A command-line network intrusion detection system

Snort lets you protect your network from intruders with a customizable ruleset.

Snort [1] is one of the oldest and most reliable network intrusion detection systems. Founded in 1998 by Martin Roesch, then the CTO of Sourcefire, Snort quickly became so popular that in 2009 InfoWorld declared it one of the top 36 pieces of free software [2]. Like the definitions in a virus detector, Snort relies on a series of rules to detect all known means of compromising a system. It is not difficult to install, but it requires preparation, and, the more customization, the more time-consuming your installation will be. What follows are instructions for a minimal installation for Debian-like distributions, which should be good enough for many users, especially on standalone machines.

To get the very latest protection, install Snort from source [3], using the usual ./configure, make, and install commands. Most distributions also offer a package, although the package is often older than the latest version. However, in a mature application such as Snort, the differences between versions are apt to be minimal, and the rules you install are probably more important. Whichever version you use, you might want to create a Snort group and user solely for running the app, just for added protection. In addition, before installation, gather the necessary information (Figure 1) by running:

ip a

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