sem_unlink 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.

sem_unlink — remove a named semaphore


#include <semaphore.h>

int sem_unlink(const char *name);


The sem_unlink() function shall remove the semaphore named by the string name. If the semaphore named by name is currently referenced by other processes, then sem_unlink() shall have no effect on the state of the semaphore. If one or more processes have the semaphore open when sem_unlink() is called, destruction of the semaphore is postponed until all references to the semaphore have been destroyed by calls to sem_close(), _exit(), or exec. Calls to sem_open() to recreate or reconnect to the semaphore refer to a new semaphore after sem_unlink() is called. The sem_unlink() call shall not block until all references have been destroyed; it shall return immediately.

Return Value

Upon successful completion, the sem_unlink() function shall return a value of 0. Otherwise, the semaphore shall not be changed and the function shall return a value of -1 and set errno to indicate the error.


The sem_unlink() function shall fail if:

Permission is denied to unlink the named semaphore.
The named semaphore does not exist.

The sem_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 sem_unlink() with a name argument that contains the same semaphore name as was previously used in a successful sem_open() call shall not give an [ENAMETOOLONG] error.

The following sections are informative.

Future Directions

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

See Also

semctl(), semget(), semop(), sem_close(), sem_open()

The Base Definitions volume of POSIX.1‐2008, <semaphore.h>