Monitoring Fujitsu ETERNUS storage with supplied plugin in Ubuntu 18.04



I am trying to use the Fujitsu ETERNUS Nagios plugin in Ubuntu 18.04 but cannot seem to be able to connect using the plugin. The nagios user can log into the ETERNUS console just fine, when using the plugin an error is generated (ssh return code = 255).

It seems to be the same problem as described here:

The OP did not supply detailed information about how it was solved though.

Any ideas?