一旦开始深入研究Linux系统，您可能会发现一些令人困惑或意想不到的事情，例如/usr/bin/false。它为什么在那里？它的目的是什么？今天的超级用户问答帖子回答了一位好奇读者的问题。

今天的问答环节是由SuperUser提供的，SuperUser是Stack Exchange的一个分支，是一个由社区驱动的问答网站分组。

问题

超级用户读者user7326333想知道为什么一些系统用户使用/usr/bin/false作为shell：

Why do some system users have /usr/bin/false as their shell? What does that mean?

为什么有些系统用户使用/usr/bin/false作为shell？

答案

超级用户贡献者杜德，托比·斯佩特，和BBaasssiee为我们提供了答案。首先，伙计：

This helps to prevent users from logging onto a system. Sometimes you need a user account for a specific task. Nevertheless, no one should be able to interact with this account on the computer. These are, on one hand, system user accounts. On the other hand, this is an account for which FTP or POP3 access is possible, but just no direct shell login.

If you look more closely at the /etc/passwd file, you will find the /bin/false command as a login shell for many system accounts. Actually, false is not a shell, but a command that does nothing and then also ends with a status code that signals an error. The result is simple. The user logs in and immediately sees the login prompt again.

接下来是托比·斯佩特的回答：

These users exist to be the owner of specific files or processes and are not intended to be login accounts. If the value of the “shell” field is not listed in /etc/shells, then programs such as FTP daem*** do not allow access. Additionally, for programs that do not check /etc/shells, they make use of the fact that /bin/false will immediately return and deny an interactive shell.

BBaasssiee最后的回答是：

Some users have /usr/bin/false, others have /**in/nologin, or they may even have /usr/bin/passwd. They can either be system users that are needed to isolate program permissi*** or human users of programs that use the password files for authentication.

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