Scenario: FTP user is jailed to their home directory with chroot. FTP user needs to access an external directory (such as www).
Normally you would create a symbolic link in the user’s home directory.
ln -s /var/www/html/userdomain.com www
But for some reason, this just doesn’t work with VSFTPD. After fiddling with permissions unsuccessfully for a few minutes, I found a better way.
mount --bind /var/www/html/userdomain.com www
So you could either do it this way, or use PROFTPD.