For security purposes, administrators may wish to disable telnet (incoming connections) on CentOS / RHEL 6. Follow the steps below to disable telnet permanently on your system.
1. For disabling the telnet server, edit /etc/xinetd.d/telnet and change the field disable to yes.
# vi /etc/xinetd.d/telnet
service telnet
{
flags = REUSE
socket_type = stream
wait = no
user = root
server = /usr/sbin/in.telnetd
log_on_failure += USERID
disable = yes
} 2. Now erestart the xinetd service with the below command.
# service xinetd restart