What happens if the password of a user in the /etc/shadow file is prepended with the ! character?

Prepending `!` to a password hash does not grant root privileges; its function is to disable password authentication.

The password is not inverted; instead, the `!` character explicitly marks the password as disabled, preventing any successful password-based login.

This action disables password-based logins specifically; it does not necessarily disable all login methods, as SSH key-based authentication or other methods might still be available.

Disabling a password with `!` prevents login attempts with a password and does not force the user to change their password upon the next login.

When the password field in `/etc/shadow` begins with an `!` character, the system renders the password hash invalid, effectively disabling all password-based login attempts for that specific user. However, other authentication mechanisms, such as SSH key-based authentication, would still work if correctly configured for the user.