time_t - jwz

Dali Clock in the wild

jwz — Sat, 03 Jan 2026 21:35:11 +0000

Our New Years Eve countdown featured Dali Clock, because we use all parts of the buffalo here at org du jwz. And yes, it was NTP synchronized to within 1 frame, thanks for asking.

▶︎

Previously, previously, previously, previously.

Y2232 bug?

jwz — Wed, 07 May 2025 02:17:02 +0000

Debian 12.9:

# date Tue 6 May 19:05:57 PDT 2025 # sudo systemctl stop systemd-timesyncd.service # sudo date -s '2232-04-18 16:47:16' date: cannot set date: Invalid argument Wed 18 Apr 16:47:16 PDT 2232 Exit 1 # date Tue 6 May 19:06:14 PDT 2025 # sudo date -s '2232-04-18 16:47:15' Wed 18 Apr 16:47:15 PDT 2232 # sleep 30 ; date Wed 18 Apr 16:47:45 PDT 2232

The cutoff is 0x1ED5D7403.

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A tale from the time_t mines:

jwz — Sat, 11 Jan 2025 00:04:20 +0000

rachelbythebay:

We ended up with something like 20 hours to smear off a single second.
The end of June approached, and it was time to do a full-scale test. I wanted to be sure that we could survive being a second out of whack without having the confounding factor of the whole rest of the world simultaneously dealing with their own leap second stuff. We needed to know if we'd be okay, and the only way to know was to smear it off, hold a bit to see if anything happened, then smear it back on.

Previously, previously, previously, previously, previously, previously, previously, previously, previously, previously.

Medieval Dick Pics Calendar

jwz — Sat, 14 Dec 2024 22:15:22 +0000

This is a real thing that you can buy. I can't tell who made it, but it is available from your favorite sweatshop retailers.

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Hit a Y2038 bug and it's not even Daylight Savings Day

jwz — Wed, 23 Oct 2024 03:15:55 +0000

 function default_end_date() { - return (date ('Y') + 20) . date ('-m-d 00:00:00');
+ return ('2038-01-18 19:14:07'); // LOL we're all gonna die + // mysqli_sql_exception: Incorrect datetime value: '2044-10-22 00:00:00'
 }

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Contrafactuals

jwz — Fri, 18 Oct 2024 22:56:55 +0000

Making a list of pros and cons of getting in a time machine and going back to 1992 to run a nightclub.

Cons:

Everyone smokes inside, all the time, everywhere. So disgusting.

Pros:

Literally everything about:
- The entertainment industry;
- The music industry;
- The economy;
- The feasibility of running a small business;
- Housing costs;
- Artistic culture.
Live Nation doesn't exist.
AEG doesn't exist.
APE doesn't exist.
TicketMaster is a hardware company.
Frequency of needing to retain a lawyer:
- 90s -- twice a decade.
- Now -- twice a month.
Never need to learn what an Injury and Illness Prevention Program Model Plan is.
Nobody has a mobile phone.
CASH ONLY.

Plus! I'd get to watch the stillbirth of the web!

Without me, Netscape's first release is a year later and Windows only (Mac version coming soon!), but nobody notices because Microsoft already bought Spry as well as Spyglass. "DOC" is a first class file format in their browser. Compuserve and AOL are resurgent as the Linux-level also-rans to Microsoft Chat Rooms. There is no open web. Palm buys Apple then they too get acquired by MS.

And this has a classic Twilight Zone / It's a Wonderful Life ending built right in!

In late November 2000 I look up from reading a newspaper (for newspapers still exist) and realize that Microsoft's censorious dominance over "chat" prevents the Brooks Brothers Riot from happening, we get President Gore, and are on track for 2°C.

But The Past Sucks!

I used to be Team Coupland on this. He noted that every time travel fantasy comes with a list of conditions: "but I have to be gentry", "I have to have my vaccinations and espresso".

"The only sure thing about the past is some ghastly disease, carnage, toil that defies all description, starvation, and boredom of a sort that makes waiting in line at the DMV seem like Disneyland on heroin."

I used to believe that every previous decade was materially worse than the one following, in terms of quality of life, liberty, tolerance, chance of sudden horrific death, creativity, etc.

But now I think that ended around Y2K.

When The Matrix pegged 1999 as the peak of human culture, we laughed. Who's laughing now?

