Open file for ethX using vi, type:
If you want to activate eth0 then you will need to edit file of "etc/sysconfig/network-scripts/ifcfg-eth0" and ensure that it is having below section with ONBOOT=yes
Sample config file:
# Intel Corporation 80003ES2LAN Gigabit Ethernet Controller (Copper) DEVICE=eth0 BOOTPROTO=static DHCPCLASS= HWADDR=00:19:B1:2A:BA:B8 IPADDR=xx.xx.xx.xx NETMASK=255.255.255.xx ONBOOT=yes
Save and close the file.
Once done restart networking (by running
service network restart).