We live in a world where data is an incredibly valuable currency, and you are always at risk of loss. Because of this, you must do everything you can to ensure what you hold on your desktops and servers is safe. If you are looking to lock down your Linux servers and desktops as tight as possible, you should consider to make use of two-factor authentication. This article explains how to configure two factor authentication using pam_u2f.
Sometimes it can be useful to get notified when someone logs into the system via SSH. This article shows several possible solutions how to configure those notifications.