CentOS Stream 9 Essentials is designed to provide detailed information on the installation, use, and administration of the CentOS 9 distribution. For beginners, the book covers topics such as operating system installation, the basics of the GNOME desktop environment, configuring email and web servers, and installing packages and system updates using App Streams. Additional installation topics, such as dual booting with Microsoft Windows, are also covered, together with all important security topics, such as configuring a firewall and user and group administration.
For the experienced user, topics such as remote desktop access, the Cockpit web interface, logical volume management (LVM), disk partitioning, swap management, KVM virtualization, Secure Shell (SSH), Linux Containers, and file sharing using both Samba and NFS are covered in detail to provide a thorough overview of this enterprise class operating system.
CentOS Stream 9, in common with Linux in general, has two types of user accounts, one being a standard user account with restricted access to many of the administrative files and features of the operating system and the other a superuser (root) account with elevated privileges. Typically, a user can gain root access either by logging in as the root user or using the su – command and entering the root password. In the following example, a user is gaining root access via the su – command:
[demo@demo-server ~]$ su Password: [demo@demo-server ~]#Code language: plaintext (plaintext)
Note that the command prompt for a regular user ends with a $ sign while the root user has a # character. When working with the command line, this is a useful indication of whether you are currently issuing commands as the root user.
If the su – command fails, the root account on the system has most likely been disabled for security reasons. In this case, the sudo command can be used instead, as outlined below.
Using sudo, a single command requiring root privileges may be executed by a non-root user. Consider the following attempt to update the operating system with the latest patches and packages:
[neil@demo-server ~]$ dnf updateCode language: plaintext (plaintext)
Not root, Subscription Management repositories not updated Error: This command has to be run under the root user.
Optionally, user accounts may be configured so that they have access to root-level privileges. Instead of using the su – command to first gain root access, user accounts with administrative privileges can run otherwise restricted commands using sudo:
[demo@demo-server]$ sudo dnf update We trust you have received the usual lecture from the local System Administrator. It usually boils down to these three things: #1) Respect the privacy of others. #2) Think before you type. #3) With great power comes great responsibility. [sudo] password for demo: . .Code language: plaintext (plaintext)
To perform multiple commands without repeatedly using the sudo command, a command prompt with persistent super-user privileges may be accessed as follows:
[demo@demo-server]$ sudo su - [demo@demo-server]#Code language: plaintext (plaintext)
The reason for raising this issue so early in the book is that many of the command-line examples outlined in this book will require root privileges. Rather than repetitively preface every command-line example with directions to run the command as root, the command prompt at the start of the line will be used to indicate whether the command needs to be performed as root. If the command can be run as a regular user, the command will be prefixed with a $ command prompt as follows:
$ dateCode language: plaintext (plaintext)
If, on the other hand, the command requires root privileges, the command will be preceded by a # command prompt:
# dnf install opensshCode language: plaintext (plaintext)
Opening a Terminal Window
If you are using the GNOME desktop and need to access a command prompt, you must open a Terminal window. To do this, either press the keyboard Windows key or click on the Activities button in the top left-hand corner of the screen, then select the Terminal from the dash as shown in Figure 1-1:
Configuring a Linux system typically involves editing files. For those new to Linux, it can be unclear which editor to use. If you are running a terminal session and do not already have a preferred editor, we recommend using the nano editor. To launch nano in a terminal window, simply enter the following command:
# nano <file>Code language: plaintext (plaintext)
Where <file> is replaced by the path to the file you wish to edit. For example:
# nano /etc/passwdCode language: PHP (php)
Once loaded, nano will appear as illustrated in Figure 1-2:
To create a new file, simply run nano as follows:
# nanoCode language: plaintext (plaintext)
After editing the file, type Ctrl-S to save the file, followed by Ctrl-X to exit. To open an existing file, use the Ctrl-R keyboard shortcut.
If you prefer to use a graphical editor within the GNOME desktop environment, gedit is a useful starting point for basic editing tasks. To launch gedit from the desktop, press Alt-F2 to display the Enter a Command window as shown in Figure 1-3:
Enter gedit into the text field and press the Enter key. After a short delay, gedit will load ready to open, create, and edit files:
Alternatively, launch gedit from a terminal window either with or without the path to the file to open:
# gedit # gedit /etc/passwdCode language: plaintext (plaintext)
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