Linux Bible, 10th Edition

CHAPTER 25Securing Linux on a Network

 

IN THIS CHAPTER

• Managing network services
• Controlling access to network services
• Implementing firewalls

Setting up your Linux system on a network, especially a public network, creates a whole new set of challenges when it comes to security. The best way to secure your Linux system is to keep it off all networks. However, that is rarely a feasible option.

Entire books have been filled with information on how to secure a computer system on a network. Many organizations hire full-time computer security administrators to watch over their network-attached Linux systems. Therefore, think of this chapter as a brief introduction to securing Linux on a network.

Auditing Network Services

Most Linux systems used for large enterprises are configured as servers that, as the name implies, offer services to remote clients over a network. A network service is any task that the computer performs requiring it to send and receive information over the network using some predefined set of rules. Routing email is a network service, as is serving web pages.

A Linux server has the potential to provide thousands of services. Many of them are listed in the /etc/services file. Consider the following sections from the /etc/services file:

• $ cat /etc/services
  # /etc/services:
  # $Id: services,v 1.55 2013/04/14 ovasik Exp $
  #
  # Network services, Internet style
  # IANA services version: last updated 2013-04-10
  #
  # Note that it is presently the policy of IANA ...