[mpich-discuss] send and recieve not working over ethernet

[Pavan Balaji]

Are the architectures of the two machines identical?  Both x86 64-bit?
Did you install a 64-bit OS on both machines ("uname -m" == "x86_64")?

 -- Pavan

On 12/01/2012 08:34 AM US Central Time, D Griffiths wrote:
> I am completely new to MPI so I hope I’m not asking anything too silly.
> I have two computers, one running Ubuntu and the other running
> Scientific Linux. They recognise each other as hosts, I can ssh from
> each without a password and have disabled any firewalls.
> 
> Although I can run a simple Hello World application, the trouble starts
> when I try to use MPI_SEND and MPI_RECV. I am trying a simple program to
> send an int variable from one node to the other (see source code below).
> 
> If I run the code with two processes on the same computer I get the
> correct output:
> 
> dan at siriusa:~/mpich2/tutorial2$ mpiexec -n 2 ./result2
> 
> Process 0 sending number 4
> Process 1 received number 4 from process 0
> 
> However, if I try to run the code using both computers, I get:
> 
> dan at siriusa:~/mpich2/tutorial2$ mpiexec -n 2 -f hosts ./result2
> 
> Process 0 sending number 4
> Process 1 received number -1078477356 from process 0
> 
> My host file:
> 
> dan at siriusa:~/mpich2/tutorial2$ cat hosts
> 
> 192.168.88.1
> 192.168.88.2
> 
> So there is some sort of problemwith using the send/recieve functions
> over the network. As I said I am a beginner at this, so any help will be
> greatly appreciated. Thanks in advance.
> 
> Code:
> 
> #include <mpi.h>
> 
> #include <stdio.h>
> #include <stdlib.h>
> 
> int main(int argc, char** argv) {
> 
>     // Initialize the MPI environment
>     MPI_Init(NULL, NULL);
>     // Find out rank, size
>     int world_rank;
>     MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
>     int world_size;
>     MPI_Comm_size(MPI_COMM_WORLD, &world_size);
>     // Get the name of the processor
>     char processor_name[MPI_MAX_PROCESSOR_NAME];   
>     int name_len;
>     MPI_Get_processor_name(processor_name, &name_len);
> 
>     // We are assuming at least 2 processes for this task
>     if (world_size < 2) {
>         fprintf(stderr, "World size must be greater than 1 for %s\n",
> argv[0]);
>         MPI_Abort(MPI_COMM_WORLD, 1);
>     }
> 
>     int number;
>     if (world_rank == 0) {
>         // If we are rank 0, set the number to -1 and send it to process 1
>         number = 4;
>         printf("Process 0 sending number %d\n",number);
>         MPI_Send(&number, 1, MPI_INT, 1, 0, MPI_COMM_WORLD);
>    
>     } else if (world_rank == 1) {
>         MPI_Recv(&number, 1, MPI_INT, 0, 0, MPI_COMM_WORLD,
> MPI_STATUS_IGNORE);
>         printf("Process 1 received number %d from process 0\n", number);
>     }
>    
>     MPI_Finalize();
> }
> 
> 
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-- 
Pavan Balaji
http://www.mcs.anl.gov/~balaji