IN THIS APPENDIX
Security is a major part of the foundation of any system that is not totally cut off from other machines and users. Some aspects of security have a place even on isolated machines. Examples are periodic system backups, BIOS or power-on passwords, and self-locking screensavers.
A system that is connected to the outside world requires other mechanisms to secure it: tools to check files (tripwire), audit tools (tiger/cops), secure access methods (kerberos/ssh), services that monitor logs and machine states (swatch/watcher), packet-filtering and routing tools (ipfwadm/iptables/ipchains), and more.
System security has many dimensions. ...