The Linux Kernel Module Programming Guide

By Peter Jay Salzman, Michael Burian, and Ori Pomerantz

The Linux Kernel Module Programming Guide was originally written for the 2.2 kernels by Ori Pomerantz. Eventually, Ori no longer had time to maintain the document. After all, the Linux kernel is a fast moving target. Peter Jay Salzman took over maintenance and updated it for the 2.4 kernels. Eventually, Peter no longer had time to follow developments with the 2.6 kernel, so Michael Burian became a co-maintainer to update the document for the 2.6 kernels.

What Is A Kernel Module?

So, you want to write a kernel module. You know C, you've written a few normal programs to run as processes, and now you want to get to where the real action is, to where a single wild pointer can wipe out your file system and a core dump means a reboot.

What exactly is a kernel module? Modules are pieces of code that can be loaded and unloaded into the kernel upon demand. They extend the functionality of the kernel without the need to reboot the system. For example, one type of module is the device driver, which allows the kernel to access hardware connected to the system. Without modules, we would have to build monolithic kernels and add new functionality directly into the kernel image. Besides having larger kernels, this has the disadvantage of requiring us to rebuild and reboot the kernel every time we want new functionality.

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Advanced Linux Programming

By Mark Mitchell, Jeffrey Oldham, and Alex Samuel

GNU/Linux has taken the world of computers by storm.At one time, personal computer users were forced to choose among proprietary operating environments and applications. Users had no way of fixing or improving these programs, could not look “under the hood,” and were often forced to accept restrictive licenses. GNU/Linux and other open source systems have changed that—now PC users, administrators, and developers can choose a free operating environment complete with tools, applications, and full source code.

A great deal of the success of GNU/Linux is owed to its open source nature. Because the source code for programs is publicly available, everyone can take part in development, whether by fixing a small bug or by developing and distributing a complete major application.This opportunity has enticed thousands of capable developers worldwide to contribute new components and improvements to GNU/Linux, to the point that modern GNU/Linux systems rival the features of any proprietary system, and distributions include thousands of programs and applications spanning many CDROMs or DVDs.

The success of GNU/Linux has also validated much of the UNIX philosophy. Many of the application programming interfaces (APIs) introduced in AT and T and BSD UNIX variants survive in Linux and form the foundation on which programs are built.The UNIX philosophy of many small command line-oriented programs working together is the organizational principle that makes GNU/Linux so powerful. Even when these programs are wrapped in easy-to-use graphical user interfaces, the underlying commands are still available for power users and automated scripts. A powerful GNU/Linux application harnesses the power of these APIs and commands in its inner workings. GNU/Linux’s APIs provide access to sophisticated features such as interprocess communication, multithreading, and high-performance networking.And many problems can be solved simply by assembling existing commands and programs using simple scripts.

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The Art of Unix Programming

By Eric Steven Raymond

You should read this book if you are an experienced Unix programmer who is often in the position of either educating novice programmers or debating partisans of other operating systems, and you find it hard to articulate the benefits of the Unix approach.

You should read this book if you are a C, C++, or Java programmer with experience on other operating systems and you are about to start a Unix-based project.

You should read this book if you are a Unix user with novice-level up to middle-level skills in the operating system, but little development experience, and want to learn how to design software effectively under Unix.

You should read this book if you are a non-Unix programmer who has figured out that the Unix tradition might have something to teach you. We believe you're right, and that the Unix philosophy can be exported to other operating systems. So we will pay more attention to non-Unix environments (especially Microsoft operating systems) than is usual in a Unix book; and when tools and case studies are portable, we say so.

You should read this book if you are an application architect considering platforms or implementation strategies for a major general-market or vertical application. It will help you understand the strengths of Unix as a development platform, and of the Unix tradition of open source as a development method.

You should not read this book if what you are looking for is the details of C coding or how to use the Unix kernel API. There are many good books on these topics; Advanced Programming in the Unix Environment [Stevens92] is classic among explorations of the Unix API, and The Practice of Programming [Kernighan-Pike99] is recommended reading for all C programmers (indeed for all programmers in any language).

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Bourne / Bash shell scripting tutorial

By Steve Parker

A Bourne Shell Programming/Scripting Tutorial for learning about using the Unix shell. Learn Linux / Unix shell scripting by example along with the theory. We'll have you mastering Unix shell scripting in no time!

This tutorial is written to help people understand some of the basics of shell script programming, and hopefully to introduce some of the possibilities of simple but powerful programming available under the bourne shell. As such, it has been written as a basis for one-on-one or group tutorials and exercises, and as a reference for subsequent use.

