The Time Zone Information Format (TZif)
RFC 8536

Document Type RFC - Proposed Standard (February 2019; No errata)
Was draft-murchison-tzdist-tzif (individual in art area)
Last updated 2019-02-12
Stream IETF
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Document shepherd Eliot Lear
Shepherd write-up Show (last changed 2018-08-23)
IESG IESG state RFC 8536 (Proposed Standard)
Consensus Boilerplate Yes
Telechat date
Responsible AD Alexey Melnikov
Send notices to tzdist-bis@ietf.org
IANA IANA review state IANA OK - Actions Needed
IANA action state RFC-Ed-Ack
Internet Engineering Task Force (IETF)                          A. Olson
Request for Comments: 8536
Category: Standards Track                                      P. Eggert
ISSN: 2070-1721                                                     UCLA
                                                            K. Murchison
                                                                FastMail
                                                           February 2019

                The Time Zone Information Format (TZif)

Abstract

   This document specifies the Time Zone Information Format (TZif) for
   representing and exchanging time zone information, independent of any
   particular service or protocol.  Two media types for this format are
   also defined.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8536.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Olson, et al.                Standards Track                    [Page 1]
RFC 8536                          TZif                     February 2019

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  The Time Zone Information Format (TZif) . . . . . . . . . . .   5
     3.1.  TZif Header . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  TZif Data Block . . . . . . . . . . . . . . . . . . . . .   8
     3.3.  TZif Footer . . . . . . . . . . . . . . . . . . . . . . .  12
       3.3.1.  TZ String Extensions  . . . . . . . . . . . . . . . .  13
   4.  Interoperability Considerations . . . . . . . . . . . . . . .  13
   5.  Use with the Time Zone Data Distribution Service  . . . . . .  14
     5.1.  Truncating TZif Files . . . . . . . . . . . . . . . . . .  15
     5.2.  Example TZDIST Request for TZif Data  . . . . . . . . . .  15
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  17
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     8.1.  application/tzif  . . . . . . . . . . . . . . . . . . . .  17
     8.2.  application/tzif-leap . . . . . . . . . . . . . . . . . .  18
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  20
   Appendix A.  Common Interoperability Issues . . . . . . . . . . .  21
   Appendix B.  Example TZif Files . . . . . . . . . . . . . . . . .  23
     B.1.  Version 1 File Representing UTC (with Leap Seconds) . . .  24
     B.2.  Version 2 File Representing Pacific/Honolulu  . . . . . .  28
     B.3.  Truncated Version 3 File Representing Asia/Jerusalem  . .  33
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  34
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  34

Olson, et al.                Standards Track                    [Page 2]
RFC 8536                          TZif                     February 2019

1.  Introduction

   Time zone data typically consists of offsets from universal time
   (UT), daylight saving transition rules, one or more local time
   designations (acronyms or abbreviations), and optional leap-second
   adjustments.  One such format for conveying this information is
   iCalendar [RFC5545].  It is a text-based format used by calendaring
   and scheduling systems.

   This document specifies the widely deployed Time Zone Information
   Format (TZif).  It is a binary format used by most UNIX systems to
   calculate local time.  This format was introduced in the 1980s and
   has evolved since then into multiple upward-compatible versions.
   There is a wide variety of interoperable software capable of
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