Which configuration option can you use to prevent the root user from logging directly onto a machine using ssh?

`NoRootLogon` is not a standard or recognized directive in the `sshd_config` file for preventing root login.

The `PermitRootLogin No` directive in the SSH server's configuration file (`/etc/ssh/sshd_config`) prevents the root user from logging in directly via SSH for security reasons, often requiring users to log in as a regular user and then use `su` or `sudo`.

`NoRootLogon Yes` is not a standard `sshd_config` directive.

`RootLogin = No` is not the correct syntax or directive for preventing root login in `sshd_config`; the correct directive is `PermitRootLogin`.

`ProhibitRootLogon No` is not a standard or recognized directive in the `sshd_config` file.