sys_un.h(7POSIX)

📦 version 2017a, in debian bookworm, debian trixie, ubuntu jammy, ubuntu noble, ubuntu resolute, ubuntu stonking

💖 sys_un.h — the POSIX tea, bestie edition 💖

okay so real quick, this is sys_un.h(7POSIX), straight outta the POSIX Programmer's Manual, and I'm gonna walk you through it like we're texting at 2am 🦋

✨ PROLOG ✨

okay bestie, ground rules first 👑

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, consult the corresponding Linux manual page for details of Linux behavior — or honestly the interface may not even be implemented on Linux at all. 😭 vibe check failed, sorry.

🌸 NAME 🌸

sys/un.h — definitions for UNIX domain sockets. iconic behavior, no notes 💅

✨ SYNOPSIS ✨

#include <sys/un.h>

that's it. that's the whole synopsis. she's low maintenance ✨

🎀 DESCRIPTION 🎀

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

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

The sockaddr_un structure is what you use to store addresses for UNIX domain sockets. Pointers to this type shall be cast by applications to struct sockaddr * for use with socket functions — yes, that cast, you know the one 🫶

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, cute to know, but not the law 📜

🌈 APPLICATION USAGE 🌈

okay so the size of sun_path has intentionally been left undefined. not an oversight, it's giving on purpose 💅 and the reason is that different implementations use different sizes. for example:

  • 4.3 BSD uses a size of 108
  • 4.4 BSD uses a size of 104

and since most implementations originate from BSD versions, the size is typically in the range 92 to 108.

Applications should not assume a particular length for sun_path, and should not assume that it can hold {_POSIX_PATH_MAX} bytes (that's 256, bestie). 🚨

Now, here's a lil plot twist 😳 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, since 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 it for the plot, do it for the culture 🧚

💜 RATIONALE 💜

None. she said nothing, your honor 💀

🦋 FUTURE DIRECTIONS 🦋

None. the future is cancelled apparently 🫶

⭐ SEE ALSO ⭐

  • <netinet_in.h>
  • <sys_socket.h>

The System Interfaces volume of POSIX.1‐2017: bind(), socket(), socketpair() — go read those next, they're the main characters of this whole saga 👑

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 .

and that's the whole page, bestie 🎀 this was IEEE/The Open Group, 2017, sys_un.h(7POSIX) — mwah, go touch some sockets 💖✨🌸

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