sys_sem.h(7POSIX) POSIX Programmer's Manual sys_sem.h(7POSIX)
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.
sys/sem.h — XSI semaphore facility
The <sys/sem.h> header shall define the following symbolic constant for use as a semaphore
SEM_UNDO Set up adjust on exit entry.
The <sys/sem.h> header shall define the following symbolic constants for use as commands
for the semctl() function:
GETNCNT Get semncnt.
GETPID Get sempid.
GETVAL Get semval.
GETALL Get all cases of semval.
GETZCNT Get semzcnt.
SETVAL Set semval.
SETALL Set all cases of semval.
The <sys/sem.h> header shall define the semid_ds structure, which shall include the fol‐
struct ipc_perm sem_perm Operation permission structure.
unsigned short sem_nsems Number of semaphores in set.
time_t sem_otime Last semop() time.
time_t sem_ctime Last time changed by semctl().
The <sys/sem.h> header shall define the pid_t, size_t, and time_t types as described in
A semaphore shall be represented by an anonymous structure, which shall include the fol‐
unsigned short semval Semaphore value.
pid_t sempid Process ID of last operation.
unsigned short semncnt Number of processes waiting for semval
to become greater than current value.
unsigned short semzcnt Number of processes waiting for semval
to become 0.
The <sys/sem.h> header shall define the sembuf structure, which shall include the follow‐
unsigned short sem_num Semaphore number.
short sem_op Semaphore operation.
short sem_flg Operation flags.
The following shall be declared as functions and may also be defined as macros. Function
prototypes shall be provided.
int semctl(int, int, int, ...);
int semget(key_t, int, int);
int semop(int, struct sembuf *, size_t);
In addition, the <sys/sem.h> header shall include the <sys/ipc.h> header.
The following sections are informative.
The System Interfaces volume of POSIX.1‐2008, semctl(), semget(), semop()
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrep‐
ancy 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely to have
been introduced during the conversion of the source files to man page format. To report
such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 sys_sem.h(7POSIX)