Editing Time zone (section)

==== Unix ====
{{Main|Unix time}}

[[Unix-like]] systems, including [[Linux]] and [[macOS]], keep system time in [[Unix time]] format, representing the number of seconds that have elapsed since 00:00:00 [[Coordinated Universal Time]] (UTC) on Thursday, January 1, 1970, excluding [[leap second]]s.<ref name="single-unix-spec-4.16">{{cite web|url=http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_16|title=The Open Group Base Specifications Issue 7, section 4.16 Seconds Since the Epoch|publisher=[[The Open Group]]|access-date=January 22, 2017|archive-date=December 22, 2017|archive-url=https://web.archive.org/web/20171222113543/http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_16|url-status=live}}</ref> Unix time is usually converted to local time when displayed to the user, and times specified by the user in local time are converted to Unix time.  The conversion takes into account the time zone and daylight saving time rules; by default the time zone and daylight saving time rules are set up when the system is configured, though individual processes can specify time zones and daylight saving time rules using the ''TZ'' [[environment variable]].<ref name="tzset(3)">{{man|sh|tzset|SUS}}</ref> This allows users in multiple time zones, or in the same time zone but with different daylight saving time rules, to use the same computer, with their respective local times displayed correctly to each user. Information about time zones and daylight saving time rules most commonly comes from the [[IANA time zone database]]. Many systems, including anything using the [[GNU C Library]], a C library based on the [[BSD]] C library, or the [[System V Release 4]] C library, can make use of the IANA time zone database.