Despite the complexity of operating systems, the basic function and purpose of a network operating system is straightforward: to provide services to the network. The following are some of the most common of these services:
File and print services
Web server services
Firewall and proxy services
Dynamic Host Configuration Protocol (DHCP) and Domain Name System (DNS) services
These are just a few of a large number of services that a network operating system can provide.
The following sections discuss the major operating systems currently in use and how each of them deals with basic services such as authentication, security, and file and print services.
Providing a summary of Linux in a few paragraphs is a difficult task. Unlike other operating systems, each of which has only a single variation, Linux is a freely distributable open source operating system that has many variants called distributions. Each of these distributions offers a slightly different approach to certain aspects of the operating system, such as installation and management utilities. Some of the most common Linux distributions include Red Hat, SuSE, Debian, and Caldera. In light of the many versions of Linux, if a command or an approach is listed in this section and is not available in the version of Linux you are using, you can look for an equivalent command or approach in your version, and you will very likely find one.
People who are used to working on a Windows-based system will no doubt discover that administration on a Linux system is very different. For instance, authentication information such as a list of users is kept in a text file. This file,
/etc/passwd, controls who can and cannot log on to the system.
For a user to log on to the system, a valid username and password combination must be supplied. Both of these pieces of information are case sensitive.