Network default configuration for Centos 6/redhat 6 true ~!

http://www.oschina.net/question/17_39276

The old version of the Redhat/centos defaults to install the system, will default to open the network card and set to boot.

But this feature has changed in the latest version 6 ... The NIC will disconnect by default after the reboot.
That is to say, if the server reboots, it will forever break the network ...
And it's hard to understand ...

Because of the 6 version of a guy named Networkmanage.

This is written in the CentOS community Help document:

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The upstream preset has been switched to NetworkManager, and the interface preset is not going to be enabled (it's hard to understand for the Ethernet).

The right thing to do is, in an installation process, wait for the installation program to ask your language, keyboard, basic installation, or other storage device, perform a "check device" and show "please name this computer ..." for the screen. ""

This day has a "Setup Network" button. Clicking on this button will activate the NetworkManager.

Please select the Ethernet link named System eth0 and edit its settings.

If you choose to use the "Auto link" option, the network will be opened after the day.

You can also make this change by NetworkManager ("System, Selection, network", or by clicking on the "edit Links ...") through the network icon in the notification area at the end of the installation, as well.

If you don't use NetworkManager, you can edit the network interface's settings (normal/etc/sysconfig/network-scripts/ifcfg-eth0) and switch onboot=no to Onboot=yes To reach the same demonstration fruit.

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And with the NetworkManager, the usual "ifup eth0" These commands are not used, will prompt you network cable and not connected ...

Pull it off.

Fortunately the solution is very simple, input ntsysv the first networkmanager before the selection of the symbol removed.
Then restart the server to return to management using the "network" and "Ifup/ifdown" operations.