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)

Investigating TTYs and PTYs and writing to them

In this recipe, we'll learn how to list currently logged-in users, which TTYs they use, and which programs they are running. We'll also learn how to write to those users and terminals. As we'll see in this recipe, we can write to a terminal device just as if it were a file, assuming we have the correct permissions.

Knowing how to write to other terminals deepens understanding of how terminals work and what they are. It also enables you to write some interesting software and, above all, it will make you a better system administrator. It also teaches you about terminal security.

How to do it…

We'll start by investigating the logged-in users; then, we'll learn how to send messages to them:

  1. To make things a bit more interesting, open up three to four terminal windows. If you're not using the X-Window System, log in on multiple TTYs. Or, if you are using a remote server, log in several...