To allow the spark user to ssh to itself and also the workers, you need ssh passwordless to be enabled. This can be done by logging into the spark user and doing:
ssh-keygen -t rsa -P ""
Once the key has been generated, it will be in /home/spark/.ssh/id_rsa (by default). Copy it to the authorized hosts file (to allow spark to ssh to itself):
cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
Or, for each worker, do something like:
ssh-copy-id -i ~/.ssh/mykey spark@localhost <pre>ssh-copy-id -i ~/.ssh/mykey spark@spark2.lab.bpopp.net