wait4(2)

💖 wait4(2) — the BSD-style "wait for your child to change state" page 💖

okay bestie, pull up a chair, we're in the System Calls Manual and this one is a whole mood. it's wait3 and wait4, the BSD-style girlies. ✨

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🎀 NAME 🎀

wait3, wait4 — wait for process to change state, BSD style

no cap, that's literally it. they wait, and they're BSD-flavored. 💅

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📚 LIBRARY 📚

Standard C library (libc, -lc)

yes girl, that's the library. you already link it in basically everything. 🫶

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✨ SYNOPSIS ✨

#include <sys/wait.h>

pid_t wait3(int *_Nullable wstatus, int options,
            struct rusage *_Nullable rusage);
pid_t wait4(pid_t pid, int *_Nullable wstatus, int options,
            struct rusage *_Nullable rusage);

🦋 Feature Test Macro Requirements for glibc (see feature_test_macros(7)): 🦋

listen, this part is giving "bureaucracy" but it's important, so here it is in all its glory:

wait3():
    Since glibc 2.26:
        _DEFAULT_SOURCE
            || (_XOPEN_SOURCE >= 500 &&
                ! (_POSIX_C_SOURCE >= 200112L
                   || _XOPEN_SOURCE >= 600))
    From glibc 2.19 to glibc 2.25:
        _DEFAULT_SOURCE || _XOPEN_SOURCE >= 500
    glibc 2.19 and earlier:
        _BSD_SOURCE || _XOPEN_SOURCE >= 500

wait4():
    Since glibc 2.19:
        _DEFAULT_SOURCE
    glibc 2.19 and earlier:
        _BSD_SOURCE

if you forget these, the compiler will be like "who?" and you'll be sad. 😭

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🌸 DESCRIPTION 🌸

first things first, and I need you to hear me on this: these functions are nonstandard. in new programs, using waitpid(2) or waitid(2) is preferable. like, it's not a scandal, they're just old money and we have better options now. 💜

so what do they even do? the wait3() and wait4() system calls are similar to waitpid(2), BUT — and this is their little extra sparkle — they additionally return resource usage information about the child in the structure pointed to by rusage. it's giving "waiting, but make it informative". 👑

other than the rusage argument being a whole extra thing, this wait3() call:

wait3(wstatus, options, rusage);

is equivalent to:

waitpid(-1, wstatus, options);

and similarly, this wait4() call:

wait4(pid, wstatus, options, rusage);

is equivalent to:

waitpid(pid, wstatus, options);

in other words (and this is the vibe check you needed):

• wait3() waits for any child 🌈
• wait4() can be used to select a specific child, or children, on which to wait

see wait(2) for further details, bestie, that's where the deep lore lives. 📖

and if rusage is not NULL, the struct rusage it points to will be filled with accounting information about the child. again: see getrusage(2) for details. it's all connected, iykyk. ✨

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🔥 RETURN VALUE 🔥

As for waitpid(2).

(that's the whole section. short king. respect.) 💀

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💀 ERRORS 💀

As for waitpid(2).

(same energy. we don't reproduce them here, we send you to the source.) 🙈

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📜 STANDARDS 📜

None.

literally none. zero. it's a lone wolf. not standard anywhere. periodt. 💅

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⭐ HISTORY ⭐

4.3BSD.

the timeline, because we love a documented glow-up:

• SUSv1 included a specification of wait3()
• SUSv2 included wait3(), but marked it LEGACY (oof, the shade 😭)
• SUSv3 removed it

also, tea time: including <sys/time.h> is not required these days, but it increases portability. (indeed — and this is the receipts, bestie — <sys/resource.h> defines the rusage structure with fields of type struct timeval defined in <sys/time.h>.) so it's optional but it's kind of a considerate move. 🎀

🧚 C library/kernel differences 🧚

on Linux, wait3() is a library function implemented on top of the wait4() system call. so yes, wait3 is basically wait4's little sibling borrowing her outfit. iconic behavior fr fr. 💖

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👑 SEE ALSO 👑

fork(2), getrusage(2), sigaction(2), signal(2), wait(2), signal(7)

go read these too, they're the group chat and this page is just one message in it. 🦋

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and that's the whole page, bestie!! this one shipped from Linux man-pages 6.20, dated 2026-02-08. now go reap your zombies before they start texting you passive-aggressively. mwah. 💅✨🎀🫶