sys_un.h(0P)

💖 PROLOG 💖

okay so bestie, real talk before we even start: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ — so if you're on Linux, go consult the corresponding Linux manual page for the deets on how Linux actually does it. OR, plot twist, the interface might just not be implemented on Linux at all. 🙈

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✨ NAME ✨

sys/un.h — definitions for UNIX domain sockets 🦋

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🌸 SYNOPSIS 🌸

#include <sys/un.h>

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💅 DESCRIPTION 💅

So the <sys/un.h> header shall define the sockaddr_un structure, and that structure shall include at least these members:

sa_family_t  sun_family  Address family.
char         sun_path[]  Socket pathname.

The sockaddr_un structure is what stores addresses for UNIX domain sockets, periodt. And heads up: pointers to this type shall be cast by applications to struct sockaddr * when you use them with socket functions. iykyk 🔥

Also the <sys/un.h> header shall define the sa_family_t type as described in <sys/socket.h>.

The following sections are informative. (so like, the juicy bits, not the binding law — noted 📝)

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🎀 APPLICATION USAGE 🎀

Not me about to explain why sun_path is so mysterious…

The size of sun_path has intentionally been left undefined. Why? Because different implementations use different sizes, bestie. For example, 4.3 BSD uses a size of 108, and 4.4 BSD uses a size of 104. Since most implementations originate from BSD versions, the size is typically in the range 92 to 108.

So applications should not assume a particular length for sun_path, and should not assume that it can hold {_POSIX_PATH_MAX} bytes (256). Don't do it. It's giving chaos. 💀

Now here's a lil comparison that lowkey matters: applications are required to initialize all members (including any non-standard ones) of a sockaddr_in6 structure (see <netinet_in.h>), but the same is not required for the sockaddr_un structure — because historically, many applications only initialized the standard members. Despite this, applications are encouraged to initialize sockaddr_un structures in a manner similar to the required initialization of sockaddr_in6 structures. Do the extra credit, bestie, it's cute. 🫶

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🧚 RATIONALE 🧚

None.

(yes, literally none. iconic behavior honestly 👑)

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🌈 FUTURE DIRECTIONS 🌈

None.

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⭐ SEE ALSO ⭐

• <netinet_in.h>
• <sys_socket.h>
• The System Interfaces volume of POSIX.1‐2017, bind(), socket(), socketpair()

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👑 COPYRIGHT 👑

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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k that's the whole page, no cap 💖 stay safe out there and initialize your structs 🦋

IEEE/The Open Group 🌸 2017 ✨ sys_un.h(0P) 🎀 — mwah, bye bestie! 💅