Description

   The semget function returns the semaphore identifier associated
   with key.

   A semaphore identifier with its associated semid_ds data
   structure and its associated set of nsems semaphores (see
   the <sys/sem.h> header file) is created for key if one of the
   following is true:

   o  The key argument is equal to IPC_PRIVATE.

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

   When it is created, the semid_ds data structure associated with
   the new semaphore identifier is initialized as follows:

   o  In the operation permissions structure 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.

   o  The low-order 9 bits of sem_perm.mode are set equal to the
      low-order 9 bits of the semflg argument.

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

   o  The variable sem_otime is set equal to 0 and the variable sem_
      ctime is set equal to the current time.

   o  The data structure associated with each semaphore in the
      set does not need to be initialized. You can use the semctl
      function with the command SETVAL or SETALL to initialize each
      semaphore.