示例命令：
# 重新装载服务
systemctl daemon-reload
在开机时启用一个服务：
systemctl enable xx.service
在开机时禁用一个服务：
systemctl disable xx.service
# 启动xx
systemctl start xx.service
# 查看xx状态
systemctl status xx.service
# 重启xx
systemctl restart xx.service
# 停止xx
systemctl stop xx.service