Setting a strong, unique password for service accounts is essential as it ensures that each service has its distinct access credentials, which can prevent unauthorized access if one service is compromised. Locking service accounts with shell access adds an additional layer of security. Disabling login capabilities entirely for service accounts is the most secure practice because it mitigates the risk of these accounts being used to gain unauthorized system access. While changing the default shell to /bin/false or nologin reduces the functionality of the account for interactive use, it does not prevent the account from executing its service-related tasks. The reason this is the best practice is that it does not rely on password strength or the potential for a password to be compromised, as it altogether disables the ability for the service account to be used for direct logins. Service accounts should not be used for interactive logins, and their purpose is to run the corresponding service. Changing the home directory permissions and using PAM modules are also good security practices, but they do not restrict login capabilities as effectively as setting the shell to nologin.