The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> shm_unlink - remove a shared memory object (REALTIME)

#### SYNOPSIS

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

#### DESCRIPTION

> 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).

#### RETURN VALUE

> 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.

#### ERRORS

> The shm_unlink() function shall fail if:

> [EACCES]
>   Permission is denied to unlink the named shared memory object.
> [ENOENT]
>   The named shared memory object does not exist.

> The shm_unlink() function may fail if:

> [ENAMETOOLONG]
>   The length of the name argument exceeds {_POSIX_PATH_MAX} on systems that do not support the XSI option [XSI] 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 [XSI] 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.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> 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.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

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

#### SEE ALSO

> close, mmap, munmap, shmat, shmctl, shmdt, shm_open

> XBD <sys/mman.h>

#### CHANGE HISTORY

> 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.

#### Issue 7

> Austin Group Interpretation 1003.1-2001 #077 is applied, changing [ENAMETOOLONG] from a ``shall fail'' to a ``may fail'' error.

> Austin Group Interpretation 1003.1-2001 #141 is applied, adding FUTURE DIRECTIONS.

End of informative text.

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