On a new Linux system, the root user is being asked to provide the root user password before being able to use the su command. What line in the /etc/pam.d/su file will allow root to use su without sup

The `pam_norootpw.so` module does not exist, and `required` would still demand other authentication methods if `pam_rootok.so` wasn't present or sufficient.

The `pam_norootpw.so` module does not exist in PAM.

Using `auth required pam_rootok.so` would ensure that `pam_rootok.so` must succeed, but `required` modules still allow subsequent modules in the stack to fail authentication, which might still trigger a password prompt if another module is configured to do so for root.

The `pam_rootok.so` module checks if the current user ID is 0 (root); if it is, the module returns PAM_SUCCESS, and when used with the `sufficient` control flag, it satisfies the authentication requirements without prompting for a password, allowing root to `su` to other users directly.