mjhjmtu

am setting-up a Beowulf cluster with Ubuntu 16.04 LTS as the OS. I was able to follow the steps described in https://www.youtube.com/watch?v=gvR1eQyxS9I very closely until the code compilation stage wherein I get the following error :

*cdil@master:/nfs$ mpirun --hostfile machinefile -np 28 ./mpi_hello

Host key verification failed.

ORTE was unable to reliably start one or more daemons.
This usually is caused by:

• not finding the required libraries and/or binaries on
  one or more nodes. Please check your PATH and LD_LIBRARY_PATH
  settings, or configure OMPI with --enable-orterun-prefix-by-default




• lack of authority to execute on one or more specified nodes.
  Please verify your allocation and authorities.




• the inability to write startup files into /tmp (--tmpdir/orte_tmpdir_base).
  Please check with your sys admin to determine the correct location to use.




• compilation of the orted with dynamic libraries when static are required
  (e.g., on Cray). Please check your configure cmd line and consider using
  one of the contrib/platform definitions for your system type.



• 
  

  an inability to create a connection back to mpirun due to a
  lack of common network interfaces and/or no route found between
  them. Please check network connectivity (including firewalls

  
  
  

  and network routing requirements).

  
  

cdil@master:/nfs$*
The cluster consists of a total of 7 nodes with 4 cpus per node, with the server called master and slave nodes named node1,node2,node3.... I looked deeper into the error message and reset all the keys in my ~/.ssh/knownhosts file. I did a ssh-copy-id noden ( n=1,2,3..) on master. Upon doing so, I was able to login to any node using ssh cdil@node. This didn't really solve the host key verification problem.

I tried logging into the master from one of the nodes and discovered that it fails to do so. I get a password prompt for master after which it simply fails to connect without any error message.

cdil@node1:~$ ssh cdil@master
cdil@master's password:
Welcome to Ubuntu 16.04.3 LTS (GNU/Linux 4.10.0-37-generic x86_64)

0 packages can be updated.
0 updates are security updates.

Last login: Wed Oct 18 11:18:45 2017 from 10.194.63.97
cdil@node1:~$
I am able to ping back and forth from master and node successfully.

I will be grateful if anyone can suggest a solution to this problem.

Thank you