1.Telnet命令安装
rpm -qa | grep xinetd
yum -y install xinetd
rpm -qa telnet-server
yum install telnet
service xinetd restart
备注：由于telnet服务是由xinetd守护的，必须先装xinetd,并且安装完telnet-server
要启动telnet服务就必须重新启动xinetd
2.iptables命令安装
当出现Failed to restart iptables.service: Unit not found.错误时
yum install iptables-services
service iptables stop //关闭防火墙