Whether the ftp daemon is in use or not on a Linux host, it’s a good idea to restrict the system user accounts from using it. Any user ID that is in /etc/passwd that is not permitted to use ftp should be copied to /etc/ftpusers. The following commands for Ubuntu create the file with a list of all users.
sudo awk -F”:” ‘{ print $1 }’ /etc/passwd | sort > ~/ftpusers
Edit the resulting ~/ftpusers to remove the IDs that are allowed to use ftp.
sudo nano ~/ftpusers
Then move the file from your home directory to /etc.
sudo mv ~/ftpusers /etc