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)

Replacing the program in a process with execl()

At the beginning of this chapter, we saw how getty gets replaced by login when a user logs in. In this recipe, we will write a small program that does exactly that—replaces its program with a new one. The system call for this is called execl().

Knowing how to use execl() enables you to write programs that execute new programs inside the existing process. It also enables you to start a new program in a spawned process. When we start a new process, we probably want to replace that copy with a new program. So, understanding execl() is paramount.

Getting ready

You will need to have read the first three recipes in this chapter to understand this one fully. The other requirements for this recipe are mentioned in the Technical requirements section of this chapter; for example, you'll need the pstree tool.

You will also need two terminals or two terminal windows for this recipe. In one of these terminals, we will be running...