云服务器开启很多不必要的端口，造成安全隐患
TCP
25端口：邮件服务
systemctl stop postfix
53端口 ：域名解析服务
systemctl stop rhel-domainname
111端口：SUN公司的RPC服务所有端口
systemctl stop rpcbind
systemctl stop rpcbind.socket
systemctl stop rpcbind.target
631端口：打印服务
systemctl stop cups
UDP
5353端口：多播DNS(multicastDNS)/DNS-SD网络服务
systemctl stop avahi-daemon
systemctl stop avahi-daemon.socket
查看端口命令:
grep 端口号 /etc/services|head
一键停止禁用:
ss -ntlp systemctl stop rhel-domainname systemctl stop cups systemctl stop rpcbind systemctl stop rpcbind.socket systemctl stop rpcbind.target systemctl stop dnsmasq systemctl stop postfix systemctl stop avahi-daemon
systemctl stop avahi-daemon.socket
ifconfig virbr0 down
brctl delbr virbr0 systemctl disable rpcbind systemctl disable rpcbind.socket systemctl disable rpcbind.target systemctl disable cups systemctl disable dnsmasq systemctl disable rhel-domainname systemctl disable postfix
systemctl disable avahi-daemon
systemctl disable avahi-daemon.socket
systemctl disable libvirtd
ss -ntlp
exit