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

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. linux networking centos shareimprove this question edited Apr 17 '12 at 19:43 pbm 5,5901728 asked Apr 17 '12 at 18:51 Patryk 693310

1 There is no eth1 on your screenshot... Btw, try to run DHCP on your interface: dhclient eth0 . – pbm Apr 17 '12 at 18:58 @pbm 1) I changed eth1 to eth0 in the description. 2) dhclient eth0 worked :) thanks. How can I make it default - run like this after reboot ? – Patryk Apr 17 '12 at 19:18 I'm not sure, but check out this blog post: blog.malaya-digital.org/… – pbm Apr 17 '12 at 19:49 1 If you find exact solution post it as answer... – pbm Apr 17 '12 at 19:50

2 Answers

activeoldestvotes

up vote 8 down vote accepted

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. shareimprove this answer edited Dec 23 '12 at 2:52 answered Apr 17 '12 at 20:58 Warren Young 17.4k24264

up vote 2 down vote

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.

From:http://unix.stackexchange.com/questions/36705/why-the-default-eth0-interface-is-down-by-default-on-centos