SHMDT(3P) POSIX Programmer's Manual SHMDT(3P)

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

shmdt — XSI shared memory detach operation

#include <sys/shm.h>
int shmdt(const void *shmaddr);

The shmdt() function operates on XSI shared memory (see the Base Definitions volume of POSIX.1‐2017, Section 3.346, Shared Memory Object). It is unspecified whether this function interoperates with the realtime interprocess communication facilities defined in Section 2.8, Realtime.

The shmdt() function detaches the shared memory segment located at the address specified by shmaddr from the address space of the calling process.

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.

Otherwise, the shared memory segment shall not be detached, shmdt() shall return -1, and errno shall be set to indicate the error.

The shmdt() function shall fail if:

The value of shmaddr is not the data segment start address of a shared memory segment.

The following sections are informative.


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.



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>

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 .

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2017 IEEE/The Open Group