VSFTPD description of the two files in Ftpusers and user_list and explanations of userlist_enable and Userlist_deny two configuration items in vsftpd.conf

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Question one: What are the respective uses of the ftpusers and user_list two files? What's the relationship?

First, make it clear: Ftpusers is not affected by any of the compounding items , it is always valid and it is a blacklist!
This file is a list of users who are forbidden to access the FTP, usually for security reasons, the administrator does not want to have a large number of accounts (such as root) log in to FTP, in order to avoid uploading or downloading some dangerous location files from the FTP account to damage the system.

And User_list is and vsftpd.conf in the userlist_enable and Userlist_deny two configuration items closely related, it can be effective, also can not be valid, when it can be a blacklist, can also be a white list! So what is the setting that determines its role? This is the question two to explain.

So the simple summary is: Ftpusers and user_list do not have any relationship, Ftpusers file is always effective, user_list depends on userlist_enable and Userlist_deny two configuration.

Question two: vsftpd.conf in the userlist_enable and userlist_deny two configuration items, how do they work with each other?

To illustrate this issue, let's build two test users:

Tom: in the User_list
Jim: Not in User_list

Then we have different values for each of the two configuration items, which are tested in 4 case:

Case 1:userlist_enable=yes, Userlist_deny=yes

Tom: refuse to log in
Jim: Allow Login

Case 2:userlist_enable=yes, Userlist_deny=no

Tom: Allow login
Jim: Deny login (as described in the comments at the beginning of the User_list file, you won't even be prompted for a password, that is, no login prompt, direct deny connection)

Case 3:userlist_enable=no,userlist_deny=no

Tom: Allow login
Jim: Allow Login

Case 4:userlist_enable=no,userlist_deny=yes

Tom: Allow Login
Jim: Allow Login

The following conclusions are drawn from the experiment:

1. The userlist_enable and Userlist_deny two options are combined against the local user (except the user in ftpusers) and the user who appears in the User_list file and not in the User_ The settings for the user collection of these three types of users in the list file.
2. When and only when Userlist_enable=yes: the configuration of the Userlist_deny item is valid, the User_list file is used and, when it is no, regardless of why the value of the Userlist_deny item is invalid, All local Users (except users in ftpusers) can log in to FTP
3. When Userlist_enable=yes, Userlist_deny=yes: User_list is a blacklist , that is, all users appearing on the list will be denied login;
4. When Userlist_enable=yes, Userlist_deny=no: User_list is a whitelist, that is, only users who appear on the list will be allowed to log in (users outside of the user_list are denied login) In addition, a special reminder is that anonymous users will not be able to log in after using the whitelist! Unless you explicitly add a row to the user_list: anonymous
   

Description of the two files in Ftpusers and user_list in vsftpd and explanations of userlist_enable and Userlist_deny two configuration items in vsftpd.conf