Talk:Unix time

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Please make the shortcomings clearer[edit]

The main article says some words about "not counting" leap seconds, but does not emphasize what inaccuracy and not-well-definedness results from this. From "forgetting" the leap seconds follows that

  • There is no well-defined "epoch". In 1975 the epoch was 1970-01-01 00:00:04 UTC; in 1980 the epoch was 1970-01-01 00:00:09 UTC, and so on. (So the sentence in the article saying "The Unix epoch is the time 00:00:00 UTC on 1 January 1970." is not true.)
  • For the question "what time is now (UTC)" the Unix time is (almost always) correct. But for questions like "what was the time (what year, month, day, hour, minute, second, UTC) 100000000 seconds before now", the Unix time is erronoeus. It incorrectly states that in that time the UTC ...hours and seconds were thisandthat. Similar is true for future dates.

Mhoeygii (talk) 02:18, 12 November 2015 (UTC)

Do you have any reliable sources to back up what you're saying? - Aoidh (talk) 23:17, 13 November 2015 (UTC)

External links modified[edit]

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Cheers.—cyberbot IITalk to my owner:Online 19:53, 28 February 2016 (UTC)

The Wayback Machine link didn't work, but the article is still online, so I updated the link. (It's behind Rupert's paywall - which may account for why the Wayback Machine link didn't work.) Guy Harris (talk) 20:37, 28 February 2016 (UTC)

Does any system really keep a time a a pure linear count of seconds elapsed since 1970-01-01T00:00:00 *TAI*?[edit]

The Olson code (IANA tzdb reference implementation) can, if the leap seconds files are being used, convert a pure linear count of seconds elapsed since 1970-01-01T00:00:00 UTC to a UTC label such as 2015-06-30T23:59:60 UTC. It's not expecting a different-by-23-seconds pure linear count of seconds since 1970-01-01T00:00:00 TAI.

If a system were to keep a pure linear count of seconds since 1970-01-01T00:00:00 TAI, then a gmtime() implementation not taking leap seconds into account (such as the Olson code without the leap seconds files) would convert that to a TAI label. Guy Harris (talk) 19:51, 23 April 2016 (UTC)

Negative values of "seconds since the Epoch"?[edit]

I see nothing in the standard that clearly indicates that negative values of "seconds since the Epoch" are required; time_t is specified in the page on <sys/types.h> only to be "an integer type"; size_t is specified as being "an unsigned integer type" and ssize_t and some other types are specified as being "signed integer types", so this seems to indicate that the current Single UNIX Specification allows time_t to be signed or unsigned. Guy Harris (talk) 18:28, 20 June 2016 (UTC)

What is more, the source cited ("The Open Group Base Specifications Issue 7, section 4.15 Seconds Since the Epoch". The Open Group. Retrieved May 2, 2014. ) says:
"If the year is <1970 or the value is negative, the relationship [between POSIX time and UTC] is undefined."
(The signedness is in this article explained to be for enabling representation of older dates, while the reason I have heard is to make calculating differences in time more straightforward.)
--LPfi (talk) 21:41, 20 June 2016 (UTC)

Bad Terminology: Epoch Time[edit]

I've tried a simple edit in the past, but it was undone. Basically, there are a lot of people using the term "epoch time" on other sites and pointing here as proof that it is valid. The word "epoch" is a simple English noun, and Wikipedia describes it well in Epoch (reference date), which also has a list of other epochs used in computing. By inventing this term "epoch time", we've started a vocabulary of programmers saying things like "I have an epoch of 1499289809..." which is of course erroneous, as the epoch would always be 0 of any form of timestamp, and is explicitly 1970-01-01 00:00:00 UTC for Unix Time.

Can we please remove the "epoch time" terminology and add a paragraph explaining that this usage is erroneous and should be avoided? We can leave the redirect in place so people find it. Thanks.

mj1856 (talk) 21:26, 5 July 2017 (UTC)

I've asked for a citation on UNIX/POSIX time being called "epoch time". Unless somebody can cough up such a citation - a citation not saying "well, Wikipedia links Epoch time to Unix time", as that would be a clear case of citogenesis - that claim should be removed from the article, and the redirect removed. Guy Harris (talk) 21:57, 5 July 2017 (UTC)

"Command line" section too short?[edit]

I feel like a one-sentence section is not really worth it - could that be merged into another section or could the section be expanded? If not, I think the section should be removed entirely. Thoughts?--
└─post by kenny2wiki  Talk  Contribs  04:15, 16 September 2017 (UTC)

This is such a key aspect that it seems worth having a section, so that it is very easy to find. But it seems like it should be fleshed out more, with examples?- (talk) 18:41, 18 November 2017 (UTC)

example good - decoder wanted[edit]

The prominent real-word example of actual CurrentTime near the beginning of the article is a very good feature. But not being able to find a link to a working online decoder is frustrating...- (talk) 18:48, 18 November 2017 (UTC)

Ooops - the current link at the end of the article to * / redirects to


which does work, but is somewhat tricky/frustrating.


does work


also does work.- (talk) 19:05, 18 November 2017 (UTC)

script issues[edit]

As with many videos and etc. that Iv'e seen, i think a section about the flaws should be added. For example, Iphone Ios 7&8 will permanently fail if the date is manually set to January 1, 1970. There are probably other similar issues out there, and i think it would be nice to add a section about them. The garmine (talk) 05:07, 24 April 2018 (UTC)