vsftpd, refer to the following resources.
/usr/share/doc/vsftpd-<version-number>/ directory — Replace <version-number> with the installed version of the vsftpd package. This directory contains a README with basic information about the software. The TUNING file contains basic performance tuning tips and the SECURITY/ directory contains information about the security model employed by vsftpd.
vsftpd related man pages — There are a number of man pages for the daemon and configuration files. The following lists some of the more important man pages.
man vsftpd — Describes available command line options for vsftpd.
man vsftpd.conf — Contains a detailed list of options available within the configuration file for vsftpd.
man 5 hosts_access — Describes the format and options available within the TCP wrappers configuration files: hosts.allow and hosts.deny.