拷貝了個虛擬機，有兩個網卡，1個可以起來，另一個起不來。運行命令：
$>systemctl restart network
輸出如下：Job for network.service failed because the control process exited with error code. See "systemctl status network.service" and "journalctl -xe" for details.
根據提示，繼續運行
$>systemctl status network.service ，輸出：
● network.service - LSB: Bring up/down networking
Loaded: loaded (/etc/rc.d/init.d/network; bad; vendor preset: disabled)
Active: failed (Result: exit-code) since Fri 2017-05-05 17:34:58 CST; 4min 48s ago
Docs: man:systemd-sysv-generator(8)
Process: 5470 ExecStop=/etc/rc.d/init.d/network stop (code=exited, status=0/SUCCESS)
Process: 5668 ExecStart=/etc/rc.d/init.d/network start (code=exited, status=1/FAILURE)
May 05 17:34:57 head systemd[1]: Starting LSB: Bring up/down networking...
May 05 17:34:58 head network[5668]: Bringing up loopback interface: [ OK ]
May 05 17:34:58 head network[5668]: Bringing up interface enp0s3: Connection successfully activated (D-Bus a...ion/4)
May 05 17:34:58 head network[5668]: [ OK ]
May 05 17:34:58 head network[5668]: Bringing up interface enp0s8: Error: Connection activation failed: No su...ction.
May 05 17:34:58 head network[5668]: [FAILED]
May 05 17:34:58 head systemd[1]: network.service: control process exited, code=exited status=1
May 05 17:34:58 head systemd[1]: Failed to start LSB: Bring up/down networking.
May 05 17:34:58 head systemd[1]: Unit network.service entered failed state.
May 05 17:34:58 head systemd[1]: network.service failed.
Hint: Some lines were ellipsized, use -l to show in full.
ifup也起不來
$> ifup enp0s8
Error: Connection activation failed: No suitable device found for this connection.
網上搜了一通，然並卵，發現虛擬機右上角只能顯示一個網卡，另一個顯示不出來
分明就是沒連上這個網卡了，到vbox里查看發現
接入網線選項沒勾上！
選上之后重啟網卡，一切ok(無須重啟機器)。