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)

Creating a more modern daemon for systemd

Daemons that are handled by systemd don't need to fork or close their file descriptors. Instead, it's advised to use standard output and standard error to write the daemon's logs to the journal. The journal is systemd's logging facility.

In this recipe, we'll write a new daemon, one that doesn't fork and leaves stdin, stdout, and stderr open. It will also write messages to standard output every 30 seconds (instead of to the /tmp/my-daemon-is-alive.txt file, as before). This kind of daemon is sometimes referred to as a new-style daemon. The old forking type, for example, my-daemon-v2.c, is referred to as a SysV-style daemon. SysV was the name of the init system before systemd.

Getting ready

For this recipe, you'll only need what's listed in the Technical requirements section of this chapter.

How to do it...

In this recipe, we'll write a new-style daemon:

  1. This program is a bit...