Post-install steps for a new Linux instance, and how to automate them

The way we do this is to use a kickstart/preseed file to install & configure Puppet on our servers during the OS install. Then as long as you've preconfigured your Puppet manifest to do all your initial tasks, it'll happen automatically.

I've got about 5,000 lines worth of Puppet manifest that do what I need. A bit much to be listing in a ServerFault answer.

10. add your user authentication program, such as LDAP, Kerberos, etc.
11. default firewall rules
12. default repositories (such as internal repos)
13. update specified packages/utilities from your repos that may be old on your kickstart image