SHM_UNLINK(3P) POSIX Programmer's Manual SHM_UNLINK(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.

shm_unlink — remove a shared memory object (REALTIME)

#include <sys/mman.h>
int shm_unlink(const char *name);

The shm_unlink() function shall remove the name of the shared memory object named by the string pointed to by name.

If one or more references to the shared memory object exist when the object is unlinked, the name shall be removed before shm_unlink() returns, but the removal of the memory object contents shall be postponed until all open and map references to the shared memory object have been removed.

Even if the object continues to exist after the last shm_unlink(), reuse of the name shall subsequently cause shm_open() to behave as if no shared memory object of this name exists (that is, shm_open() will fail if O_CREAT is not set, or will create a new shared memory object if O_CREAT is set).

Upon successful completion, a value of zero shall be returned. Otherwise, a value of -1 shall be returned and errno set to indicate the error. If -1 is returned, the named shared memory object shall not be changed by this function call.

The shm_unlink() function shall fail if:

Permission is denied to unlink the named shared memory object.
The named shared memory object does not exist.

The shm_unlink() function may fail if:

The length of the name argument exceeds {_POSIX_PATH_MAX} on systems that do not support the XSI option or exceeds {_XOPEN_PATH_MAX} on XSI systems, or has a pathname component that is longer than {_POSIX_NAME_MAX} on systems that do not support the XSI option or longer than {_XOPEN_NAME_MAX} on XSI systems. A call to shm_unlink() with a name argument that contains the same shared memory object name as was previously used in a successful shm_open() call shall not give an [ENAMETOOLONG] error.

The following sections are informative.


Names of memory objects that were allocated with open() are deleted with unlink() in the usual fashion. Names of memory objects that were allocated with shm_open() are deleted with shm_unlink(). Note that the actual memory object is not destroyed until the last close and unmap on it have occurred if it was already in use.


A future version might require the shm_open() and shm_unlink() functions to have semantics similar to normal file system operations.

close(), mmap(), munmap(), shmat(), shmctl(), shmdt(), shm_open()

The Base Definitions volume of POSIX.1‐2017, <sys_mman.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