A Linux administrator attempts to log in to a server over SSH as root and...

The SSH configuration option PermitRootLogin prohibit-password prevents the root user from logging in with password authentication. This setting means root cannot use a password to log in via SSH; only key-based authentication is permitted for root. The administrator can still log in as root locally, which is not affected by this SSH configuration. To allow SSH access as root, the administrator must use an SSH key instead of a password.

Other options:

A. MaxSessions controls the number of simultaneous SSH sessions but is not causing the login denial here.

B. PAM (Pluggable Authentication Modules) is disabled, but enabling it is not required for basic SSH authentication.

C. Changing the SSH port is unrelated to the authentication method issue.