[mverwijs]

No, in that case, you limit the commands that nagios is allowed to executed using this specific, passphrase-less key.

In this case you would limit this ssh-key to only be able to execute the nagios monitoring scripts. Nothing else.

You do this in ~/.ssh/config on the remote machine.

[rickr]

I believe you mean ~/.ssh/authorized_keys?

For anyone interested here's an SO question with an example: http://stackoverflow.com/questions/402615/how-to-restrict-ss...