0 Linux System

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Linux is a popular operating system with system administrators because of its open source code and its flexibility, which allows anyone to modify it. Because of the open source nature of Linux, there are many different versions, known as distributions (or distros). Several of the Linux distributions have become robust commercial operating systems for use on workstations as well as servers. Popular commercial distributions include Red Hat, Debian, Mandrake, and SUSE; some of the most common free versions are Gentoo and Knoppix. Linux’s flexibility and the fact that it’s open source, together with the increase in Linux applications, have made Linux the operating system of choice for many systems. Although Linux has inherently tighter security than Windows operating systems, it also has vulnerabilities that can be exploited. This chapter covers the basics of getting started using Linux as an operating system and knowing how to harden the system to attacks.

Linux is loosely based on Unix, and anyone familiar with working in a Unix environment should be able to use a Linux system. All standard commands and utilities are included on most distros. Many text editors are available inside a Linux system, including vi, ex, pico, jove, and GNU emacs. Many Unix users prefer “simple” editors like vi. But vi has many limitations due to its age, and most modern editors like emacs have gained popularity in recent years. Most of the basic Linux utilities are GNU software, meaning they are freely distributed to the community. GNU utilities also support advanced features that are not found in the standard versions of BSD and UNIX System. However, GNU utilities are intended to remain compatible with BSD.

A shell is a command-line program interface that allows a user to enter commands, and the system executes commands from the user. In addition, many shells provide features like job control, the ability to manage several processes at once, input and output redirection, and a command language for writing shell scripts. A shell script is a program written in the shell’s command language and is similar to an MS-DOS batch file. Many types of shells are available for Linux. The most important difference among shells is the command language. For example, the C SHell (csh) uses a command language similar to the C programming language. The classic Bourne SHell (sh) uses another command language. The choice of a shell is often based on the command language it provides, and determines which features will be available to the user.