socketpair(2)

💖 socketpair(2) 💖

okay bestie, pull up a chair, we're doing the System Calls Manual thing and this one is genuinely so cute. it's socketpair(2) and it lives in the System Calls Manual, which is exactly where you'd expect a syscall to be hiding. no cap.

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✨ NAME ✨

socketpair — create a pair of connected sockets 🫶

📚 LIBRARY 📚

Standard C library (libc, -lc). she's in libc, she's always been in libc.

🎀 SYNOPSIS 🎀

#include <sys/socket.h>

int socketpair(int domain, int type, int protocol, int sv[2]);

🦋 DESCRIPTION 🦋

so the socketpair() call creates an unnamed pair of connected sockets. like, two sockets. joined. bestie-coded. 💅

and you get to pick:

• the domain — the specified domain she lives in
• the type — the specified type, obviously
• the protocol — optionally specified, so it's giving "only if you want to"

want the full lore on these three arguments? they're not doing a solo performance here, go read socket(2). ✨

the file descriptors you use to reference your brand-new sockets get returned in sv[0] and sv[1]. and here's the iconic part: the two sockets are indistinguishable. twin flames. main character energy, doubled. you cannot tell them apart, that is the whole point, periodt. 👑

🔥 RETURN VALUE 🔥

• on success: zero is returned. slay.
• on error: -1 is returned, errno is set to indicate the error, and sv is left unchanged.

and bestie, listen, this part matters: on Linux (and other systems), socketpair() does not modify sv on failure. a requirement standardizing this behavior was added in POSIX.1-2008 TC2. so your buffer stays pristine, no half-written chaos, we love a clean failure. 😭

💀 ERRORS 💀

• EAFNOSUPPORT — the specified address family is not supported on this machine. wrong vibe, wrong house, sorry babe.
• EFAULT — the address sv does not specify a valid part of the process address space. that pointer is NOT it.
• EMFILE — the per-process limit on the number of open file descriptors has been reached. you personally have too many tabs open, metaphorically.
• ENFILE — the system-wide limit on the total number of open files has been reached. it's not you, it's literally everyone.
• EOPNOTSUPP — the specified protocol does not support creation of socket pairs. this protocol is not a matchmaker, she does not do pairings.
• EPROTONOSUPPORT — the specified protocol is not supported on this machine. nope, not here, not today.

🌸 VERSIONS 🌸

on Linux, the only supported domains for this call are AF_UNIX (or synonymously, AF_LOCAL) and AF_TIPC (since Linux 4.12). that's the whole list, bestie, don't go inventing more. 🎀

⭐ STANDARDS ⭐

POSIX.1-2024. certified, standard, official.

🌈 HISTORY 🌈

POSIX.1-2001, 4.2BSD. she's been around, she's a legacy icon.

it is generally portable to/from non-BSD systems supporting clones of the BSD socket layer (including System V variants). so she travels well, iykyk. 🧚

SOCK_CLOEXEC SOCK_NONBLOCK

• POSIX.1-2024; Linux 2.6.27. (See socket(2).)

👑 SEE ALSO 👑

pipe(2), read(2), socket(2), write(2), socket(7), unix(7)

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okay that's the whole page, go make some socket pairs, and remember: do not try to tell sv[0] and sv[1] apart because you literally cannot, and that's the beautiful part. 💖

this has been Linux man-pages 6.20, dated 2025-10-29, signing off like the absolute queen she is. bye bestie, drink water, close your file descriptors. 🌸✨💜