Or as Hunter S. Thompson said, way back in 1971,

"We had all the momentum; we were riding the crest of a high and beautiful wave... So now, less than five years later, you can go up on a steep hill in Las Vegas and look West, and with the right kind of eyes you can almost see the high-water mark -- that place where the wave finally broke and rolled back."

This missive written on my phone, with my thumbs, while leaning against my bar as a truly deplorable band plays.

Enter the shimmering arc.

Previously, previously, previously, previously, previously.

GeoChron

jwz — Thu, 30 May 2024 22:59:45 +0000

The greatest clock (and map) ever made:

▶︎

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BreakTime

jwz — Mon, 06 May 2024 18:46:12 +0000

Decline calendar invites by playing Breakout:

Previously.

Global Warming Is Slowing the Earth's Rotation

jwz — Fri, 29 Mar 2024 02:32:55 +0000

Negative leap second approaching; appalling shitshow to result.

"This is another one of those 'this has never happened before' things that we're seeing from global warming: the idea that this effect is large enough to change the rotation of the entire Earth," says study co-author Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography.
The mass of the miles-thick ice sheets that cover Greenland and Antarctica exerts a strong gravitational pull on the oceans. As the ice sheets melt, all that mass shifts away from the poles and toward the equator, reducing that pull and also causing Earth's rotation to slow down. To understand why this happens, picture a figure skater gracefully spinning on the ice with their arms tucked tightly around their head. As they gradually lower their arms and extend those limbs outward, their spin slows down. [...]
What Agnew found is that the slowdown caused by polar ice melt has been effectively masking a speedup of Earth's rotation caused by changes in the rotation of our liquid outer core. Over the past 50 years, a day has become about 0.0025 second shorter. If global warming never happened, we would likely have needed to subtract a leap second sooner. But with the influence of warming, Agnew estimates, we will need to do so by around 2028 or 2029, although he admits his prediction is uncertain. "There's never been a negative leap second before, and leap seconds themselves have always been a problem for people running computer networks," Agnew says, given that many crucial systems rely on precise timekeeping. "Having to include a negative leap second would be a bigger problem because they've never had to do it."

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time_t is not GMT

jwz — Sun, 10 Mar 2024 23:48:09 +0000

When I hear someone say "a Unix timestamp is in GMT" I die a little inside. It is muddy thinking that leads to many of the problems that plague this modern world.

A time_t does not have a time zone at all. It is a point in time, a scalar value. A 'struct tm' is a point in spacetime, a vector value.

If you are trying to express a point in time to a human, you could do that by saying "1,710,111,386 seconds after the Epoch", but while precise, it's not very readable, so instead you might choose to convert that from a point in time to a point in spacetime instead, and say "2024-03-10 15:56:26 PDT". But those two are not the same thing. You converted a scalar to a vector by picking an arbitrary position in space to attach to it.

The Unix Epoch, the point in time when a time_t is numerically zero, is commonly defined as being at midnight on a particular date in England, but it could just as easily have been defined as having been at 4PM on a particular date in California, or as some number of nanoseconds since the Big Bang. There's nothing "GMT" or "UTC" about it, except that when converted to a human-readable string situated in England, that text has some extra zeroes in it and humans find zeroes comforting.

The number of seconds since that point in time does not change depending on my point in space. (Mostly.)

("GMT" is a time zone and "UTC" is not, but both are points in spacetime where that point happens to be the Royal Observatory. The Platinum-Iridium Reference Zero is of course stored in an evacuated vault in the basement of Pavillon de Breteuil.)

This has been a Public Service Announcement from The Paladin of the Lost Hour.

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List of 2024 Leap Day Bugs

jwz — Sun, 03 Mar 2024 19:09:21 +0000

Code of Matt: (My favorite is this one):

Street lighting in Paris, France was inadvertently turned off at midnight at the start of February 29th, according to reporting by Le Parisien, a French daily newspaper. The operator, Cielis, told the reporter that the problem was linked to a programming fault related to the leap day. It took several hours for lighting to be manually restored.

Previously, previously, previously, previously.

DNA Lounge: Wherein nobody noticed my prank

jwz — Sat, 02 Mar 2024 19:18:20 +0000

April Fools day is for losers, it's worse than Santacon, but Leap Day! Well. Nobody* noticed my hilarious Leap Day prank. For the last two days, March 1st was displayed on our calendar and flyers as Februrary 30th.

