1. Login to your server as a root user.
2. Edit the file as follows:
# vi /etc/xinetd.d/telnet
3. Look for the line: disable = no and replace with disable = yes
4. Now restart the inetd service:
5. Turn off it through chkconfig as well because it can still start through that.
#/sbin/chkconfig telnet off
6. Scan your server to ensure port 23 is closed.
#nmap -sT -O localhost
Also run ps -aux | grep telnet and if you find anything other than “grep telnet” as result ,then in that case kill that process.