As a best practice, which of the following should be performed before placing a server on a network?

Securing the disk is a data-protection measure but does not address the network-facing vulnerabilities that emerge when an unhardened OS is first connected.

Securing the server rack is a physical security control and does not protect the OS from network-based threats prior to deployment.

OS hardening involves disabling unnecessary services, removing default accounts, applying patches, and configuring secure settings before the server is exposed to any network traffic. This is a foundational pre-deployment step that prevents attackers from exploiting default or vulnerable configurations the moment the server comes online. Without hardening first, the server is immediately at risk from network-based attacks.

Applications should be installed after the OS is hardened so the underlying platform is already secure before additional software is added.