Building Secure Servers with Linux

By Michael D. Bauer
First Edition October 2002
Published by O'Reilly

Linux consistently turns up high in the list of popular Internet servers, whether it's for the Web, anonymous FTP, or general services like DNS and routing mail. But security is uppermost on the mind of anyone providing such a service. Any server experiences casual probe attempts dozens of time a day, and serious break-in attempts with some frequency as well. As the cost of broadband and other high-speed Internet connectivity has gone down, and its availability has increased, more Linux users are providing or considering providing Internet services such as HTTP, Anonymous FTP, etc., to the world at large. At the same time, some important, powerful, and popular Open Source tools have emerged and rapidly matured - some of which rival expensive commercial equivalents - making Linux a particularly appropriate platform for providing secure Internet services.

Building Secure Servers with Linux will help you master the principles of reliable system and network security by combining practical advice with a firm knowledge of the technical tools needed to ensure security. The book focuses on the most common use of Linux - as a hub offering services to an organization or the larger Internet - and shows readers how to harden their hosts against attacks. Author Mick Bauer, a security consultant, network architect, and lead author of the popular Paranoid Penguin column in Linux Journal, carefully outlines the security risks, defines precautions that can minimize those risks, and offers recipes for robust security. The book does not cover firewalls, but covers the more common situation where an organization protects its hub using other systems as firewalls, often proprietary firewalls.

System Log Management and Monitoring

Whatever else you do to secure a Linux system, it must have comprehensive, accurate, and carefully watched logs. Logs serve several purposes. First, they help us troubleshoot virtually all kinds of system and application problems. Second, they provide valuable early-warning signs of system abuse. Third, after all else
fails (whether that means a system crash or a system compromise), logs can provide us with crucial forensic data. This chapter is about making sure your system
processes and critical applications log the events and states you're interested in and dealing with this data once it's been logged. The two logging tools we'll cover are syslog and the more powerful Syslog-ng ("syslog new generation"). In the monitoring arena, we'll discuss Swatch (the Simple Watcher), a powerful Perl script that monitors logs in real time and takes action on specified events.

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