source: https://www.securityfocus.com/bid/1071/info

A Denial of service (DoS) attack is possible with the default version of inetd distributed with Data General's DG/UX operating system. By performing a scan utilizing nmap's OS detection option (-O), the inetd daemon is put in a state where it will no longer spawn new services without being restarted.

nmap -O -p 21 <target>
or
nmap -v -O -sS -p1-1023 <target>