The /etc/ftpaccess file - Administration: "In ftpaccess, you're creating a plan for who can do what. With non-anonymous chroot access, you want to create a set of guestgroups, each of which corresponds directly to entries in the /etc/group file. You should repeat these entries in the chroot'd group file, too, with the same IDs.
Here are the lines you need to make sure are in the ftpaccess file to make this all work. Let's assume three groups: frogstar, bilbo, and foobar. I'm only including the parts that are specifically necessary to make non-anonymous access work; you can leave the rest of the model file the same, or read the man page to figure out how to further customize."
'via Blog this'