile targets.

```text
  Cuba switches from DST tomorrow at 01:00.  (Thanks to Steffen Thorsen.)

  Linker flags can now be specified via LDFLAGS.
  AWK now defaults to 'awk', not 'nawk'.
  The shell in tzselect now defaults to /bin/bash, but this can
  be overridden by specifying KSHELL.
  The main web page now mentions the unofficial GitHub repository.
  (Thanks to Mike Frysinger.)

  Tarball signatures can now be built by running 'make signatures'.
  There are also new makefile rules 'tarballs', 'check_public', and
  separate makefile rules for each tarball and signature file.
  A few makefile rules are now more portable to strict POSIX.

  The main web page now lists the canonical IANA URL.
```

--------------------------------

### Complete Hawaii Time Zone History Record

Source: https://www.iana.org/time-zones/tz-how-to

A comprehensive example showing Rule definitions and the corresponding Zone record for Pacific/Honolulu.

```text
# Relevant Excerpts from the US Rules
#Rule NAME FROM TO   -    IN  ON      AT     SAVE LETTER/S
Rule  US   1918 1919 -    Oct lastSun  2:00  0    S
Rule  US   1942 only -    Feb  9       2:00  1:00 W # War
Rule  US   1945 only -    Aug 14      23:00u 1:00 P # Peace
Rule  US   1945 only -    Sep lastSun  2:00  0    S

# The Zone Record
#Zone NAME            STDOFF    RULES FORMAT [UNTIL]
Zone Pacific/Honolulu -10:31:26 -     LMT    1896 Jan 13 12:00
                      -10:30    -     HST    1933 Apr 30  2:00
                      -10:30    1:00  HDT    1933 May 21  2:00
                      -10:30    US    H%sT   1947 Jun  8  2:00
                      -10:00    -     HST
```

--------------------------------

### Configure zdump with system library

Source: https://www.iana.org/time-zones/releases/2014g

Use this make command to build zdump using the system library instead of the tz library.

```bash
make CFLAGS=-DUSE_LTZ=0 TZDOBJS=zdump.o CHECK_TIME_T_ALTERNATIVES=
```

--------------------------------

### zic compiler command usage

Source: https://www.iana.org/time-zones/releases/2025b

Example of a zic command that previously caused incorrect symlink creation and read buffer underflow.

```bash
zic -l TIMEZONE -d . -l /some/other/file/system
```

--------------------------------

### Represent far-future timestamps with POSIX-like TZ strings

Source: https://www.iana.org/time-zones/releases/2013e

Example of a TZ string using an extended hour range for far-future timestamps in Fiji.

```text
TZ='FJT-12FJST,M10.3.1/146,M1.3.4/75'
```

--------------------------------

### Release 2010c Change Notes

Source: https://www.iana.org/time-zones/releases/2010c

Technical notes regarding structural changes to initialization logic.

```text
  changes including KRE's suggestion for earlier initialization of
  "goahead" and "goback" structure elements
```

--------------------------------

### Release Notes Summary

Source: https://www.iana.org/time-zones/releases/2010m

Summary of changes included in the 2010m release.

```text
  Hong Kong, Vostok, and zic.c changes
```

--------------------------------

### Define a Zone Record with Slash-Separated Abbreviations

Source: https://www.iana.org/time-zones/tz-how-to

Example of using a slash in the FORMAT column to specify standard and daylight saving time abbreviations.

```text
#Zone NAME          STDOFF RULES FORMAT  [UNTIL]
Zone  Europe/London ...                  1996
                    0:00   EU    GMT/BST
```

--------------------------------

### Release Notes Content

Source: https://www.iana.org/time-zones/releases/96k

Contains the summary of changes for the 96k release.

```text
  the latest round of changes from Paul Eggert

  the recent Year 2000 material
```

--------------------------------

### Zone record structure for America/Chicago

Source: https://www.iana.org/time-zones/tz-how-to

Example of a Zone record showing multiple continuation lines defining time offsets and rules over time.

```text
#Zone       NAME      STDOFF   RULES FORMAT [UNTIL]
Zone  America/Chicago -5:50:36 -       LMT  1883 Nov 18 12:09:24
                      -6:00    US      C%sT 1920
                      -6:00    Chicago C%sT 1936 Mar  1  2:00
                      -5:00    -       EST  1936 Nov 15  2:00
                      -6:00    Chicago C%sT 1942
                      -6:00    US      C%sT 1946
                      -6:00    Chicago C%sT 1967
                      -6:00    US      C%sT
```

