Book Image

Linux System Programming Techniques

By : Jack-Benny Persson
5 (1)
Book Image

Linux System Programming Techniques

5 (1)
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.

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Table of Contents (14 chapters)
Preface
Preface
Who this book is for
What this book covers
To get the most out of this book
Code in Action
Download the color images
Conventions used
Sections
Get in touch
Reviews
1
Chapter 1: Getting the Necessary Tools and Writing Our First Linux Programs
Chapter 1: Getting the Necessary Tools and Writing Our First Linux Programs
Technical requirements
Installing GCC and GNU Make
Installing GDB and Valgrind
Writing a simple C program for Linux
Writing a program that parses command-line options
Looking up information in the built-in manual page
Searching the manual for information
Free Chapter
2
Chapter 2: Making Your Programs Easy to Script
Chapter 2: Making Your Programs Easy to Script
Technical requirements
Return values and how to read them
Exiting a program with a relevant return value
Redirecting stdin, stdout, and stderr
Connecting programs using pipes
Writing to stdout and stderr
Reading from stdin
Writing a pipe-friendly program
Redirecting the result to a file
Reading environment variables
3
Chapter 3: Diving Deep into C in Linux
Chapter 3: Diving Deep into C in Linux
Technical requirements
Linking against libraries using GCC
Changing C standards
Using system calls – and when not to use them
Getting information about Linux- and Unix-specific header files
Defining feature test macros
Looking at the four stages of compilation
Compiling with Make
Writing a generic Makefile with GCC options
Writing a simple Makefile
Writing a more advanced Makefile
4
Chapter 4: Handling Errors in Your Programs
Chapter 4: Handling Errors in Your Programs
Technical requirements
Why error handling is important in system programming
Handling some common errors
Error handling and errno
Handling more errno macros
Using errno with strerror()
Using errno with perror()
Returning an error value
5
Chapter 5: Working with File I/O and Filesystem Operations
Chapter 5: Working with File I/O and Filesystem Operations
Technical requirements
Reading inode information and learning the filesystem
Creating soft links and hard links
Creating files and updating the timestamp
Deleting files
Getting access rights and ownership
Setting access rights and ownership
Writing to files with file descriptors
Reading from files with file descriptors
Writing to files with streams
Reading from files with streams
Reading and writing binary data with streams
Moving around inside a file with lseek()
Moving around inside a file with fseek()
6
Chapter 6: Spawning Processes and Using Job Control
Chapter 6: Spawning Processes and Using Job Control
Technical requirements
Exploring how processes are created
Using job control in Bash
Controlling and terminating processes using signals
Replacing the program in a process with execl()
Forking a process
Executing a new program in a forked process
Starting a new process with system()
Creating a zombie process
Learning about what orphans are
Creating a daemon
Implementing a signal handler
7
Chapter 7: Using systemd to Handle Your Daemons
Chapter 7: Using systemd to Handle Your Daemons
Technical requirements
Getting to know systemd
Writing a unit file for a daemon
Enabling and disabling a service – and starting and stopping it
Creating a more modern daemon for systemd
Making the new daemon a systemd service
Reading the journal
8
Chapter 8: Creating Shared Libraries
Chapter 8: Creating Shared Libraries
Technical requirements
The what and why of libraries
Creating a static library
Using a static library
Creating a dynamic library
Installing the dynamic library on the system
Using the dynamic library in a program
Compiling a statically linked program
9
Chapter 9: Terminal I/O and Changing Terminal Behavior
Chapter 9: Terminal I/O and Changing Terminal Behavior
Technical requirements
Viewing terminal information
Changing terminal settings with stty
Investigating TTYs and PTYs and writing to them
Checking if it's a TTY
Creating a PTY
Disabling echo for password prompts
Reading the terminal size
10
Chapter 10: Using Different Kinds of IPC
Chapter 10: Using Different Kinds of IPC
Technical requirements
Using signals for IPC – building a client for the daemon
Communicating with a pipe
FIFO – using it in the shell
FIFO – building the sender
FIFO – building the receiver
Message queues – creating the sender
Message queues – creating the receiver
Communicating between child and parent with shared memory
Using shared memory between unrelated processes
Unix socket – creating the server
Unix socket – creating the client
11
Chapter 11: Using Threads in Your Programs
Chapter 11: Using Threads in Your Programs
Technical requirements
Writing your first threaded program
Reading return values from threads
Causing a race condition
Avoiding race conditions with mutexes
Making the mutex program more efficient
Using condition variables
12
Chapter 12: Debugging Your Programs
Chapter 12: Debugging Your Programs
Technical requirements
Starting GDB
Stepping inside a function with GDB
Investigating memory with GDB
Modifying variables during runtime
Using GDB on a program that forks
Debugging programs with multiple threads
Finding a simple memory leak with Valgrind
Finding buffer overflows with Valgrind
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13
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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...
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End of Chapter 7
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