The Configuration File
The first step in configuring a proftpd daemon is knowing where the configuration file, usually named proftpd.conf, is located. The default location for this file is /etc/proftpd.conf or /usr/local/etc/proftpd.conf, depending on your installation. When starting the daemon, the exact path to the configuration file to be used can always be specified using the -c command-line option.

The idea behind proftpd's handling of the configuration file is that a blank file can be used, and the daemon will still operate. This means that, unlike Apache, there is a "default" server configuration in every proftpd.conf; ProFTPD does not require that all server configurations be explicitly written in the proftpd.conf file. This default server attempts to bind to the IP address of the hostname indicated by the hostname(1) command.

Configuration Format
The format of the proftpd.conf file is deliberately designed to resemble the format used by Apache: lines of configuration directives contained with different contexts. A list of the configuration directives for ProFTPD is available here:

  http://www.proftpd.org/docs/

  http://www.castaglia.org/proftpd/doc/contrib/configuration-directive-key.html

Two new configuration directives were introduced in 1.2.6rc1: <IfModule> and <IfDefine>. These work exactly like Apache's directives of the same names, providing the ability to have conditional sections in the configuration file.

Starting the Daemon
One of the first decisions you will need to make is whether you will be running your ProFTPD server as an inetd service, or as a standalone server. This is controlled in the proftpd.conf using the ServerType configuration directive:

  http://www.castaglia.org/proftpd/doc/contrib/ProFTPD-mini-HOWTO-ServerType.html

Server Identity
The daemon must be started with root privileges in order to do things like binding to port 21 and chrooting FTP sessions. However, it is not a good idea to leave a long-lived process running as root. The User and Group configuration directives are thus recommended. These directives configure the identity to which the daemon will switch, after accomplishing its startup tasks. The daemon will switch to the configured User and Group in the "server config" context. (Note that this switch uses the effective UID/GID, not the real UID/GID. Some programs, such as top, will continue to report proftpd as running as root; this is because the program displays the real UID/GID of processes. The proftpd daemon retains root privileges for operations such as chroots and binding to port 20 for active data transfers. If you wish proftpd to drop all root privileges, use the RootRevoke configuration directive.)

For this reason, it is recommended that a non-privileged identity be used. Many sites choose to use user nobody. Historically, this role account was used by NFS-related processes; over time, many other applications default to using user nobody. This has the side-effect of adding to the "privileges" held by user nobody, in terms of files owned and/or accessible by that user. Instead, I personally recommend that a new role account be created for use specifically by the daemon, a user ftpd, and perhaps even a group ftpd. Many systems that run Apache have a user www or user apache for use by the httpd daemon; similarly, a separate user should be created for the proftpd daemon.

In the default configuration file that accompanies the proftpd source code, there appears:

  User nobody
  Group nogroup

Logging in
By default, the proftpd daemon reads the host's /etc/passwd file for logging in users. This means that to add FTP users, you simply need to create new system accounts for those users in your /etc/passwd file.

Sometimes, though, sites want "virtual", FTP-only users. In order to support such configurations, the AuthUserFile configuration directive can be used:

  http://www.castaglia.org/proftpd/doc/contrib/ProFTPD-mini-HOWTO-AuthFiles.html

For setting up anonymous logins, there is the <Anonymous> configuration context. If there are no <Anonymous> sections in your proftpd.conf, then no anonymous logins will be allowed - simple. As mentioned in the description, the User directive in an <Anonymous> context determines what username is treated as an anonymous login. The main other thing to know about anonymous logins is that ProFTPD automatically chroots anonymous logins.

For normal, non-anonymous logins, jails/chroots are configured using the DefaultRoot directive. This is the configuration directive used to restrict users to their home directories, to keep them from browsing around the site. There is a mini-HOWTO covering chrooting:

  http://www.castaglia.org/proftpd/doc/contrib/ProFTPD-mini-HOWTO-Chroot.html

If you use <VirtualHost> sections, and it seems that your server configuration is not being seen by connecting clients, you might need to check that, if using a DNS name instead of an IP address in your <VirtualHost> line, that name resolves to an IP address different from that of the "default" server. Many people new to ProFTPD get the impression that since the configuration syntax looks similar to Apache's, things like name-based virtual hosting will work as well. Unfortunately, this is not possible. It is not a limitation in ProFTPD, but rather in the RFCs that define FTP. See the virtual server mini-HOWTO for more information.

As a workaround, some sites configure virtual servers to run on non-standard ports, using the Port configuration directive. As long as the clients are aware of the non-standard port, this scheme works well. One minor little caveat to keep in mind, when using this approach, is the numbers used: the RFCs mandate that the daemon, for the purposes of active data transfers (as opposed to passive) use port L-1 as the source port for the data connection, where L is the port number at which the client contacted the server. This means that servers that use the standard port 21 for FTP will use port 20 as the source port for their active data transfers. Passive data transfers do not have this restriction. The restriction comes into play when choosing non-standard port numbers for virtual hosts. For example, this configuration would cause problems for clients of the second virtual server that wanted to use active data transfers:

  <VirtualHost a.b.c.d>
    Port 2121
    ...
  </VirtualHost>

  <VirtualHost a.b.c.d>
    Port 2122
    ...
  </VirtualHost>

Access Restrictions
Many sites like to have specific directories for uploads, and other directories only for downloads; some sites like to allow downloads, but no browsing of directories or their contents. For configurations to achieve this, use combinations of the <Directory> and <Limit> configuration directives. There are separate mini-HOWTOs that cover these directives:

  http://www.castaglia.org/proftpd/doc/contrib/ProFTPD-mini-HOWTO-Directory.html
  http://www.castaglia.org/proftpd/doc/contrib/ProFTPD-mini-HOWTO-Limit.html

Further Questions
Hopefully this document answers some of your questions, or at least enough to get you started. In addition, you should take a look at some of the example configuration files. Once you are comfortable with the configuration file format, a reading of all the configuration directives' descriptions is recommended, especially if you plan on having more complex configurations. When trying to figure out why something is not working, make use of server debugging output:

  http://www.castaglia.org/proftpd/doc/contrib/ProFTPD-mini-HOWTO-Debugging.html