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Who should be reading this document and why should the average Linux user care about security? Those new to Linux, or unfamiliar with the inherent security issues of connecting a Linux system to large networks like Internet should be reading. "Security" is a broad subject with many facets, and is covered in much more depth in other documents, books, and on various sites on the Web. This document is intended to be an introduction to the most basic concepts as they relate to Linux, and as a starting point only.
The above is real, live data from a one week period for my home LAN. Much of the above would seem to be specifically targeted at Linux systems. Many of the targeted "destination" ports are used by well known Linux and Unix services, and all may be installed, and possibly even running, on your system.
The focus here will be on threats that are shared by all Linux users, whether a dual boot home user, or large commercial site. And we will take a few, relatively quick and easy steps that will make a typical home Desktop system or small office system running Linux reasonably safe from the majority of outside threats. For those responsible for Linux systems in a larger or more complex environment, you'd be well advised to read this, and then follow up with additional reading suitable to your particular situation. Actually, this is probably good advice for everybody.
We will assume the reader knows little about Linux, networking, TCP/IP, and the finer points of running a server Operating System like Linux. We will also assume, for the sake of this document, that all local users are "trusted" users, and won't address physical or local network security issues in any detail. Again, if this is not the case, further reading is strongly recommended.
The principles that will guide us in our quest are:
The steps we will be taking to get there are:
If you don't have time to read everything, concentrate on Steps 1, 2, and 3. This is where the meat of the subject matter is. The Appendix has a lot of supporting information, which may be helpful, but may not be necessary for all readers.
Security-Quickstart HOWTO for Linux
Copyright © 2001 Hal Burgiss.
This document is free; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
This document is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You can get a copy of the GNU GPL at at http://www.gnu.org/copyleft/gpl.html.
Many thanks to those who helped with the production of this document.
The author accepts no liability for the contents of this document. Use the concepts, examples and other content at your own risk. As this is a new document, there may be errors and inaccuracies. Hopefully these are few and far between. Corrections and suggestions are welcomed.
This document is intended to give the new user a starting point for securing their system while it is connected to the Internet. Please understand that there is no intention whatsoever of claiming that the contents of this document will necessarily result in an ultimately secure and worry-free computing environment. Security is a complex topic. This document just addresses some of the most basic issues that inexperienced users should be aware of.
The reader is encouraged to read other security related documentation and articles. And to stay abreast of security issues as they evolve. Security is not an objective, but an ongoing process.
The current official version can always be found at http://www.linuxdoc.org/HOWTO/Security-Quickstart-HOWTO/. Pre-release versions can be found at http://feenix.burgiss.net/ldp/quickstart/.
Other formats, including PDF, PS, single page HTML, may be found at the Linux Documentation HOWTO index page: http://linuxdoc.org/docs.html#howto.
Version 1.1: Various corrections, amplifications and numerous mostly small additions. Too many to list. Oh yea, learn to spell Red Hat correctly ;-)
Version 1.0: This is the initial release of this document. Comments welcomed.