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)

Returning an error value

Even though human-readable error messages are important, we must not forget to return a value to the shell that indicates an error. We have already seen that returning 0 means that everything is okay, while returning something else (most of the time, 1) means that some kind of error did occur. However, we can return more specific values if we want so that other programs relying on our program can read those numbers. For example, we can actually return the errno variable since it is just an integer. All the macros we have seen, such as EACCES and ENOENT, are integers (13 and 2 for EACCES and ENOENT, respectively).

In this recipe, we will learn how to return the errno numbers to the shell to provide more specific information.

Getting ready

The same set of programs mentioned in the previous recipe apply to this recipe.

How to do it…

In this recipe, we will make the seventh version of our simple-touch program. Let's get started: