tz database
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| tz database | |
|---|---|
 | |
| Name | tz database |
| Alternative names | IANA Time Zone Database, zoneinfo |
| Initial release | 1986 |
| Developers | Arthur David Olson, Paul Eggert, IANA |
| Latest release | (see Internet Assigned Numbers Authority) |
| Repository | IANA |
| License | Public domain / permissive |
tz database
The tz database is a collaborative compilation of historical and current civil time zone information for locations worldwide, used by Unix-derived systems, Linux distributions, and many software platforms. It provides zone identifiers, transition rules, and metadata that enable consistent handling of local time across applications such as PostgreSQL, Java (programming language), Python (programming language), and Microsoft Windows-aware services. Widely referenced by operating systems, libraries, and standards bodies, the database underpins time-sensitive infrastructure including IETF protocols, aviation scheduling with International Air Transport Association, and global financial systems like SWIFT.
Overview
The project aggregates records of offset changes, daylight saving time adjustments, and past timekeeping practices for geopolitical entities including United States, United Kingdom, Russia, China, and Australia. Maintained as plain text source files, it outputs binary zoneinfo files compatible with POSIX time functions and runtime libraries such as glibc, musl, and tzdata packages used by Debian and Red Hat Enterprise Linux. The dataset enables conversion between UTC and local times for historical dates relevant to disciplines like astronomy, genealogy, legal history, and transportation.
History and development
Initiated in 1986, the project grew from the needs of Unix system administrators and researchers to represent complex local time histories across jurisdictions. Key contributors include Arthur David Olson and Paul Eggert, who coordinated changes and releases while collaborating with institutions such as IANA and user communities from FreeBSD, NetBSD, OpenBSD, Linux Foundation projects, and commercial vendors. Over successive releases the dataset incorporated legislative changes from national assemblies like the United States Congress, rulings from executive branches in countries like Brazil, and archival material from organizations such as the Royal Observatory Greenwich and national archives.
Structure and file formats
Source files are organized into domain-specific text files (commonly named by region: e.g., Africa, America, Europe) containing Rules, Zone, and Link entries. The files compile into binary zoneinfo using utilities often bundled with tzcode; binaries follow formats consumed by C libraries implementing the ANSI C time APIs and POSIX functions. The database also includes a versioning file and machine-readable metadata used by toolchains in projects such as ICU, Boost (C++) libraries, and Qt (framework). Packaging is provided for distributions like Ubuntu, Fedora, and Arch Linux.
Time zone identifiers and naming conventions
Zone identifiers use the "Area/Location" pattern, naming entries after principal cities or regions such as Europe/London, America/New_York, Asia/Tokyo, and Pacific/Auckland. Names favor stable, well-known locations to minimize churn when political boundaries shift, with convention influenced by toponymy authorities like United Nations Group of Experts on Geographical Names and national naming bodies. Alias entries (Link) provide compatibility with historical or vendor-specific names used by systems from Microsoft and legacy Novell installations. Identifier stability supports interoperability across middleware like NTP daemons, schedulers in Kubernetes, and container runtimes maintained by Docker.
Maintenance and governance
Development and releases are coordinated by maintainers affiliated with communities and organizations such as IANA, volunteer contributors, and maintainers of projects including FreeBSD and glibc. Change adjudication relies on primary sources: national legislation, government gazettes from countries like India and France, and official bulletins from agencies such as U.S. Department of Transportation. Debate and coordination occur on mailing lists, issue trackers hosted by projects like GitHub mirrors, and in discussions involving standards bodies including IETF and regional internet registries.
Usage and implementations
Implementations span operating systems and libraries: glibc on GNU/Linux, musl in lightweight distributions, Bionic (Android) on Android, tzdata packages in BSD ports, and adaptations in Java Virtual Machine runtimes and ICU internationalization libraries. Applications using the dataset include database systems such as PostgreSQL and MySQL, calendaring services like Google Calendar integrations, and programming environments in Ruby, Go (programming language), and Node.js. Third-party services for flight booking, financial settlement engines at institutions such as NASDAQ, and logging infrastructures in cloud platforms by Amazon Web Services and Google Cloud Platform depend on consistent time zone data.
Limitations and controversies
The database faces challenges: geopolitical names and boundaries sometimes conflict with recognition by entities such as United Nations members, causing disputes when toponyms imply sovereignty. Rapid, late legislative changes—seen in cases involving Russia and some South American states—can outpace release cycles, affecting downstream systems like air traffic control scheduling. The choice of representative cities can be contested by national agencies; compatibility with proprietary systems from Microsoft or legacy datasets has required maintaining numerous Link aliases. Licensing and attribution debates arose historically around contributions and reuse by corporations, prompting discussions involving organizations such as Creative Commons-oriented communities and archival institutions.