After installing MPI on a node, the next step is to set up password-less SSH access for the master node. This requires the SSH server to be installed on the node (part of the ssh package on Debian-based distributions). After this we need to generate and install the SSH key.

One way to easily do this is by having a common user on the master node and other nodes, and using an NFS network share or similar to mount the user folder on the master node on the compute nodes. This way all nodes would have the same SSH key and known hosts file. One disadvantage of this approach is the lack of security. For an internet-connected cluster, this would not be a very good approach.

It is, however, a definitely good idea to run the job on each node as the same user to prevent any possible permission issues, especially when using files and other resources. With the common user account created on each node, and with the SSH key generated, we can transfer the public key to the node using the following command:

    $ ssh-copy-id mpiuser@node1

Alternatively, we can copy the public key into the authorized_keys file on the node system while we are setting it up. If creating and configuring a large number of nodes, it would make sense to use an image to copy onto each node's system drive, use a setup script, or possibly boot from an image through PXE boot.

With this step completed, the master node can now log into each compute node in order to run jobs.