December 2025
Intermediate to advanced
704 pages
19h 14m
English
Content preview from Ubuntu Linux Bible, 11th Edition
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CHAPTER 25Securing Linux on a Network
Setting up your Linux system on a network, especially a public network, creates a whole new set of challenges when it comes to security. Of course, the best way to secure a computer is to keep it off all networks. However, that’s rarely a workable option.
Entire books have been filled with information on how to secure a computer system on a network. Many organizations hire full-time network security administrators to watch over their network-attached Linux systems. Therefore, think of this chapter as just a brief introduction to the subject.
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# Network services, Internet style## Updated from https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml .## New ports will be added on request if they have been officially ...
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