Securing Your Linux Installation

By Joshua Erdman
Digital Foundation, inc.

I by no means claim that I am a Linux Security Expert, but I have picked up a trick or two that really help to secure a Linux box without having to go through a ridiculous amount of confusion and frustration.

The first step is to check out what packages and services you have installed. There are a few that you definitely should install to protect your system. These are and SSH Daemon (this is like secure telnet) and IPTables (a firewall).

The next thing to check are all the packages you should not install/start:

1. TFTP - Trivial FTP (FTP without the need of a password)
2. Telnet - In Case if you didn't know, telnet is all clear text.  Use SSH isntead
3. Any services that you do not need. If your server is not hosting a website be sure that apache is not running.

SSH

Open your SSH Daemon config file:
  /etc/ssh/sshd_config
and search for PermitRootLogin. Uncomment this line and change the value to 'no'. By it's name you can guess what this does. Now for root access the user must first log in with a regular user account and then use the command:

su --login root

This requires 2 levels of authentication.

IPTables

There is so much on IPTables it should be its own article. For now use the policy that everything is forbidden by default and then you only allow the access you need. Another really good idea is using gShield. It is a program that has all kinds of security settings and you do not have to be a network pro to get a decent firewall set up.

Article last reviewed: 09/27/2006

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