From “man mpirun” - note that not specifying “slots=N” in a hostfile defaults
to slots=#cores on that node (as it states in the text):
Specifying Host Nodes
Host nodes can be identified on the mpirun command line with the -host
option or in a hostfile.
For example,
I am just learning to use openmpi 1.8.4 that is installed on our cluster. I am
running into a baffling issue. If I run:
mpirun -np 3 --host b1,b2,b3 hostname
I get the expected output:
b1
b2
b3
But if I do:
mpirun -np 3 --hostfile hostfile hostname
I get:
b1
b1
b1
Where hostfile contains:
