SEMGET(2)                            SysV                            SEMGET(2)



NAME
     semget - get set of semaphores

SYNOPSIS
     #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 associated with it,
        and (semflg & IPC_CREAT) is "true".

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

     1.  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.

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

     3.  sem_nsems is set equal to the value of nsems.

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

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

     [EINVAL]   nsems is either less than or equal to 0 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 nine
                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 0.

     [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
                system wide would be exceeded.

     [ENOSPC]   A semaphore identifier is to be created but the system-imposed

                limit on the maximum number of allowed semaphores system wide
                would be exceeded.

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

SEE ALSO
     intro(2), semctl(2), semop(2).

DIAGNOSTICS
     Upon successful completion, a non-negative integer, namely a semaphore
     identifier, is returned.  Otherwise, a value of -1 is returned and errno
     is set as indicated under "Errors."