Duo Security 为 Unix 系统提供双因素身份验证：duo_unix。对于少于 10 个用户的开源项目和安装来说，它是免费的。
免责声明，我是 Duo 开发人员。
Duo Security provides two-factor authentication for Unix systems: duo_unix. It is free for open source projects and installations with less than ten users.
Would you consider something like OPIE? (an S/KEY based OTP system). You should be able to set PAM up to require both a password and the OTP value, and most smartphones can run a generator.
Duo Security 为 Unix 系统提供双因素身份验证：duo_unix。对于少于 10 个用户的开源项目和安装来说，它是免费的。
免责声明，我是 Duo 开发人员。
Duo Security provides two-factor authentication for Unix systems: duo_unix. It is free for open source projects and installations with less than ten users.
Disclaimer, I am a Duo developer.