semget(2)                                                            semget(2)


NAME
     semget - get set of semaphores

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

     int semget(key_t key, int nsems, int 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.

     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.


     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 both
                    (semflg&IPC_CREAT) and (semflg&IPC_EXCL) are both true.

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

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 to indicate the error.


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