int error=system(command);

while (true) {
        MPI_Recv(&so1, 1, MPI_INT, 0, RESPONSE, MPI_COMM_WORLD, &status);
       ...
        while (so1 < so2 && bFinish == false) {
            sprintf(command, "./unrar x -p%d ./file.rar 1>/dev/null 2>/dev/null", so1);
            int err = system(command);

            if (err == 0) { //truong hop dung password
                ....
                break;
            } 
            ...
        }
    }