--------------------------------

### Makefile and TZif format updates

Source: https://www.iana.org/time-zones/releases/code1997h-data1997j

Contains release notes regarding TZif file headers and the addition of a zones target to the Makefile.

```text
  minor changes to put "TZif" at the start of each timezone information file

  a rule has also been added to the Makefile so you can
	make zones
  to just recompile the zone information files (rather than doing a
  full "make install" with its other effects).
```

--------------------------------

### Define a Geographical TZ String

Source: https://www.iana.org/time-zones/theory

Example of using a geographical identifier for time zone configuration, which is more accurate and easier to manage than proleptic strings.

```text
TZ='Pacific/Auckland'
```

--------------------------------

### Run time_t alternative tests

Source: https://www.iana.org/time-zones/releases/2013d

Execute the make command to test time_t types other than the system default.

```bash
make check_time_t_alternatives
```

--------------------------------

### Configure DATAFORM in Makefile

Source: https://www.iana.org/time-zones/releases/2018d

The DATAFORM macro allows installers to choose between vanguard, main, and rearguard source data formats to manage downstream compatibility.

```makefile
DATAFORM=vanguard
DATAFORM=main
DATAFORM=rearguard
```

--------------------------------

### Define Chicago Daylight Saving Time Rules

Source: https://www.iana.org/time-zones/tz-how-to

Example of Rule lines from the northamerica data file defining daylight saving time transitions for Chicago.

```text
#Rule NAME    FROM TO    -   IN  ON      AT   SAVE LETTER
Rule  Chicago 1920 only  -   Jun 13      2:00 1:00 D
Rule  Chicago 1920 1921  -   Oct lastSun 2:00 0    S
Rule  Chicago 1921 only  -   Mar lastSun 2:00 1:00 D
Rule  Chicago 1922 1966  -   Apr lastSun 2:00 1:00 D
Rule  Chicago 1922 1954  -   Sep lastSun 2:00 0    S
Rule  Chicago 1955 1966  -   Oct lastSun 2:00 0    S
```

--------------------------------

### Build command for leap seconds and backzone

Source: https://www.iana.org/time-zones/releases/2016a

Use this command to combine leap seconds with the backzone file during the build process.

```bash
make PACKRATDATA=backzone REDO=posix_right zones
```

--------------------------------

### Represent all-year daylight saving time with POSIX-like TZ strings

Source: https://www.iana.org/time-zones/releases/2013e

Example of a TZ string configured for Western Argentina Summer Time to remain in effect all year.

```text
TZ='WART4WARST,J1/0,J365/25'
```

--------------------------------

### Define a Proleptic TZ String for New Zealand

Source: https://www.iana.org/time-zones/theory

Example of a complex proleptic TZ string specifying standard time and daylight saving rules for New Zealand after 2007.

```text
TZ='NZST-12NZDT,M9.5.0,M4.1.0/3'
```

--------------------------------

### Release Notes Configuration Changes

Source: https://www.iana.org/time-zones/releases/2000e

Details regarding data modifications and constant definitions for the 2000e release.

```text
  data changes by Paul Eggert

  a change to the default value of the defined constant HAVE_STRERROR

  the addition of a Dave Barry quote on DST to the tz-arts file
```

--------------------------------

### Release Notes Snippet

Source: https://www.iana.org/time-zones/releases/2005r

Contains release notes regarding Canadian time zone changes and zdump.c logic updates.

```text
  Canadian changes by Paul Eggert

  They also add "<pre>" directives to time zone data files and reflect
  changes to warning message logic in "zdump.c" (but with calls to
  "gettext" kept unbundled at the suggestion of Ken Pizzini).
```

--------------------------------

### Release notes for code96l

Source: https://www.iana.org/time-zones/releases/code96l

Notes indicating that the previous release was missing components.

```text
  tzcode96k was missing a couple of pieces.
```

--------------------------------

### Release Notes Summary

Source: https://www.iana.org/time-zones/releases/2009r

Displays the specific changes included in the 2009r release.

```text
  "antarctica" and "tz-link.htm" changes
```

--------------------------------

### Clone tz database repository

Source: https://www.iana.org/time-zones/tz-link

Retrieves the development repository of code and data from GitHub.

```bash
git clone https://github.com/eggert/tz
```
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