centos 7
关闭防火墙：
systemctl stop firewalld.service #停止firewall
systemctl disable firewalld.service #禁止firewall开机启动
启动一个服务：systemctl start firewalld.service
关闭一个服务：systemctl stop firewalld.service
重启一个服务：systemctl restart firewalld.service
显示一个服务的状态：systemctl status firewalld.service
在开机时启用一个服务：systemctl enable firewalld.service
在开机时禁用一个服务：systemctl disable firewalld.service
查看服务是否开机启动：systemctl is-enabled firewalld.service;echo $?
查看已启动的服务列表：systemctl list-unit-files|grep enabled
http://www.ruanyifeng.com/blog/2016/03/systemd-tutorial-commands.html
