PROLOG

       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.

NAME

       sys/sem.h — XSI semaphore facility

SYNOPSIS

       #include <sys/sem.h>

DESCRIPTION

       The  <sys/sem.h>  header  shall  define  the following symbolic constant for use as a semaphore operation
       flag:

       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 following members:

           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 <sys/types.h>.

       A semaphore shall be represented by an anonymous structure, which shall include the following members:

           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 following members:

           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.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       <sys_ipc.h>, <sys_types.h>

       The System Interfaces volume of POSIX.1‐2017, semctl(), semget(), semop()

COPYRIGHT

       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 .

       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 .