vsftpd users cannot see all files in a directory
 

This is my first time to try and set up vsftpd on RedHat Linux V5.5. I installed vsftpd using the service configuration menu with the default settings.
The users can login, but ls does not list his files.
The response to ls is :
200 PORT command successful. Consider using PASV.
150 Here comes the directory listing.
226 Directory send OK.
A cd to / responds with:
250 Directory successfully changed.
But the response to ls is:
200 PORT command successful. Consider using PASV.
150 Here comes the directory listing.
<some but all of the files are not listed>
226 Directory send OK.
What causes some of the files to be missing?
What is PASV?
Thanks for your help.

pasv is passive mode
(ftp -p <host>)

This is a very good article http://slacksite.com/other/ftp.html

Thanks for the article. That explains the PASV.
But I still cannot see the files in my home directory.
The permissions on the files are rw-rw-rw.
I don't think there is a firewall running, but in passive mode I still cannot see all of the files in the home directory.