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From: Michael Kluskens (mkluskens_at_[hidden])
Date: 2006-07-14 10:07:45


On Jun 29, 2006, at 1:31 PM, Jeff Squyres (jsquyres) wrote:

>> 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).

I discovered much later that apparently I had modified the default
hostfile a long time ago. This needs to be documented in a couple
more places, obviously I read about it once or twice and then never
saw that buried documentation again in related documentation.

Michael