I realize this joke is extremely niche, but I expected at least that one of our promoters would be freaking out and my phone would be blowing up. But it didn't happen!

CALENDAR FACT! Did you know that the extra day in February is not the last day of the month? No! The extra day is February 24th, also known as Bissextus, the "Second Sixth". Prior to the 15th century, the last day of February was still the 28th, but the 24th happened twice. And honestly, I think we should still do it that way, just out of pure Chaos Monkey spirit.

Due to various youthful indiscretions, Calendrical Calculations has ended up being one of my Dream Jeopardy Categories. Ask me about Easter.**

Anyway, when I was hacking Ye Olde Webbe Syte to do this thing my first approach was to just wrap localtime and make it lie about mon and dotm but then I discovered that strftime was having none of those shenanigans and would just convert Feb 30 to Mar 1, so hey, good for you, little POSIX, for being resilient in the face of crap input. Totally unexpected!

* Ok, to be fair, one person noticed. One person.
** Please do not ask me about Easter.

time_t Hard Mode

jwz — Thu, 29 Feb 2024 16:04:09 +0000

Deborah Pickett:

Kazakhstan, which has not observed daylight saving for 20 years, is turning the clocks back at 0:00 on 1 March 2024, to 23:00 on leap day February 29 2024.
Definitely playing time zones on Hard Mode, Kazakhstan. Thanks for doing some QA on stacked edge cases for us all!

chx:

Right but it's not daylight savings, the change is permanent: Kazakhstan will change from using two time zones to observing only one time zone in the entire territory: UTC+5.

Previously, previously, previously, previously, previously, previously, previously.

Today in "Daylight Savings Chaos Monkey"

jwz — Sat, 17 Feb 2024 10:30:45 +0000

If you have backups but you have never tried to restore them, you do not have backups. This is true.

I made a MySQL oopsie, and tried to restore a table from my voluminous backups of same, and was met with:

Incorrect datetime value: '2004-04-04 02:24:55' for column ...

If you have guessed that April 4, 2004 was when Daylight Savings Time began, you get a sticker. Yup, mysqldump writes out a date that it cannot parse. 2:24 AM did not exist, it was 3:24 AM. But in 2024, mysqldump dumped that TIMESTAMP field as the string "2:24" anyway, for reasons that I am sure that someone is about to tell me are Right and Proper.

Hand-hacking 700MB files in Emacs really brings me back to the Lucid Common Lisp days of tweaking single bytes in an a.out file to see what made it stop loading.

Update: The most frustrating part about this is that I had recently switched my schemata to use TIMESTAMP instead of DATETIME to avoid exactly this kind of nonsense. As I covered earlier, TIMESTAMP represents a point in time, a time_t, but DATETIME is a sequence of contextless ASCII characters throwing up their hands and yelling "YOLO!" But even that didn't save me, because mysqldump writes out TIMESTAMP using the exact same stupid string representation that I stopped using DATETIME to avoid.

Previously, previously, previously, previously.

The time_t is now

jwz — Fri, 02 Feb 2024 21:17:37 +0000

Debian: 64-bit time_t transition in progress:

The goal of this transition is to ensure that 32-bit architectures in trixie (whether they are currently release architectures, or out of archive, etc) will be capable of handling current and future timestamps referring to times beyond 2038. [...] The implementation of this plan [...] involves mass-NMUs of > 1200 library packages to rename them for (presumed) ABI-breaking changes.

Here's a glibc roadmap of one possible solution, which sounds pretty sensible to me. It's not clear to me whether Debian is doing that, something else, or a combination.

Previously, previously, previously, previously, previously, previously.

Daylight "Savings", your biannual chaos monkey

jwz — Sun, 05 Nov 2023 18:33:23 +0000

In this, The Year Y2K Plus Twenty-Three, MySQL still can't represent times properly. I rediscover this just about every November.

