[derekm]

IF you have a small cluster of more than 3 nodes using SSH and are upgrading from openfoam 2.3.1 or earlier to 2.4 and later you may run into this OpenMPI problem if you have upgraded OpenMPI to later than 1.6.5

with the upgrade to openmpi then you may find the following error occurring in a previously perfectly working cluster.

"Host key verification failed."

This stalled me for a couple of days trying to diagnose/ research/ fix it.

After version 1.6.5 Openmpi has changed the way it launches. It now launches in a binary tree fashion, you will get the above error message if you use more than 3 nodes and only have passwordless ssh from the head node to the slaves. The error occurs when one of the slaves attempts to launch another slave.There are ways to solve this

• A job manager using centralised authentication
• Make ssh omnidirectional
• Use the flag to disable "tree spawning"as shown in http://www.open-mpi.org/community/li...4/04/24157.php