Unexpected return message from mpirun: "alarm clock"

I have the simplest code "Hello world"开发者_Go百科

#include <stdio.h>  /* printf and BUFSIZ defined there */
#include <stdlib.h> /* exit defined there */
#include <mpi.h>    /* all MPI-2 functions defined there */

int main(argc, argv)
int argc;
char *argv[];
{
   int rank, size, length;
   char name[BUFSIZ];

   MPI_Init(&argc, &argv);
   MPI_Comm_rank(MPI_COMM_WORLD, &rank);
   MPI_Comm_size(MPI_COMM_WORLD, &size);
   MPI_Get_processor_name(name, &length);

   printf("%s: hello world from process %d of %d\n", name, rank, size);

   MPI_Finalize();

   exit(0);
}

I have compiled it

mpicc -o hello hello.c

and tried to run it with 4 processes

mpirun -np 4 hello

it returns;

chasan@ubuntu:~/MpiProgrammes$ mpicc -o hello Hello.c
chasan@ubuntu:~/MpiProgrammes$ mpirun -np 4 hello
Alarm clock
chasan@ubuntu:~/MpiProgrammes$

What could it be ?

try using the command "mpd &"