semget(2)							     semget(2)

NAME    [Toc]    [Back]

     semget - get set of semaphores

SYNOPSIS    [Toc]    [Back]

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

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

DESCRIPTION    [Toc]    [Back]

     semget returns the	semaphore identifier associated	with key.

     A semaphore identifier and	associated data	structure and set containing
     nsems semaphores [see intro(2)] are created for key if one	of the
     following is true:

	  key is equal to IPC_PRIVATE.

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

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

	  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, respectively,
	  of the calling process.

	  The access permission	bits of	sem_perm.mode are set equal to the
	  access permission bits of semflg.

	  sem_nsems is set equal to the	value of nsems.

	  sem_otime is set equal to 0 and sem_ctime is set equal to the
	  current time.



     semget fails if one or more of the	following are true:

     EINVAL	    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 [see intro(2)] as specified by the low-order 9
		    bits of semflg would not be	granted.

     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.




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semget(2)							     semget(2)



     ENOENT	    A semaphore	identifier does	not exist for key and
		    (semflg<b>&IPC_CREAT) is false.

     ENOSPC	    A semaphore	identifier is to be created but	the systemimposed
 limit on the maximum number	of allowed semaphore
		    identifiers	system wide would be exceeded.

     ENOSPC	    A semaphore	identifier is to be created but	the systemimposed
 limit on the maximum number	of allowed semaphores
		    system wide	would be exceeded.

     EEXIST	    A semaphore	identifier exists for key but both
		    (semflg<b>&IPC_CREAT) and (semflg<b>&IPC_EXCL) are both true.

SEE ALSO    [Toc]    [Back]

     intro(2), semctl(2), semop(2), stdipc(3C).

DIAGNOSTICS    [Toc]    [Back]

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


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