Linux

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 has many distributions, each offering a slightly different approach. Some of the most common Linux distributions include RedHat, 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.

Linux authentication

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.