centos 7 中的类似 "service httpd start " 服务启动，停止，重启指令， “service” 已更改为 “systemctl” 。具体示例如下：
systemctl start httpd.service /启动Apache httpd
systemctl restart httpd.service /重新启动
systemctl stop httpd.service /停止服务
同样类似 "chkconfig httpd on" 设置服务开机启动项，指令已更改为 “systemctl enable” ，具体示例如下：
systemctl enable httpd.service /开机启动httpd
systemctl disable httpd.service /禁止开机启动httpd
