虚拟机安装完图形界面后，在某次重启后突然不能用ssh连接了，一看网卡没启动
我的是Cent os 7.3
当执行 ifup ens33启动网卡出现如下报错：

[he@python_centos ~]$ ifup ens33
Error: failed to load connection: access denied.
Users cannot control this device.

解决办法如下：

[he@python_centos ~]$ chkconfig NetworkManager off
Note: Forwarding request to 'systemctl disable NetworkManager.service'.
Removed symlink /etc/systemd/system/multi-user.target.wants/NetworkManager.service.
Removed symlink /etc/systemd/system/dbus-org.freedesktop.NetworkManager.service.
Removed symlink /etc/systemd/system/dbus-org.freedesktop.nm-dispatcher.service.
Removed symlink /etc/systemd/system/network-online.target.wants/NetworkManager-wait-online.service.

[he@python_centos ~]$ chkconfig network on
You do not have enough privileges to perform this operation.

[he@python_centos ~]$ sudo chkconfig network on

[he@python_centos ~]$ service NetworkManager stop
Redirecting to /bin/systemctl stop  NetworkManager.service

[he@python_centos ~]$ service network start
Starting network (via systemctl):                          [  OK  ]

OK！大功告成，查看ip地址已经能正常显示