The standard FTP installation places an entry in /etc/inetd.conf, thereby automatically starting the FTP server when an FTP connection is made.
The ftpshut(1m) command creates the file /var/ftp/shutdown which disables FTP.
To reenable FTP, enter the command:
ftpshut enable
This deletes the /var/ftp/shutdown file, allowing subsequent FTP connections to automatically start the FTP daemon.