semctl
semctl - SysV semaphore control operations
semctl ID,SEMNUM,CMD,ARG
Calls the System V IPC function semctl. If CMD is &IPC_STAT or
&GETALL, then ARG must be a variable which will hold the returned
semid_ds structure or semaphore value array. Returns like ioctl: the
undefined value for error, ``0 but true'' for zero, or the actual return
value otherwise.