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_close — close a named semaphore
int sem_close(sem_t *sem);
The sem_close() function shall indicate that the calling process is
finished using the named semaphore indicated by sem. The effects of
calling sem_close() for an unnamed semaphore (one created by
sem_init()) are undefined. The sem_close() function shall
deallocate (that is, make available for reuse by a subsequent
sem_open() by this process) any system resources allocated by the
system for use by this process for this semaphore. The effect of subsequent
use of the semaphore indicated by sem by this process is undefined. If
any threads in the calling process are currently blocked on the semaphore, the
behavior is undefined. If the semaphore has not been removed with a successful
call to sem_unlink(), then sem_close() has no effect on the
state of the semaphore. If the sem_unlink() function has been
successfully invoked for name after the most recent call to
sem_open() with O_CREAT for this semaphore, then when all processes
that have opened the semaphore close it, the semaphore is no longer
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.
The sem_close() function may fail if:
- The sem argument is not a valid semaphore descriptor.
The following sections are informative.
semctl(), semget(), semop(),
sem_init(), sem_open(), sem_unlink()
The Base Definitions volume of POSIX.1‐2017,
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 http://www.opengroup.org/unix/online.html .
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