The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
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shm_unlink - remove a shared memory object (REALTIME)


[SHM] [Option Start] #include <sys/mman.h>

int shm_unlink(const char *
name); [Option End]


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 length of the name argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.
The named shared memory object does not exist.

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.






close(), mmap(), munmap(), shmat(), shmctl(), shmdt(), shm_open(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/mman.h>


First released in Issue 5. Included for alignment with the POSIX Realtime Extension.

Issue 6

The shm_unlink() function is marked as part of the Shared Memory Objects option.

In the DESCRIPTION, text is added to clarify that reusing the same name after a shm_unlink() will not attach to the old shared memory object.

The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Shared Memory Objects option.

End of informative text.

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