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Subject: Re: [OMPI users] Setting up Open MPI to run on multiple servers
From: jody (jody.xha_at_[hidden])
Date: 2008-08-13 02:56:26


Hi Rayne

SSH is used to start processes on the other machines - that's why you
must configure ssh to work without passwords.

As to your 64/32 bit problem: a program compiled for 32 bits usually
works on a 64 bit machine,
but not vice versa. There are methods to start MPI such that different
executables are started
on different machines, but iguess the easiest way to get things going
would be to use
32 bit versions of your program on all your machines.

Jody

On Wed, Aug 13, 2008 at 4:52 AM, Rayne <lancer6238_at_[hidden]> wrote:
> Thank you for all the replies.
>
> Here's what I have now.
>
> I modified my .bash_profile on my server to include the path of my executables, and now mpiexec and mpicc both point to the correct ones. I tried setting the LD_LIBRARY_PATH too, but it didn't seem to work, as it kept telling me it couldn't find the sharded library libmpi.so.0, although 'which libmpi.so.0' gave me the correct location. Then I modified the /etc/ld.so.conf file to include the directory of the libraries, and now the MPI programs work correctly on the server.
>
> Now, my problem is that I have trouble running the program using my PC and remotely on my server. I have the IP address of my server in the openmpi-default-hostfile in my PC, and I have set up a password-less ssh between them (though I have set it up such that it asks for a passphrase). All my programs and executables are in the shared folder. However, when I tried to run the program on my PC using 'mpiexec -n 2 ./a.out', I get the following error:
>
> "Failed to find or execute the following executable:
>
> Host: (Name of my server)
> Executable: ./a.out
>
> Cannot continue."
>
> If I try to compile then execute the program locally, on both my PC and server, they run fine. It's only when I try to get both PC and server to run the program concurrently, (which is the purpose of using MPI) that I get the error. I have checked and the a.out file is exactly the same on the PC and server, in terms of the size and date/time modified.
>
> One thing is that my PC is a 64-bit machine, and my server is a 32-bit machine. Could this be a factor, that a program compiled on a 64-bit machine cannot run on a 32-bit machine?
>
> Also, I don't quite understand the mechanism of how MPI allows one machine to communicate with another. For example, after compiling a program, an executable is created and stored on that machine and also on the remote nodes, through the use of a shared system. So when I run the program, how does the machine I'm at get the remode nodes to run the program too?
>
> Thank you, and sorry for the long email.
>
> Regards,
> Rayne
>
>
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