Linux Security HOWTO


This document is a general overview of security issues that face the administrator of Linux systems. It covers general security philosophy and a number of specific examples of how to better secure your Linux system from intruders. Also included are pointers to security-related material and programs. Improvements, constructive criticism, additions and corrections are gratefully accepted. Please mail your feedback to both authors, with "Security HOWTO" in the subject.

Table of Contents
Physical Security
Local Security
Files and File system Security
Password Security and Encryption
Kernel Security
Network Security
Security Preparation (before you go on-line)
What To Do During and After a Breakin
Security Sources
Frequently Asked Questions


This document covers some of the main issues that affect Linux security. General philosophy and net-born resources are discussed.

A number of other HOWTO documents overlap with security issues, and those documents have been pointed to wherever appropriate.

This document is not meant to be a up-to-date exploits document. Large numbers of new exploits happen all the time. This document will tell you where to look for such up-to-date information, and will give some general methods to prevent such exploits from taking place.

New Versions of this Document

New versions of this document will be periodically posted to comp.os.linux.answers. They will also be added to the various sites that archive such information, including:

The very latest version of this document should also be available in various formats from:


All comments, error reports, additional information and criticism of all sorts should be directed to:


Note: Please send your feedback to both authors. Also, be sure and include "Linux" "security", or "HOWTO" in your subject to avoid Kevin's spam filter.


No liability for the contents of this document can be accepted. Use the concepts, examples and other content at your own risk. Additionally, this is an early version, possibly with many inaccuracies or errors.

A number of the examples and descriptions use the RedHat(tm) package layout and system setup. Your mileage may vary.

As far as we know, only programs that, under certain terms may be used or evaluated for personal purposes will be described. Most of the programs will be available, complete with source, under GNU terms.

Copyright Information

This document is copyrighted (c)1998-2000 Kevin Fenzi and Dave Wreski, and distributed under the following terms:

  • Linux HOWTO documents may be reproduced and distributed in whole or in part, in any medium, physical or electronic, as long as this copyright notice is retained on all copies. Commercial redistribution is allowed and encouraged; however, the authors would like to be notified of any such distributions.

  • All translations, derivative works, or aggregate works incorporating any Linux HOWTO documents must be covered under this copyright notice. That is, you may not produce a derivative work from a HOWTO and impose additional restrictions on its distribution. Exceptions to these rules may be granted under certain conditions; please contact the Linux HOWTO coordinator at the address given below.

  • If you have questions, please contact Tim Bynum, the Linux HOWTO coordinator, at