Why the default eth0 interface is down by default on CentOS?

Question

I am already a little bit familiar with Linux distros like Debian or Ubuntu (yeah, very similar) but I wanted to try Red Hat based - CentOS 6.2 . I have installed it on my Windows 7 host in virtualBox and tried to play with it a little.

I have same across a small problem, namely : the default eth0 interface is down by default. I use the option with NAT ( the virtual machine is 'behind' the host ). Even if I bring the interface up with

ifconfig eth0 up it does not work right away. I get this after bringing the interface up:

What should be done more to configure the network on CentOS machine?

P.S. Sorry for screenshot but I do not know how to get the text out of the VirtualBox.

Answer 1

Edit /etc/sysconfig/network-scripts/ifcfg-eth0. Change the ONBOOT line's value to yes.

In your future installs, pay more attention. You blew past an option in the network configuration section that let you tell it to bring the interface up on boot. This on-boot option is off by default in EL6 now, whereas in previous versions, it was on by default.

As to why this is, I'd guess security reasons. It gives you a chance to tighten things down a bit from the default setup before bringing up the network interface for the first time.

Answer 2

You didn't mention what version of CentOS you are using. If I'm not mistaken, 6.x uses NetworkManager by default.

I rarely install X windows on my servers, so NetworkManager is just a pain for me. I disable it and enable the standard 'network' service.

chkconfig NetworkManager off
chkconfig network on

service NetworkManager stop
service network start

To enable DHCP on the interface, run system-config-network, edit the appropriate device, save, and restart the network service. Alternately, you can edit /etc/sysconfig/network-scripts/ifcfg-eth0 and add

ONBOOT=yes
BOOTPROTO=dhcp

Save changes and restart the network service.