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
