So that Nagios can run plugins over the secure shell remotely and automatically, it—or, strictly speaking, the user
nagios on the Nagios server—must not be distracted by any password queries. This is avoided with a login via a Public Key mechanism.
The key pair required to do this is stored by the key generator
ssh-keygen by default in the subdirectory
.ssh of the respective user's home directory (for the user
nagios, this therefore corresponds to the installation guide in 1.2 Compiling Source Code from page 39, that is,
/usr/local/nagios). If it is also sent on its way with the
option (without path specification), it will land in the current working directory, ...