futex(9)

💖 futex(9) — from the Kernel API Manual, bestie 💖

okay so first things first: this is futex(9) straight out of the Kernel API Manual, and it's literally the low-level glue that every other futex wrapper in this little family sits on top of. buckle up 🎀

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✨ NAME ✨

futex — the SYS_futex syscall wrapper. that's it. that's the whole vibe. 🦋

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🌸 SYNOPSIS 🌸

futex (uaddr , op , val , timeout , uaddr2 , val3 , opflags );

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🎀 ARGUMENTS 🎀

• uaddr — the address of the first futex. like, the actual thing we're futexing about. 📍
• op — the futex op code. this tells everybody what we're doing here.
• val — typically the expected value of uaddr, but ngl it varies by op. it's giving "depends on context" 💅
• timeout — typically an absolute struct timespec (except where noted otherwise 👀). some ops overload this one and use it for something else entirely.
• uaddr2 — the address of the second futex, for the ops that need two. two futexes, double the fun 🫶
• val3 — varies by op. mystery girl behavior, honestly. 🙈
• opflags — flags you bitwise OR into op, such as FUTEX_PRIVATE_FLAG. stack 'em on top 🔥

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⭐ DESCRIPTION ⭐

so futex is the one all the following futex op wrappers are built on. every single one. it's the main character and the rest of them are the ensemble cast 👑

it can also be used for misuse and abuse testing, which, ok, iconic 😭 but generally you should reach for the specific op wrappers instead of this one. they exist for a reason, bestie.

the way that it's a macro and not a static inline function? that's because some of the types are overloaded — timeout gets used for nr_requeue, for example. so it literally cannot just be a normal function. no cap. 💀

and here's the important bit: all those argument descriptions up there are the defaults for every like-named argument in the following wrappers, except where noted below. so when you see uaddr or timeout in a wrapper manpage, assume it means what it meant here unless it says otherwise. 🧚

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🌈 SEE ALSO 🌈

• Kernel file ./tools/testing/selftests/futex/include/futextest.h — go read the source, it's right there 💜
• futex_wait(9)
• futex_wake(9)
• futex_wait_bitset(9)
• futex_wake_bitset(9)
• futex_lock_pi(9)
• futex_unlock_pi(9)
• futex_wake_op(9)
• futex_requeue(9)
• futex_cmp_requeue(9)
• futex_wait_requeue_pi(9)
• futex_cmp_requeue_pi(9)
• futex_cmpxchg(9)
• futex_dec(9)
• futex_inc(9)
• futex_set(9)

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lowkey a whole friend group of manpages. go say hi to all of them. 🌸

and that's the whole page, bestie!! source is ./tools/testing/selftests/fute... and it's dated October 2026 — so it's from the future, obviously, slay ⭐💅🦋