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)

Reading the journal

In this recipe, we'll learn how to read the journal. The journal is systemd's logging facility. All messages that a daemon prints to either stdout or stderr gets added to the journal. But we can find more than just the system daemons logs here. There's also the system's boot messages, among other things.

Knowing how to read the journal enables you to find errors in the system and the daemons more easily.

Getting ready

For this recipe, you'll need to have the new-style-daemon service running. If you don't have it running on your system, go back to the previous recipe for information on how to start it.

How to do it...

In this recipe, we'll explore how to read the journal and what kind of information we can find in it. We'll also learn how to follow a particular service's log:

  1. We'll start by examining the logs from our service, new-style-daemon. The -u option stands for unit:
    $> sudo journalctl...