When installing a minimal CentOS 6 system, minimal really, really means minimal. After a reboot the network interfaces do not start, so network connectivity is non existing.
Looking into that I noticed that the file
/etc/sysconfig/network-scripts/ifcfg-eth0 contained
DEVICE=eth0
HWADDR=11:22:33:44:55:66
NM_CONTROLLED=yes
ONBOOT=no
BOOTPROTO=dhcp
TYPE=Ethernet
USERCTL=no
PEERDNS=yes
IPV6INIT=no
The lines that mess things up are NM_CONTROLLED=yes meaning the interfaces
are managed with NetworkManager, which isn’t actually installed as part of a
minimal install. You want a minimal install, you get a minimal install. And
ONBOOT=no, meaning “do not start the interface on boot”. How stupid is
that!
The trick is to run something like system-config-network-tui to set the IP
addresses manually, but as you might imagine, that’s not installed either.
So you best edit /etc/sysconfig/network-scripts/ifcfg-eth0 by hand and set it
to:
DEVICE=eth0
HWADDR=11:22:33:44:55:66
NM_CONTROLLED=no
ONBOOT=yes
BOOTPROTO=none
TYPE=Ethernet
USERCTL=no
PEERDNS=yes
IPV6INIT=no
IPADDR=192.168.0.1
NETMASK=255.255.255.0
GATEWAY=192.168.0.254
DNS1=192.168.0.254
The USERCTL=... line is optional: If set to yes it lets non-root users
control the interface.
After setting this a service network restart will do the trick.