SHMDT(3POSIX)

SHMDT(3POSIX) 💅

okay bestie, welcome to the POSIX Programmer's Manual ✨ this one's about shmdt, and yes it's giving "detach that shared memory segment, queen." let's go 🫶

---

🌸 PROLOG 🌸

so, real talk: this manual page is part of the POSIX Programmer's Manual. the Linux implementation of this interface may differ (so go consult the corresponding Linux manual page for the details of Linux behavior, fr), or honestly the interface may not be implemented on Linux at all. not me warning you up front 💀

---

✨ NAME ✨

shmdt — XSI shared memory detach operation 🎀

---

🦋 SYNOPSIS 🦋

#include <sys/shm.h>

int shmdt(const void *shmaddr);

---

💖 DESCRIPTION 💖

so shmdt() operates on XSI shared memory (peep the Base Definitions volume of POSIX.1‐2017, Section 3.346, Shared Memory Object for the lore 👑).

and listen — it is unspecified whether this function interoperates with the realtime interprocess communication facilities defined in Section 2.8, Realtime. like, nobody's promising that, bestie 🙈

what shmdt() actually does: it detaches the shared memory segment located at the address specified by shmaddr from the address space of the calling process. it's the "and we are SO done here" of memory management 🧚

---

🌈 RETURN VALUE 🌈

upon successful completion, shmdt() shall:

• decrement the value of shm_nattch in the data structure associated with the shared memory ID of the attached shared memory segment, and
• return 0.

also — the shm_dtime timestamp shall be set to the current time, as described in Section 2.7.1, IPC General Description. clocking the departure, iconic ⭐

otherwise? the shared memory segment shall not be detached, shmdt() shall return -1, and errno shall be set to indicate the error. it's giving "nope, didn't happen" 💀

---

👑 ERRORS 👑

the shmdt() function shall fail if:

• EINVAL — the value of shmaddr is not the data segment start address of a shared memory segment. like, that's not the address, babe 😭

the following sections are informative.

---

🎀 EXAMPLES 🎀

None.

(yeah. nothing. empty. the void. not a single example, and that's just how it is 🙈)

---

🌸 APPLICATION USAGE 🌸

so the POSIX Realtime Extension defines alternative interfaces for interprocess communication. application developers who need to use IPC should design their applications so that modules using the IPC routines described in Section 2.7, XSI Interprocess Communication can be easily modified to use the alternative interfaces. future-proof your code, bestie, it's the move 💜

---

🦋 RATIONALE 🦋

None.

---

⭐ FUTURE DIRECTIONS ⭐

None.

---

🔥 SEE ALSO 🔥

• Section 2.7, XSI Interprocess Communication
• Section 2.8, Realtime
• exec
• exit()
• fork()
• shmat()
• shmctl()
• shmget()
• shm_open()
• shm_unlink()
• the Base Definitions volume of POSIX.1‐2017, Section 3.346, Shared Memory Object
• <sys_shm.h>

---

💜 COPYRIGHT 💜

okay legal girlies, this part stays exactly as-is, no vibes applied, because it's the law 📜:

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 one came to you from IEEE/The Open Group, dated 2017, and it lives under the name SHMDT(3POSIX). slay, stay detached, and go touch some shared memory 💅✨