之前装好的虚拟机突然不能上网了，具体报错如下：
systemctl network restart
Restarting network (via systemctl): Job for network.service failed because the control process exited with error code. See "systemctl status network.service" and "journalctl -xe" for details.
[失败]
使用systemctl status network.service命令查看结果如下：
network.service - LSB: Bring up/down networking
Loaded: loaded (/etc/rc.d/init.d/network)
Active: failed (Result: exit-code) since 三 2016-08-17 11:34:36 CST; 54s ago
Docs: man:systemd-sysv-generator(8)
Process: 3847 ExecStart=/etc/rc.d/init.d/network start (code=exited, status=1/FAILURE)
8月 17 11:34:36 python.cn network[3847]: RTNETLINK answers: File exists
8月 17 11:34:36 python.cn network[3847]: RTNETLINK answers: File exists
8月 17 11:34:36 python.cn network[3847]: RTNETLINK answers: File exists
8月 17 11:34:36 python.cn network[3847]: RTNETLINK answers: File exists
8月 17 11:34:36 python.cn network[3847]: RTNETLINK answers: File exists
8月 17 11:34:36 python.cn network[3847]: RTNETLINK answers: File exists
8月 17 11:34:36 python.cn systemd[1]: network.service: control process exited, code=exited status=1
8月 17 11:34:36 python.cn systemd[1]: Failed to start LSB: Bring up/down networking.
8月 17 11:34:36 python.cn systemd[1]: Unit network.service entered failed state.
8月 17 11:34:36 python.cn systemd[1]: network.service failed.
查看系统日志more /var/log/messages |grep network，报错如下：
Aug 17 11:34:36 python network: RTNETLINK answers: File exists
Aug 17 11:34:36 python network: RTNETLINK answers: File exists
Aug 17 11:34:36 python network: RTNETLINK answers: File exists
Aug 17 11:34:36 python network: RTNETLINK answers: File exists
Aug 17 11:34:36 python network: RTNETLINK answers: File exists
Aug 17 11:34:36 python network: RTNETLINK answers: File exists
Aug 17 11:34:36 python network: RTNETLINK answers: File exists
Aug 17 11:34:36 python network: RTNETLINK answers: File exists
Aug 17 11:34:36 python network: RTNETLINK answers: File exists
Aug 17 11:34:36 python systemd: network.service: control process exited, code=exited status=1
Aug 17 11:34:36 python systemd: Failed to start LSB: Bring up/down networking.
Aug 17 11:34:36 python systemd: Unit network.service entered failed state.
Aug 17 11:34:36 python systemd: network.service failed.
Aug 17 11:36:28 python systemd: Starting LSB: Bring up/down networking...
Aug 17 11:36:29 python network: 正在打开环回接口： 无法载入文件 '/etc/sysconfig/network-scripts/ifcfg-lo'
Aug 17 11:36:29 python network: 无法载入文件 '/etc/sysconfig/network-scripts/ifcfg-lo'
Aug 17 11:36:29 python network: 无法载入文件 '/etc/sysconfig/network-scripts/ifcfg-lo'
Aug 17 11:36:29 python network: 无法载入文件 '/etc/sysconfig/network-scripts/ifcfg-lo'
Aug 17 11:36:29 python network: [ 确定 ]
Aug 17 11:36:29 python network: 正在打开接口 eno16777736： 错误：激活连接失败：No suitable device found for this connection.
经查，确认/etc/sysconfig/network-scripts/ifcfg-lo文件是存在的。
百度答案：
mac地址不对，修改mac地址。
编辑文件，加入mac地址。
vi /etc/sysconfig/network-scripts/ifcfg-eno16777736
HWADDR=
Google答案，跟系统自带的NetworkManager这个管理套件有关系，关掉就可以解决。
systemctl stop NetworkManager
systemctl disable NetworkManager
重新启动网络：
systemctl start network.service
或重启reboot，再次查看网络systemctl status network。
网络正常启动，访问正常。
