Book Image

Linux System Programming Techniques

By : Jack-Benny Persson
Book Image

Linux System Programming Techniques

By: Jack-Benny Persson

Overview of this book

Linux is the world's most popular open source operating system (OS). Linux System Programming Techniques will enable you to extend the Linux OS with your own system programs and communicate with other programs on the system. The book begins by exploring the Linux filesystem, its basic commands, built-in manual pages, the GNU compiler collection (GCC), and Linux system calls. You'll then discover how to handle errors in your programs and will learn to catch errors and print relevant information about them. The book takes you through multiple recipes on how to read and write files on the system, using both streams and file descriptors. As you advance, you'll delve into forking, creating zombie processes, and daemons, along with recipes on how to handle daemons using systemd. After this, you'll find out how to create shared libraries and start exploring different types of interprocess communication (IPC). In the later chapters, recipes on how to write programs using POSIX threads and how to debug your programs using the GNU debugger (GDB) and Valgrind will also be covered. By the end of this Linux book, you will be able to develop your own system programs for Linux, including daemons, tools, clients, and filters.
Table of Contents (14 chapters)

Moving around inside a file with lseek()

In this recipe, we'll learn how to move around inside a file with lseek(). This function operates on file descriptors, so please note that we are now working with file descriptors, not streams. With lseek(), we can move around (or seek) freely inside a file descriptor. Doing so can be handy if we only want to read a specific part of a file or we want to go back and read some data twice and so on.

In this recipe, we will modify our previous program, called fd-read.c, to specify where we want to start reading. We also make it so that the user can specify how many characters should be read from that position.

Getting ready

To easier understand this recipe, I encourage you to read the recipe named Reading from files with file descriptors in this chapter before reading this one.

How to do it…

The program we will write here will read a file using file descriptors. The user must also set a starting position where the read...