SEMGET(2)                DOMAIN/IX SYS5                 SEMGET(2)



NAME
     semget - get set of semaphores

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

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


DESCRIPTION
     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 associ-
        ated with it, and

          (semflg & IPC_CREAT)

        is "true".

     Upon 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 low-order 9 bits of sem_perm.mode are set equal to
        the low-order 9 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.

RETURN VALUE
     A successful semget returns a non-negative integer semaphore
     identifier upon completion.  A failed call returns -1 and
     sets errno as indicated below.





Printed 12/4/86                                          SEMGET-1

SEMGET(2)                DOMAIN/IX SYS5                 SEMGET(2)



ERRORS
     Semget will fail if one or more of the following is 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 opera-
               tion permission (see intro(2)) as specified by the
               low-order 9 bits of semflg cannot 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.

     [ENOENT]  A semaphore identifier does not exist for key and

                 (semflg & IPC_CREAT)

               is "false".

     [ENOSPC]  Creating a new semaphore identifier would exceed
               the system-imposed limit on the maximum number of
               semaphore identifiers allowed on the system.

     [EEXIST]  A semaphore identifier exists for key but

                 ((semflg & IPC_CREAT) & (semflg & IPC_EXCL))

               is "true".

RELATED INFORMATION
     semctl(2), semop(2)





















SEMGET-2                                          Printed 12/4/86