I would like to know what makes a virtual user in vsftpd (although I suppose it's the same with other ftp daemons too) use "ftp"? I don't understand where the association is being done?

For instance, it's easy to understand that apache uses the "apache" user in Centos, especially given that there's a special directive within httpd.conf. What about ftp then? How does this work exactly?

Hi,

I think I need to clarify a thing on Apache.
While the httpd process is in initial phases, just after the "administrative" tasks (such binding to the 80 TCP port), the root privileges are droppedto user and group apache.
Differently, for vsftpd the process is run under root privileges.

That said, when a client initiate a FTP session on a vsftpd server, the client must specify the user it wants to use in order to pass the authentication (username + password) phase.

I understand, but when you specify a virtual user, things are quite different. It's not a system user, it's actually the "ftp" user's permissions being used. So how come is "ftp" and not another used? This is the case in Centos, at least.

Hi,

ftp user is a system (uid < 1000 in CentOS 7) username.
You can convince yourself by doing id ftp or grep ftp /etc/passwd.

I do not know what you really mean by virtual user, but maybe the two options of vsftpd.conf: ftp_username and guest_username can achieve what you want.
Obviously I strongly recommend you to read man 5 vsftpd.conf.

When I say virtual user, I mean not using the actual system users. By virtual user, I mean, for instance, users taken from a database (for instance, one created with dbload). What I mean by virtual users is what the creator of vsftp means by it. The notion shows up in the vspft.conf manual, also.

It's obvious that the users, eventually, need to use a real system user to actually make actual changes. And that's the "ftp" user. And that's exactly what I'm asking. Why is it ftp, and why not another real user? Where is the association being made?

In man pages it says: ftp_username
This is the name of the user we use for handling anonymous FTP.

Now, I know this is obviously related to allow_anonymous, but I suppose it means, basically, that you are allowed as any user you may choose. Which is quite different from using virtual users. I'm also guessing that it's not related to the hide_ids directive.

So yes, simply reading the manual pages (which I read, partially, when looking for various directives) isn't of much help by itself.

Hi,

Now, I have a better understanding of your needs.
Unfortunately, I have never played with vsftpd using users that are not system users.