shmdt man page


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.1‐2008, Section 3.342, 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.

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.

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.

Application Usage

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.

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.1‐2008, Section 3.342, Shared Memory Object, <sys_shm.h>