First you have to control the FTP Daemon itself. Turning it on through the GUI will only enable it for the single FTP share so make sure it stays turned off in the GUI.
Turn On FTP
sudo -s launchctl load -w /System/Library/LaunchDaemons.ftp.plist
Turn Off FTP
sudo -s launchctl unload -w /System/Library/LaunchDaemons.ftp.plist
Now you have to define a new user for each of your FTP logins in the Server app, give that user a custom home folder so that they automatically log into that folder when the connect via their user name and password, and make that folder a share point if it needs to be accessed from inside the network.
In the Server App...
- Click on Users and create a new local user with the FTP user's login name.
- Right Click on this new user and choose Advanced Options… to set shell to /bin/bash and set Home Directory to the full path of their specific FTP folder
- Click on Server name and click the Access denture choosing the Plus icon to add FTP services adding all your defined FTP users here
- Click on the File Sharing service and add all FTP share points giving access to the FTP user as well as any that need to access the files internally.
Something to note. I've only used this internally and have not tested to see if each ftp home folder is locked down so that a users can't surf out of their folder to get to others. I don't believe the structure will allow it but you should test it if that's important to you.
