VirtualBox安装Ubuntu系统，出现“connect: Network is unreachable” 和cannot find device "eth0"问题

总结：还是StackOverflow靠谱，查了一下午资料，最后在Overflow上找到了答案。

I had this problem, there's 4 interfaces on my server, which should have been: eth0, eth1, eth2, eth3 but they were renamed to eth4, eth5, eth6, eth7.

I couldn't figure out how to get them back but eventually found out I could just delete the 70-persistent-net.rules file to make the system reset the interface names back to default

Like so:

rm /etc/udev/rules.d/70-persistent-net.rules

Then a reboot should get everything up and running again:

shutdown -r now

链接：http://stackoverflow.com/questions/10712007/dhcp-on-ubuntu-server-12-04-fails-to-load-eth0

70-persistent-net.rules

Debian/Ubuntu 使用 udev 管理硬體設備，也包括了網路卡。網路卡設備的內容會記錄在 /etc/udev/rules.d/70-persistent-net.rules 。它也會影嚮 NetworkManager 的運作。

當我們使用備份功能將系統複製到新的硬體上之後，會因為新網卡的 MAC address 與 70-persistent-net.rules 內的 MAC address 不相同，導致網路卡未被啟用、網路無法連線。此時，只需要刪除 70-persistent-net.rules ，再重開機，讓系統重新產生 70-persistent-net.rules 即可。

或者，手動編輯 70-persistent-net.rules ，將 ATTR{address}=="..." 的內容刪掉，再重開機。

• Moving an Ubuntu Server install to another machine 
• http://www.debianhelp.co.uk/udev.htm