semget(2) [netbsd man page]

SEMGET(2)						      BSD System Calls Manual							 SEMGET(2)

NAME

     semget -- get set of semaphores

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/sem.h>

     int
     semget(key_t key, int nsems, int semflg);

DESCRIPTION

     The semget() system call returns the semaphore identifier associated with key.

     A new set containing nsems semaphores is created if either key is equal to IPC_PRIVATE, or key does not have a semaphore set associated with
     it and the IPC_CREAT bit is set in semflg.  If both the IPC_CREAT bit and the IPC_EXCL bit are set in semflg, and key has a semaphore set
     associated with it already, the operation will fail.

     If a new set of semaphores is created, the data structure associated with it (the semid_ds structure, see semctl(2)) is initialized as fol-
     lows:

     o	 sem_perm.cuid and sem_perm.uid are set to the effective uid of the calling process.

     o	 sem_perm.gid and sem_perm.cgid are set to the effective gid of the calling process.

     o	 sem_perm.mode is set to the lower 9 bits of semflg.

     o	 sem_nsems is set to the value of nsems.

     o	 sem_ctime is set to the current time.

     o	 sem_otime is set to 0.

RETURN VALUES

     semget() returns a non-negative semaphore identifier if successful.  Otherwise, -1 is returned and errno is set to reflect the error.

ERRORS

     [EACCES]		The caller has no permission to access a semaphore set already associated with key.

     [EEXIST]		Both IPC_CREAT and IPC_EXCL are set in semflg, and a semaphore set is already associated with key.

     [EINVAL]		nsems is less than 0 or greater than the system limit for the number in a semaphore set.

			A semaphore set associated with key exists, but has fewer semaphores than the number specified in nsems.

     [ENOSPC]		A new set of semaphores could not be created because the system limit for the number of semaphores or the number of sema-
			phore sets has been reached.

     [ENOENT]		IPC_CREAT is not set in semflg and no semaphore set associated with key was found.

SEE ALSO

     ipcs(1), semctl(2), semop(2), ftok(3)

STANDARDS

     The semget system call conforms to X/Open System Interfaces and Headers Issue 5 (``XSH5'').

HISTORY

     Semaphores appeared in the first release of AT&T System V UNIX.

BSD
								   May 13, 2004 							       BSD

semget(2)							System Calls Manual							 semget(2)

Name
       semget - get set of semaphores

Syntax
       #include <sys/types.h>
       #include <sys/ipc.h>
       #include <sys/sem.h>

       int semget (key, nsems, semflg)
       key_t key;
       int nsems, semflg;

Description
       The  system  call  returns the semaphore identifier associated with key.  A semaphore identifier and associated data structure and set con-
       taining nsems semaphores are created for key, if one of the following is true:

       o   The key is equal to IPC_PRIVATE

       o   The key does not already have a semaphore identifier associated with it, and (semflg & IPC_CREAT ) is true.

       For further information, see

       Upon creation, the data structure associated with the new semaphore identifier is initialized as follows:

       o   The sem_perm.cuid, sem_perm.uid, sem_perm.cgid and sem_perm.gid are set equal to the effective user ID and effective group ID,  respec-
	   tively, of the calling process.

       o   The low-order nine bits of sem_perm.mode are set equal to the low-order nine bits of semflg.

       o   The sem_nsems is set equal to the value of nsems.

       o   The sem_otime is set equal to zero (0) and sem_ctime is set equal to the current time.

Return Values
       Upon  successful  completion,  a nonnegative integer, namely a semaphore identifier, is returned.  Otherwise, a value of -1 is returned and
       errno is set to indicate the error.

Diagnostics
       The semget system call fails if any of the following is true:

       [EINVAL]       The nsems is either less than or equal to zero or greater than the system-imposed limit

       [EACCES]       A semaphore identifier exists for key, but operation permission, as specified by the low-order nine bits of semflg would not
		      be granted.  For further information, see

       [EINVAL]       A  semaphore  identifier	exists	for key, but the number of semaphores in the set associated with it is less than nsems and
		      nsems is not equal to zero.

       [ENOENT]       A semaphore identifier does not exist for key and (semflg & IPC_CREAT ) is false.

       [ENOSPC]       A semaphore identifier is to be created but the system-imposed limit on the maximum number of allowed semaphore  identifiers
		      in the system would be exceeded.

       [EEXIST]       A semaphore identifier exists for key but ((semflg & IPC_CREAT ) & (semflg & IPC_EXCL )) is true.

See Also
       semctl(2), semop(2), ftok(3)

																	 semget(2)