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)

Implementing a signal handler

In the previous recipe, we wrote a simple but functional daemon. However, there are some problems with it; for example, the PID file isn't removed when the daemon is killed. Likewise, the open file stream (/tmp/my-daemon-is-alive.txt) isn't closed when the daemon is killed. A proper daemon should clean up after itself when it exits.

To be able to clean up on exit, we need to implement a signal handler. The signal handler should then take care of all the cleanup before the daemon is terminated. We have already seen examples of signal handlers in this chapter, so this concept isn't new.

It's not only daemons that use signal handlers, though. This is a common way of controlling processes, especially processes that don't have a controlling terminal.

Getting ready

You should read the previous recipe before reading this one so that you understand what the daemon does. Other than that, you'll need the programs listed...