eth0


CentOS: prevent eth0 from starting at boot time

On a CentOS server we own, we had to disable eth0 from starting at boot time
To do so we needed to modify the file /etc/sysconfig/network-scripts/ifcfg-eth0 and set the value ONBOOT="yes" to ONBOOT="no".

Using you favorite text editor, make this change and restart your machine to verify that the change was successful.

Below is the sample content of /etc/sysconfig/network-scripts/ifcfg-eth0 after the change was applied to prevent eth0 from starting at boot time.

  GNU nano 2.3.1                File: /etc/sysconfig/network-scripts/ifcfg-eth0                             Modified

TYPE="Ethernet"
 BOOTPROTO=dhcp
 DEFROUTE="yes"
 IPV4_FAILURE_FATAL="no"
 IPV6INIT="yes"
 IPV6_AUTOCONF="yes"
 IPV6_DEFROUTE="yes"
 IPV6_FAILURE_FATAL="no"
 NAME="eth0"
 UUID="792d6842-221d-5c99-ba98-cddbba4ff263"
 ONBOOT="no"
 HWADDR="00:AA:5D:01:22:2B"
 DNS1="10.15.10.5"
 DOMAIN="bytefreaks.local"
 IPADDR=10.15.10.249
 PREFIX=24
 GATEWAY=10.15.10.1
 PEERDNS=yes
 PEERROUTES=yes
 IPV6_PEERDNS=yes
 IPV6_PEERROUTES=yes
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Device has MAC address X, instead of configured address Y.

Recently, we tried to take a network interface down on a VM, when we executed the command

ifdown eth0

we got the following error:

ERROR    : [/etc/sysconfig/network-scripts/ifdown-eth] Device  has MAC address 00:00:00:00:00:00
 00:45:4D:04:02:36
 00:45:4D:04:02:40, instead of configured address 00:45:4D:16:0B:29. Ignoring.

We used ifconfig eth0 to check the information on the network interfaces which resulted in the following data:

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
 inet 10.1.20.115  netmask 255.255.255.0  broadcast 10.1.20.255
 inet6 fe80::215:5dff:fe01:236  prefixlen 64  scopeid 0x20<link>
 ether 00:45:4d:04:02:36  txqueuelen 1000  (Ethernet)
 RX packets 10103919  bytes 5474528935 (5.0 GiB)
 RX errors 0  dropped 0  overruns 0  frame 0
 TX packets 6541413  bytes 1190276207 (1.1 GiB)
 TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

We saw that the value ether for eth0 was 00:45:4d:04:02:36, which was one of the addresses the warning mentioned that are valid.

Apparently, we had an error in the following configuration file:

/etc/sysconfig/network-scripts/ifcfg-eth0

The value for HWADDR was set to 00:45:4D:16:0B:29 which was wrong (most likely this file was copied here from another source), after we updated the value to 00:45:4d:04:02:36 we were able to use the device normally.


Oracle VirtualBox: Enable eth0 on backtrack4 / enable default ethernet card on backtrack

ifup eth0

*INFO: The default Ethernet device is disabled on boot but it can easily be enabled by just issuing the above command. (You still need to configure it depending on your system’s structure). In order to activate the Ethernet card you need to call the above command from the Terminal.