Book Image

Mastering Embedded Linux Programming - Third Edition

By : Frank Vasquez, Chris Simmonds
5 (3)
Book Image

Mastering Embedded Linux Programming - Third Edition

5 (3)
By: Frank Vasquez, Chris Simmonds

Overview of this book

If you’re looking for a book that will demystify embedded Linux, then you’ve come to the right place. Mastering Embedded Linux Programming is a fully comprehensive guide that can serve both as means to learn new things or as a handy reference. The first few chapters of this book will break down the fundamental elements that underpin all embedded Linux projects: the toolchain, the bootloader, the kernel, and the root filesystem. After that, you will learn how to create each of these elements from scratch and automate the process using Buildroot and the Yocto Project. As you progress, the book will show you how to implement an effective storage strategy for flash memory chips and install updates to a device remotely once it’s deployed. You’ll also learn about the key aspects of writing code for embedded Linux, such as how to access hardware from apps, the implications of writing multi-threaded code, and techniques to manage memory in an efficient way. The final chapters demonstrate how to debug your code, whether it resides in apps or in the Linux kernel itself. You’ll also cover the different tracers and profilers that are available for Linux so that you can quickly pinpoint any performance bottlenecks in your system. By the end of this Linux book, you’ll be able to create efficient and secure embedded devices using Linux.
Table of Contents (27 chapters)
1
Section 1: Elements of Embedded Linux
10
Section 2: System Architecture and Design Decisions
18
Section 3: Writing Embedded Applications
22
Section 4: Debugging and Optimizing Performance

Configuring user accounts

As I have hinted already, it is not good practice to run all programs as root, since if
one program is compromised by an outside attack, then the whole system is at risk.
It is preferable to create unprivileged user accounts and use them where full root is
not necessary.

Usernames are configured in /etc/passwd. There is one line per user, with seven fields of information separated by colons, which are, in order, the following:

  • The login name
  • A hash code used to verify the password or, more usually, an x to indicate that the password is stored in /etc/shadow
  • The user ID
  • The group ID
  • A comment field, often left blank
  • The user's home directory
  • The shell this user will use (optional)

Here is a simple example in which we have user root with UID 0 and user daemon
with UID 1:

root:x:0:0:root:/root:/bin/sh
daemon:x:1:1:daemon:/usr/sbin:/bin/false

Setting the shell for user daemon to /bin/false ensures that any attempt...