###
As of proftpd 1.2.0rc3 and later, you need to edit /etc/pam.conf to add
support for ftp.  To do so, add the following three lines to this file:

ftp auth    required    pam_unix.so         try_first_pass
ftp account required    pam_unix.so         try_first_pass
ftp session required    pam_permit.so
###