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, 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.''

     The key IPC_PRIVATE will create an identifier and associated
     data structure that is unique to the calling process and its
     children.

     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.

STATUS MESSAGES AND VALUES
     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.

     The semget command will fail if one or more of the following
     is true:



January 1992                                                    1

semget(2)                                               semget(2)



     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.

     EEXIST
          A semaphore identifier exists for key but ((semflg &
          IPC_CREAT) && (semflg & IPC_EXCL)) is ``true.''

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


























2                                                    January 1992