Last night at 1:54 AM (the first one, by which I mean 1699174476) I updated a DATETIME column with "col = NOW()". So did it store 1699174476 in there? It fucking well did not:

SELECT col ... → 2023-11-05 01:54:36 SELECT UNIX_TIMESTAMP(col) ... → 1699178076

That's not 2023-11-05 01:54:36 PDT. that's 2023-11-05 01:54:36 PST, which is one hour later:

1699167600 = 2023-11-05 00:00:00 PDT 1699171200 = 2023-11-05 01:00:00 PDT 1699174476 = 2023-11-05 01:54:36 PDT ←

the first one

1699174740 = 2023-11-05 01:59:00 PDT 1699174800 = 2023-11-05 01:00:00 PST 1699178076 = 2023-11-05 01:54:36 PST ←

the second one

1699178400 = 2023-11-05 02:00:00 PST

Even the non-storage null transform is ambiguous:

SELECT UNIX_TIMESTAMP (FROM_UNIXTIME (1699174476)) → 1699178076

Also, your periodic reminder that we are closer to the Y2038 bug than the Y2K bug:

SELECT UNIX_TIMESTAMP("2038-01-18 19:14:07") → 2147483647; SELECT UNIX_TIMESTAMP("2038-01-18 19:14:08") → NULL; SELECT VERSION() → 10.5.18-MariaDB-log

Update:

Ok, because this post is likely to be a top hit for "DATETIME vs. TIMESTAMP" for years to come, and because there is some absolutely terrible advice and explanation out there, particularly on Sack Overflow, let me lay out what I have learned.

tl;dr -- never use DATETIME, always use TIMESTAMP.

TIMESTAMP is a time_t -- it represents an absolute, fixed point in time. Use it for things like "here is when this account was created" or "here is when this message was sent". When presenting that fixed point in time to users as text, you might want to format it in their local time zone.
DATETIME is basically a string of the wall clock in whatever time zone you happen to be in at the moment, without saving that time zone. It is ambiguous, e.g. it cannot represent "1:30 AM" on the day that daylight savings time ends because there are two of those on that day. This is never what you want.
DATE is a floating year-month-day. Use this for things like birthdays, which, by convention, do not change when you move halfway around the world.
TIME is a floating hour-minute-second. Use this for things like, "my alarm clock goes off at 9 AM regardless of what time zone I'm in, or if daylight savings time has flipped."

Downside to TIMESTAMP is that it (currently) can't represent dates after 2038 or before 1970. DATETIME can, but DATETIME is (I cannot emphasize this enough) garbage, so do not use it. For outlier dates, your options are:

Hope and pray that within the next few years, MySQL and MariaDB expand TIMESTAMP to 64 bits;
Use BIGINT instead and store a 64 bit time_t manually.

Extra stupidity! The TIMESTAMP type has some asinine defaults that differ from what anyone would expect. It defaults to:

NOT NULL DEFAULT CURRENT_TIMESTAMP() ON UPDATE CURRENT_TIMESTAMP()

and to avoid that, particularly to avoid getting fucked by that auto-update, you need to specify the column as either "timestamp NULL DEFAULT NULL" or as "NOT NULL DEFAULT 0".

It's a wonder anything works at all.

Previously, previously, previously, previously, previously, previously, previously, previously.

March Fourth. Fourth March.

jwz — Sat, 04 Mar 2023 19:36:26 +0000

The date is now Saturday, March 1,099th, 2020. The fourth March of the ongoing pandemic that is still killing more than 11,000 people a month in the US alone, and permanently disabling so many more. And still you assholes won't even consider masking.

If you choose to stand around inside a crowded room without wearing a mask -- I think you're a fucking idiot.

Turns out, nearly every person I know is a fucking idiot.

Sat Mar 1099 11:37:19 PST 2020

Here's what our calendar looked like in that first March, as we shut down for fourteen months.

And that March marches on.

Included amongst the aforementioned fucking idiots is a good friend who just contracted COVID for the THIRD time, who never wears a mask, ever. "What difference does it make?" she says. Then I cite studies showing what difference it makes. She shrugs it off with, "I can't keep living in fear".

To her, and to so many others, going to movie theatres and crowded nightclubs, but hanging a thin piece of plastic on their face while doing it, constitutes "living in fear".

No, we must pretend that the world has not changed in any material way since 2019. Those Eden-like pastoral days of 2019, before any of you had experienced "sadness" or "fear".

It would be bad enough if these people came upon their self-destructive and asinine positions naturally, but as with all the horrors of the modern world, this was not a choice, it was done to them by billionaires:

Lucky Tran:

These disinformation tactics are successfully quashing public health policies. Policymakers are susceptible to bad faith arguments about masks because they are beholden to short-term corporate interests. Masks are a visible symbol that the pandemic is ongoing, and politicians fear that these reminders stop people from consuming. It's easy to lie to those who want to believe.

