he system call returns the value of semval for the semnum-th semaphore of the set. The calling process must have read access privi­ leges on the semaphore set. GETZCNT The system call returns the value of semzcnt for the semnum-th semaphore of the set (i.e. the number of processes waiting for semval of the semnum-th semaphore of the set to become 0). The calling process must have read access privileges on the semaphore set. SETALL Set semval for all semaphores of the set using arg.array, updating also the sem_ctime member of the semid_ds structure associated to the set. Undo entries are cleared for altered semaphores in all processes. Processes sleep­ ing on the wait queue are awakened if some semval becomes 0 or increases. The argument semnum is ignored. The calling process must have alter access privileges on the semaphore set. SETVAL Set the value of semval to arg.val for the semnum-th semaphore of the set, updating also the sem_ctime member of the semid_ds structure cesses sleeping on the wait queue are awakened if semval becomes 0 or increases. The calling process must have alter access privileges on the semaphore set.

RETURN VALUE

       On  fail  the system call returns -1 with errno indicating
       the error.  Otherwise the system call returns  a  nonnega­
       tive value depending on cmd as follows:

       GETNCNT    the value of semncnt.

       GETPID     the value of sempid.

       GETVAL     the value of semval.

       GETZCNT    the value of semzcnt.

ERRORS

       For  a  failing return, errno will be set to one among the
       following values:

       EACCES     The calling process has no  access  permissions
                  needed to execute cmd.

       EFAULT     The  address pointed to by arg.buf or arg.array
                  isn't accessible.

       EIDRM      The semaphore set was removed.

       EINVAL     Invalid value for cmd or semid.

       EPERM      The argument cmd has value IPC_SET or  IPC_RMID
                  but  the  calling process effective user-ID has
                  insufficient privileges to execute the command.

       ERANGE     The argument cmd has value SETALL or SETVAL and
                  the value to which semval has to  be  set  (for
                  some  semaphore  of  the set) is less than 0 or
                  greater than the implementation value SEMVMX.

NOTES

       The IPC_INFO, SEM_STAT and SEM_INFO control calls are used
       by the ipcs(8) program to provide information on allocated
       resources.  In the future these can be modified as  needed
       or moved to a proc file system interface.

       The  following  system  limit  on semaphore sets affects a
       semctl call:

       SEMVMX     Maximum value for semval: implementation depen­
                  dent (32767).

       SVr4,  SVID.   SVr4 documents more error conditions EINVAL
       and EOVERFLOW.

SEE ALSO

       ipc(5), shmget(2), shmat(2), shmdt(2)
/B> The argument s is not a socket. EFAULT An invalid user space address was specified for a parameter. EMSGSIZE The socket requires that message be sent atomi­ cally, and the size of the message to be sent made this impossible. EAGAIN The socket is marked non-blocking and the requested operation would block. ENOBUFS The system was unable to allocate an internal mem­ ory block. The operation may succeed when buffers become available. EINTR A signal occurred. ENOMEM No memory available. EINVAL Invalid argument passed. also receive a SIGPIPE unless MSG_NOSIGNAL is set.

CONFORMING TO

       4.4BSD, SVr4, POSIX 1003.1g draft  (these  function  calls
       appeared in 4.2BSD).

SEE ALSO

       fcntl(2),  recv(2),  select(2),  getsockopt(2), socket(2),
       write(2), socket(4), ip(4), tcp(4), udp(4)
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