1. run

# yum install telnet telnet-server -y

2. modify config

# vim /etc/xinetd.d/telnet

Set disable = no

# default: on
# description: The telnet server serves telnet sessions; it uses \
#       unencrypted username/password pairs for authentication.
service telnet
{
        flags           = REUSE
        socket_type     = stream
        wait            = no
        user            = root
        server          = /usr/sbin/in.telnetd
        log_on_failure  += USERID
        disable         = no
}

3. start and auto run service

# service xinetd start
# chkconfig telnet on
# chkconfig xinetd on