Steve Bourne, wrote the Bourne shell which appeared in the Seventh Edition Bell Labs Research version of Unix. Many other shells have been written; this particular tutorial concentrates on the Bourne and the Bourne Again shells. Other shells include the Korn Shell (ksh), the C Shell (csh), and variations such as tcsh. This tutorial does not cover those shells. Maybe a future version will cover ksh; I do not intend to write a tutorial for csh, as csh programming is considered harmful.

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C-shell Cookbook

By Malcolm J. Currie

This cookbook describes the fundamentals of writing scripts using the UNIX C shell. It shows how to combine Starlink and private applications with shell commands and constructs to create powerful and time-saving tools for performing repetitive jobs, creating data-processing pipelines, and encapsulating useful recipes. The cookbook aims to give practical and reassuring examples to at least get you started without having to consult a UNIX manual. However, it does not offer a comprehensive description of C-shell syntax to prevent you from being overwhelmed or intimidated. The topics covered are: how to run a script, defining shell variables, prompting, arithmetic and string processing, passing information between Starlink applications, obtaining dataset attributes and FITS header information, processing multiple files and filename modification, command-line arguments and options, and loops. There is also a glossary.

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Sed - An Introduction and Tutorial

By Bruce Barnett

Sed is the ultimate stream editor. If that sounds strange, picture a stream flowing through a pipe. Okay, you can't see a stream if it's inside a pipe. That's what I get for attempting a flowing analogy. You want literature, read James Joyce.

Anyhow, sed is a marvelous utility. Unfortunately, most people never learn its real power. The language is very simple, but the documentation is terrible. The Solaris on-line manual pages for sed are five pages long, and two of those pages describe the 34 different errors you can get. A program that spends as much space documenting the errors than it does documenting the language has a serious learning curve.

Do not fret! It is not your fault you don't understand sed. I will cover sed completely. But I will describe the features in the order that I learned them. I didn't learn everything at once. You don't need to either.

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POSIX and Korn Shell

This tutorial describes the POSIX Shell (/bin/posix/sh) and the Korn Shell (/bin/ksh). POSIX Shell is based on the standard, IEEE P1003.2. Korn Shell is the command interpreter (human interface) written by David Korn at AT&T Bell Laboratories. The tutorial covers the similarities and the differences between these two shells, as well as the new features introduced in the POSIX Shell.

This tutorial addresses new users who are just learning shells, as well as advanced users who are Bourne and C Shell experts. New users should read all of this tutorial. However, at the beginning of each chapter advanced users will be directed to only the areas they need to concentrate on to come up to speed quickly. Both classes of users should finish reading this section.

The kernel is the supervisory part of the HP-UX operating system that keeps track of and assigns system resources to each user. It also coordinates I/O operation, and performs other software functions. A shell is a program that acts as an interface between the system and each user. The shell interprets user commands, then performs system calls to the kernel or loads and runs programs according to the commands given by the user.

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Easy Shell Scripting

By Blessen Cherian

Introduction

Shell scripting can be defined as a group of commands executed in sequence. Let's start by describing the steps needed to write and execute a shell script:

Step 1: Open the file using an editor (e.g., "vi" or "pico".)

vi Firstshellscript.sh

Step 2: All shell scripts should begin with "#!/bin/bash" or whatever other shell you prefer. This line is called the shebang, and although it looks like a comment, it's not: it notifies the shell of the interpreter to be used for the script. The provided path must be an absolute one (you can't just use "bash", for example), and the shebang must be located on the first line of the script without any preceding space.

Step 3: Write the code that you want to develop. Our first shell script will be the usual "Hello World" routine, which we'll place in a file called 'Firstshellscript.sh'.

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Writing Shell Scripts

By William Shotts, Jr.

Here is where the fun begins

With the thousands of commands available for the command line user, how can you remember them all? The answer is, you don't. The real power of the computer is its ability to do the work for you. To get it to do that, we use the power of the shell to automate things. We write scripts.

Scripts are collections of commands that are stored in a file. The shell can read this file and act on the commands as if they were typed at the keyboard. In addition to the things you have learned so far, the shell also provides a variety of useful programming features to make your scripts truly powerful.

What are scripts good for? A wide range of tasks can be automated. Here are some of the things I automate with scripts:

• A script gathers up all the files (over 2200) in this site on my computer and transmits them to my web server.
• The SuperMan pages are built entirely by a script.
• Every Friday night, all my computers copy their files to a "backup server" on my network. This is performed by a script.
• A script automatically gets the current updates from my Linux vendor and maintains a repository of vital updates. It sends me an email message with a report of tasks that need to be done.

As you can see, scripts unlock the power of your Linux machine. So let's have some fun!

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Programming the UNIX/linux Shell

By Claude Cantin

Bourne - C shell comparisons
A Bourne Shell Script is a file containing a series of Bourne Shell commands, as well as control structures such as if statements, while loops, etc. Parameters can be passed to the script and data can be read from the keyboard.

