sudo apt-get install openbsd-inetd
sudo apt-get install telnetd

sudo gedit /etc/inetd.conf
/* add below */
telnet stream tcp nowait telnetd /usr/sbin/tcpd /usr/sbin/in.telnetd

sudo /etc/init.d/openbsd-inetd restart

/* for check */
netstat -a | grep telnet
telnet 127.0.0.1