By default, the new Centos 6.0 distro performs a “minimal” install, as I mentioned last time. This is good because you end up with a very small footprint O/S (no Gnome, for example), leaving the server more resources to run the things you actually use servers for (like Oracle).
The downside to it, however, is that a feature of Red Hat Enterprise Server 6 (and therefore of all its clones -so this stuff applies to Scientific Linux 6, too) is that it defaults to managing your network connections with NetworkManager, which isn’t actually installed as part of a minimal install. The net result (no pun intended) is that your network doesn’t work when you first boot into your new, slimline O/S.
The fix is to run the command system-config-network-tui, which allows you to specify a fixed IP address manually. In Centos 6, however, even this tool is not installed as part of a minimal install (I guess they took the word ‘minimal’ literally), so you’ll end up having to edit by hand the /etc/sysconfig/network-scripts/ifcfg-eth0 file.
You’ll need to end up with something looking like this:
IPADDR=192.168.0.33 BOOTPROTO=none NETMASK=255.255.255.0 GATEWAY=192.168.0.1 DNS1=192.168.0.1 DNS2=192.168.0.2 USERCTL=yes
Obviously, you replace those specific IP addresses with whatever suits your local environment. The USERCTL=yes line is optional: it lets non-root users control the interface. Once the file has the appropriate entries, a reboot will do to make the new settings take effect.
In Scientific Linux 6, the system-config-network-tui tool exists, so you could use that… or you can achieve all these edits with the nano text editor. The Centos 6 minimal install is less forgiving, however, and you’ll have to use vi (because nano is not installed as part of its minimal install option).