2026-10-24 21:48 UTC
You've heard of Y2K and the 2038 problem, but what about the 1975 problem?
The UNIX form letter generator converts the current date to a string, but it only handles 1974. Why isn't it more general?
Well, the form utility was written around 1971 when UNIX used a different unit for time, jiffies (60ths of a second) since the current year instead of seconds since 1970. This 60× precision caused times to overflow a signed 32-bit integer every 13.6 months, so the epoch was bumped yearly. This yearly ritual of modifying the kernel meant it wasn't worth generalizing to support any year.
An earlier version of form uses jiffies since a 1972 epoch. The version from UNIX V4–V6 does the bare minimum to update it to the new system of seconds since 1970, while keeping the yearly overflow.
#unix #retrocomputing #vintagecomputing
Replies (4)
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@KaraLG84@dragonscave.space 2026-10-24 22:26
@thalia@discuss.systems Jiffies is an actual thing? I just thought it was a made up word.
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@bonkers@nerdculture.de 2026-10-26 07:13
@thalia@discuss.systems so, they built a groundhog year system before groundhogs were a thing
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@buherator@infosec.place 2026-10-26 08:08
@thalia@discuss.systems Someone must've been really proud of this Very Clever System. With jiffies.
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@captainarcee@retrochat.online 2026-10-26 14:55
@thalia@discuss.systems TIL Jiffy is a real unit of time measurement