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Mastering Embedded Linux Programming

Mastering Embedded Linux Programming

By : Chris Simmonds
4.8 (20)
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Mastering Embedded Linux Programming

Mastering Embedded Linux Programming

4.8 (20)
By: Chris Simmonds

Overview of this book

Mastering Embedded Linux Programming takes you through the product cycle and gives you an in-depth description of the components and options that are available at each stage. You will begin by learning about toolchains, bootloaders, the Linux kernel, and how to configure a root filesystem to create a basic working device. You will then learn how to use the two most commonly used build systems, Buildroot and Yocto, to speed up and simplify the development process. Building on this solid base, the next section considers how to make best use of raw NAND/NOR flash memory and managed flash eMMC chips, including mechanisms for increasing the lifetime of the devices and to perform reliable in-field updates. Next, you need to consider what techniques are best suited to writing applications for your device. We will then see how functions are split between processes and the usage of POSIX threads, which have a big impact on the responsiveness and performance of the final device The closing sections look at the techniques available to developers for profiling and tracing applications and kernel code using perf and ftrace.
Table of Contents (16 chapters)
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15
Index

Configuring user accounts


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

User names are configured in /etc/passwd. There is one line per user, with seven fields of information separated by colons:

  • 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

  • UID

  • GID

  • A comment field, often left blank

  • The user's home directory

  • (Optional) the shell this user will use

For example, this creates users root with UID 0 and 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 to log on with that name will fail.

Note

Various programs have to read /etc...

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