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Subject: Re: [OMPI users] Setting up Open MPI to run on multiple servers
From: Rayne (lancer6238_at_[hidden])
Date: 2008-08-12 22:52:15

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, although 'which' gave me the correct location. Then I modified the /etc/ 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.


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