Book Image

Red Hat Enterprise Linux 9 Administration - Second Edition

By : Pablo Iranzo Gómez, Pedro Ibáñez Requena, Miguel Pérez Colino, Scott McCarty
2 (2)
Book Image

Red Hat Enterprise Linux 9 Administration - Second Edition

2 (2)
By: Pablo Iranzo Gómez, Pedro Ibáñez Requena, Miguel Pérez Colino, Scott McCarty

Overview of this book

With Red Hat Enterprise Linux 9 becoming the standard for enterprise Linux used from data centers to the cloud, Linux administration skills are in high demand. With this book, you’ll learn how to deploy, access, tweak, and improve enterprise services on any system on any cloud running Red Hat Enterprise Linux 9. Throughout the book, you’ll get to grips with essential tasks such as configuring and maintaining systems, including software installation, updates, and core services. You’ll also understand how to configure the local storage using partitions and logical volumes, as well as assign and deduplicate storage. You’ll learn how to deploy systems while also making them secure and reliable. This book provides a base for users who plan to become full-time Linux system administrators by presenting key command-line concepts and enterprise-level tools, along with essential tools for handling files, directories, command-line environments, and documentation for creating simple shell scripts or running commands. With the help of command line examples and practical tips, you’ll learn by doing and save yourself a lot of time. By the end of the book, you’ll have gained the confidence to manage the filesystem, users, storage, network connectivity, security, and software in RHEL 9 systems on any footprint.
Table of Contents (26 chapters)
1
Part 1 – Systems Administration – Software, User, Network, and Services Management
9
Part 2 – Security with SSH, SELinux, a Firewall, and System Permissions
14
Part 3 – Resource Administration – Storage, Boot Process, Tuning, and Containers
21
Part 4 – Practical Exercises

Adjusting password policies

As was mentioned in Chapter 3, Basic Commands and Simple Shell Scripts, users are stored in the /etc/passwd file while the encrypted passwords, or password hashes, are stored in the /etc/shadow file.

Tip

A hashing algorithm is made so that it generates a precise string of characters, or a hash, from a provided piece of data (that is, a file or a word). It does it in a way that it will always generate the same hash from the same original data, but the original data is almost impossible to recreate from the hash. That’s why they are used to store passwords or verify the integrity of a downloaded file.

Let’s take a look at one example by running the grep user as root against /etc/shadow:

user:$6$tOT/cvZ4PWRcl8XX$0v3.ADE/ibzlUGbDLer0ZYaMPNRJ5gK17LeKno MfKK9 .nFz8grN3IafmHvoHPuh3XrU81nJu0.is5znztB64Y/:18650:0:99999 :7:3:19113:

As with the password file, the data stored in /etc/shadow has an entry per line and the fields are separated...