Allow http through firewall on CentOS 7

$ firewall-cmd --permanent --zone=public --add-service=http
$ firewall-cmd --reload

Missing ifconfig on recent Fedora-based distributions (RHEL, CentOS, Scientific Linux)

In the absence of ifconfig, use the following to reveal your IP address:
$ ip addr

RHEL yum update

If you know your way around CentOS or Fedora and find yourself in front of a new RHEL system, you might find you're unable to run yum update or yum install due to subscription errors.

You need a redhat.com account for this to work, simply issue:
$ sudo subscription-manager register
Follow the prompts and then:
$ sudo subscription-manager attach

You'll then be able to yum update to your heart's content.