How do I secure my unix box?

This is a very complicated question.

While I would like for this section to be definitive and one-stop, it won't be. Don't consider this the be-all and end-all in advice in system security. This section is new, so it won't contain much initially, but even as it grows I will not remove this warning. Suggestions are always welcome.

There's a very good HOWTO on security. See http://www.tldp.org/HOWTO/Security-HOWTO/index.html or, you can try /usr/doc/HOWTO/Security-HOWTO instead). Another good reference is the Linux Security Administrators Guide.