CentOS 6.5 not bringing up network interface automatically after reboot [ifup eth0]
Ensure that the file /etc/sysconfig/network-scripts/ifcfg-eth0 has the line
ONBOOT="yes"
See 9.2. Interface Configuration Files for details.
Make sure ONBOOT="yes" is set in /etc/sysconfig/network-scripts/ifcfg-eth0 also check that
NetworkManager or network (whichever you use) is started on boot.
chkconfig NetworkManager on or chkconfig network on
Configuration file must have right privileges also:
sudo chmod 0755 /etc/sysconfig/network-scripts/ifcfg-*
At /etc/sysconfig/network can have those lines:
NETWORKING=yes
HOSTNAME=myhostname.mydomain
NETWORKING_IPV6=yes