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From: Jeff Squyres \(jsquyres\) (jsquyres_at_[hidden])
Date: 2006-06-29 13:31:38

Sorry for the delay in replying. Too much travel, and too much e-mail!

> -----Original Message-----
> From: users-bounces_at_[hidden]
> [mailto:users-bounces_at_[hidden]] On Behalf Of Michael Kluskens
> Sent: Monday, June 19, 2006 4:56 PM
> To: Open MPI Users
> Subject: Re: [OMPI users] auto detect hosts
> How does OpenMPI auto-detect available hosts?

It doesn't.
> I'm running on a cluster of dual-opterons running Debian Linux.
> Just using "mpirun -np 4 hostname" somehow OpenMPI located the second
> dual-opteron in the stack of machines but no more than that,
> regardless of how many processes I asked for.

I'm surprised that it finds a second host at all if you don't specify a
hostfile (or have some batch scheduler that is specifying other hosts).

If Open MPI doesn't find any host specification at all, it simply uses
the name "localhost". That being said, it is possible to have a default
hostfile in $prefix/etc/openmpi-default-hostfile. If you've added hosts
in there, Open MPI should use them by default (even if you didn't
specify anything on the command line).

Is that the case, perchance?

Jeff Squyres
Server Virtualization Business Unit
Cisco Systems