For a nice VM I needed a Linux server, but no need for a GUI, so went for CentOS.

Installed fine, but no networking. How do I install that? Turns out, it is installed, just disabled by default:

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

Find the line ONBOOT and change to yes:

DEVICE=eth0
HWADDR=00:00:00:00:00:00:00 TYPE=ETHERNET
UUID=some guid string
ONBOOT=yes
NM_CONTROLLED=yes
BOOTPROTO=dhcp

Then just restart networking at you should be up and running:

service network restart

Test by entering ifconfig and you should see the loopback address.

If you need to install Guest Additions on VirtualBox:

yum update
yum install gcc make kernel-devel
mkdir /media/cdrom
mount /dev/scd0 /media/cdrom
sh /media/cdrom/VBoxLinuxAdditions.run