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)

Writing to files with file descriptors

We have already seen some uses of file descriptors in previous chapters, for example, 0, 1, and 2 (stdin, stdout, and stderr). But in this recipe, we will use file descriptors to write text to files from a program.

Knowing how to use file descriptors to write to files both gives you a deeper understanding of the system and enables you to do some low-level stuff.

Getting ready

For this recipe, you only need what is listed under the Technical requirements section.

How to do it…

Here we will write a small program that writes text to a file:

  1. Write the following code in a file and save it as fd-write.c. The program takes two arguments: a string and a filename. To write to a file using file descriptors, we must first open the file with the open() system call. The open() system call returns a file descriptor, which is an integer. We then use that file descriptor (the integer) with the write() system call. We have already...