Bourne shell scripts are usually Algol-66 look-alikes, whereas C shell scripts look more like C program constructs.

The C shell is slower to start execution (as it looks in the .cshrc file EVERY TIME it is called) and produces a hash table of all paths for faster execution. The Bourne shell is slower, but starts executing immediately.

For that reason, short scripts are executed much faster in the Bourne Shell than the C shell (this is noticeable for small SLOW machines; with systems running at 30 to 130 MIPS/CPU, the difference in speed is almost insignificant). Large scripts should most likely be written in a compiled language--preferably C--because compiled code executes much faster than interpreted code.

Many features of the Bourne shell are also found in the C shell. Parameters are interpreted in the same way. Variable assignments are very similar. UNIX commands are exactly the same. Control structures and comparisons differ the most.

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Learning the Shell

By William Shotts, Jr.


What is "the shell"?

Simply put, the shell is a program that takes your commands from the keyboard and gives them to the operating system to perform. In the old days, it was the only user interface available on a Unix computer. Nowadays, we have graphical user interfaces (GUIs) in addition to command line interfaces (CLIs) such as the shell.

On most Linux systems a program called bash (which stands for Bourne Again SHell, an enhanced version of the original Bourne shell program, sh, written by Steve Bourne) acts as the shell program. There are several additional shell programs available on a typical Linux system. These include: ksh, tcsh and zsh.

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THE Unix SHELL GUIDE

by Norman J. Buchanan and Douglas M. Gingrich

What is a shell? A shell is a command interpreter. While this is certainly true it likely doesn't enlighten the reader any further. A shell is an entity that takes input from the user and deals with the computer rather than have the user deal directly with the computer. If the user had to deal directly with the computer he would not get much done as the computer only understands strings of 1's and 0's. While this is a bit of a misrepresentation of what the shell actually does (the idea of an operating system is neglected) it provides a rough idea that should cause the reader to be grateful that there is such a thing as a shell. A good way to view a shell is as follows. When a person drives a car, that person doesn't have to actually adjust every detail that goes along with making the engine run, or the electronic system controlling all of the engine timing and so on. All the user (or driver in this example) needs to know is that D means drive and that pressing accelerator pedal will make the car go faster or slower. The dashboard would also be considered part of the the shell since pertinent information relating to the user's involvement in operating the car is displayed there. In fact any part of the car that the user has control of during operation of the car would be considered part of the shell. I think the idea of what a shell is coming clear now. It is a program that allows the user to use the computer without him having to deal directly with it. It is in a sense a protective shell that prevents the user and computer from coming into contact with one another.

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Learning the Korn Shell

by Bill Rosenblatt and Arnold Robbins

The long, tortuous history of the Unix operating system has resulted in systems with all kinds of permutations and combinations of features. This means that whenever you walk up to an unfamiliar Unix system, you need to find out certain things about it in order to use it properly. And even on a given system, you may have a number of choices you can make about what features you want to use.

The most important such decision -- if you get to make it -- is what shell to use. "Shell" is Unix jargon for the program that allows you to communicate with the computer by entering commands and getting responses. The shell is completely separate from the Unix operating system per se; it's just a program that runs on Unix. With other systems such as MS-DOS, Microsoft Windows, Macintosh, OpenVMS, and VM/CMS, the command interpreter or user interface is an integral part of the operating system.

Nowadays there are dozens of different shells floating around, ranging from the original standard, the Bourne shell, to menu-based and graphical interfaces. The most important shells have been the Bourne shell, the C shell, and the Korn shell -- the subject of this book.

Specifically, this book describes the 1993 version of the Korn shell. The 1993 version is distributed with the three major commercial versions of Unix: Solaris, HP-UX, and AIX, albeit as part of the Common Desktop Environment (CDE), in /usr/dt/bin/dtksh. The 1988 version is also available on modern Unix systems, usually as /usr/bin/ksh.

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GAWK: Effective AWK Programming: A User's Guide for GNU Awk

By Arnold D. Robbins

Several kinds of tasks occur repeatedly when working with text files. You might want to extract certain lines and discard the rest. Or you may need to make changes wherever certain patterns appear, but leave the rest of the file alone. Writing single-use programs for these tasks in languages such as C, C++, or Pascal is time-consuming and inconvenient. Such jobs are often easier with awk. The awk utility interprets a special-purpose programming language that makes it easy to handle simple data-reformatting jobs.

The GNU implementation of awk is called gawk; it is fully compatible with the System V Release 4 version of awk. gawk is also compatible with the POSIX specification of the awk language. This means that all properly written awk programs should work with gawk. Thus, we usually don't distinguish between gawk and other awk implementations.

