|1, 2, 4||Basic Unix||
|3||Networking and Firewall||
there is a "Networking Concepts Howto",
a "Packet Filtering Howto" and several tutorials for IP tables at
Some of the documents are available in several languages (including
French and Chinese).
Quick reference for the configuration files; more detailed
HowTo configure DNS.
is an overview of differences between different flavours of Unix.