An immunocompromised friend recently attended a funeral, and was repeatedly told by other maskless attendees how "brave" they were for masking. Brave?

"I don't really have a choice," they said.

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Time Slider

jwz — Mon, 27 Feb 2023 23:24:02 +0000

Time Slider

▶︎

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Y2038

jwz — Wed, 15 Feb 2023 22:09:07 +0000

Previously, previously, previously, previously, previously, previously, previously, previously.

The date is now Thursday, March 1069th, 2020.

jwz — Fri, 03 Feb 2023 03:10:02 +0000

Adam Daniel: I watched Groundhog Day every day for a year:

"What would you do if you were stuck in one place, and every day was exactly the same, and nothing that you did mattered?" [...]
In 2021 I was wrestling with the same question. Living in lockdown, I was feeling frustration, ennui, and like forward progress had ground to a halt. The circumstances created an opportunity to subject myself to a very unusual challenge: to watch the same film once a day, every day, for a year. [...]
I began to notice the reoccurrence of certain extras from scene to scene, building my own narrative around their identities. I realised the boy in a wheelchair in the background of the hospital scene is the same boy Phil will eventually save from breaking his leg every day. [...]
By the midway point, my viewing had shifted into a mode of cataloguing and memorisation. Phil Connors's weather reports ran through my head unbidden, and I had built myself a mental map of Punxsutawney to where I felt like I could give directions to a visitor. I began to talk to the film as it played.
Some days, the viewing felt like a curse. When Rita discovers Phil's dilemma, she says: "Maybe it's not a curse. Maybe it depends on how you look at it."

Previously, previously, previously, previously, previously.

Lunar Time

jwz — Sun, 29 Jan 2023 02:57:56 +0000

Not only do you need leap seconds to keep solar time and atomic time in sync, you'll need a different kind of leap second to keep Lunar atomic time and Earth atomic time in sync, because mass distorts spacetime.

So good luck with that...

Defining lunar time is not simple:

Although the definition of the second is the same everywhere, the special theory of relativity dictates that clocks tick slower in stronger gravitational fields. The Moon's gravitational pull is weaker than Earth's, meaning that, to an observer on Earth, a lunar clock would run faster than an Earth one. Gramling estimates that a lunar clock would gain about 56 microseconds over 24 hours. Compared with one on Earth, a clock's speed would also subtly change depending on its position on the lunar surface, because of the Moon's rotation, says Tavella. "This is a paradise for experts in relativity, because you have to take into account so many things," she adds.

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Great Moments in Taxonomy

jwz — Sun, 03 Apr 2022 23:41:55 +0000

Horrible edge cases to consider when dealing with music.

Pairs nicely with Falsehoods Programmers Believe About Names, Time, Time, Time Zones, Geography, Addresses, Maps, Plain Text, Gender, Lists.

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DST

jwz — Tue, 15 Mar 2022 23:14:34 +0000

Daylight Saving Time Gripe Assistant Tool

For this map I made up a score to prove that you're right (or wrong) about Daylight Saving Time ruining everything. It's the total number of days with both sunrise and sunset times that satisfy your preferences, minus a penalty for sunrise and sunset times that are too late or early, respectively.

Previously, previously, previously, previously, previously, previously, previously.

Y2038

jwz — Sun, 20 Feb 2022 16:18:27 +0000

Your periodic reminder that we are closer to the Y2038 bug than the Y2K bug:

SELECT UNIX_TIMESTAMP("2038-01-18 19:14:07") → 2147483647; SELECT UNIX_TIMESTAMP("2038-01-18 19:14:08") → NULL; SELECT VERSION() → 10.4.22-MariaDB-log

Previously, previously, previously, previously, previously.

The date is now Wednesday, March 704th, 2020.

jwz — Wed, 02 Feb 2022 17:47:23 +0000

Previously, previously, previously, previously.

202█

jwz — Fri, 31 Dec 2021 21:41:01 +0000

The date is now Friday, March 671st, 2020.

"Happy" "New" Year.

perl -e 'use Date::Parse; use POSIX; my @t = localtime; print strftime ("%a Mar ", @t) . int (1 + 0.5 + ((str2time (strftime ("%Y-%m-%d 3:00", @t)) - str2time ("2020-03-01 3:00")) /(60*60*24))) . strftime (" %X %Z 2020\n", @t);'

Fri Mar 671 13:41:08 PST 2020

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