Using awk allows you to:

• Manage small, personal databases
• Generate reports
• Validate data
• Produce indexes and perform other document preparation tasks
• Experiment with algorithms that you can adapt later to other computer languages
  

In addition, gawk provides facilities that make it easy to:

• Extract bits and pieces of data for processing
• Sort data
• Perform simple network communications
  

This Web page teaches you about the awk language and how you can use it effectively. You should already be familiar with basic system commands, such as cat and ls,1 as well as basic shell facilities, such as input/output (I/O) redirection and pipes.

Implementations of the awk language are available for many different computing environments. This Web page, while describing the awk language in general, also describes the particular implementation of awk called gawk (which stands for “GNU awk”). gawk runs on a broad range of Unix systems, ranging from 80386 PC-based computers up through large-scale systems, such as Crays. gawk has also been ported to Mac OS X, MS-DOS, Microsoft Windows (all versions) and OS/2 PCs, Atari and Amiga microcomputers, BeOS, Tandem D20, and VMS.

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Sams Teach Yourself Shell Programming in 24 Hours

By Sriranga Veeraraghavan

In recent years, the UNIX operating system has seen a huge boost in its popularity, especially with the emergence of Linux. For programmers and users of UNIX, this comes as no surprise: UNIX was designed to provide an environment that's powerful yet easy to use.

One of the main strengths of UNIX is that it comes with a large collection of standard programs. These programs perform a wide variety of tasks from listing your files to reading email. Unlike other operating systems, one of the key features of UNIX is that these programs can be combined to perform complicated tasks and solve your problems.

One of the most powerful standard programs available in UNIX is the shell. The shell is a program that provides you with a consistent and easy-to-use environment for executing programs in UNIX. If you have ever used a UNIX system, you have interacted with the shell.

The main responsibility of the shell is to read the commands you type and then ask the UNIX kernel to perform these commands. In addition to this, the shell provides sophisticated programming constructs that enable you to make decisions, repeatedly execute commands, create functions, and store values in variables.

This book concentrates on the standard UNIX shell called the Bourne shell. When Dennis Ritche and Ken Thompson were developing much of UNIX in the early 1970s, they used a very simple shell. The first real shell, written by Stephen Bourne, appeared in the mid 1970s. The original Bourne shell has changed slightly over the years; some features were added and others were removed, but its syntax and its resulting power have remained the same.

The most attractive feature of the shell is that it enables you to create scripts. Scripts are files that contain a list of commands you want to run. Because every script is contained in a file and every file has a name, scripts enable you to combine existing programs to create completely new programs that solve your problems. This book teaches you how to create, execute, modify, and debug shell scripts quickly and easily. After you get used to writing scripts, you will find yourself solving more and more problems with them.

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GNU Bash Reference Manual

Chet Ramey, Case Western Reserve University
Brian Fox, Free Software Foundation
Edited for publication by Brian Gough

Bash is the shell, or command language interpreter, for the GNU operating system. The name is an acronym for the ‘Bourne-Again SHell’, a pun on Stephen Bourne, the author of the direct ancestor of the current Unix shell sh, which appeared in the Seventh Edition Bell Labs Research version of Unix.

Bash is largely compatible with sh and incorporates useful features from the Korn shell ksh and the C shell csh. It is intended to be a conformant implementation of the IEEE POSIX Shell and Tools portion of the IEEE POSIX specification (IEEE Standard 1003.1). It offers functional improvements over sh for both interactive and programming use.

While the GNU operating system provides other shells, including a version of csh, Bash is the default shell. Like other GNU software, Bash is quite portable. It currently runs on nearly every version of Unix and a few other operating systems--independently-supported ports exist for MS-DOS, OS/2, and Windows platforms.

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Bash Guide for Beginners

By Machtelt Garrels

The primary reason for writing this document is that a lot of readers feel the existing HOWTO to be too short and incomplete, while the Bash Scripting guide is too much of a reference work. There is nothing in between these two extremes. I also wrote this guide on the general principal that not enough free basic courses are available, though they should be.

This is a practical guide which, while not always being too serious, tries to give real-life instead of theoretical examples. I partly wrote it because I don't get excited with stripped down and over-simplified examples written by people who know what they are talking about, showing some really cool Bash feature so much out of its context that you cannot ever use it in practical circumstances. You can read that sort of stuff after finishing this book, which contains exercises and examples that will help you survive in the real world.

From my experience as UNIX/Linux user, system administrator and trainer, I know that people can have years of daily interaction with their systems, without having the slightest knowledge of task automation. Thus they often think that UNIX is not userfriendly, and even worse, they get the impression that it is slow and old-fashioned. This problem is another one that can be remedied by this guide.

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