yum/dnf (RHEL/CentOS) basics in Linux CLI - Commands & Configuration

Introduction

Installing and managing software on RHEL or CentOS Linux can be tricky without the right tools. Yum and Dnf are package managers that help you easily install, update, and remove software packages from your system.

When you want to install new software like a web server or text editor on your CentOS or RHEL system.

When you need to update all your installed software to the latest versions for security and features.

When you want to remove software you no longer need to free up space.

When you want to check if a specific software package is available or installed.

When you want to clean up cached files to save disk space.

Commands

This command installs the 'nano' text editor without asking for confirmation because of the '-y' flag. We use 'sudo' to run it with admin rights.

Terminal

sudo dnf install nano -y

Expected Output

Last metadata expiration check: 0:00:10 ago on Thu 01 Jun 2023 10:00:00 AM UTC.

Dependencies resolved.

================================================================================

 Package       Arch          Version               Repository               Size

================================================================================

Installing:

 nano          x86_64        5.9-1.el8             baseos                  1.2 M

Transaction Summary

================================================================================

Install  1 Package

Total download size: 1.2 M

Installed size: 3.5 M

Downloading Packages:

nano-5.9-1.el8.x86_64.rpm                          1.2 MB/s | 1.2 MB     00:01    

Running transaction check

Running transaction test

Transaction test succeeded

Running transaction

  Preparing        :                                                        1/1 

  Installing       : nano-5.9-1.el8.x86_64                                   1/1 

  Running scriptlet: nano-5.9-1.el8.x86_64                                   1/1 

  Verifying        : nano-5.9-1.el8.x86_64                                   1/1 

Installed:

  nano.x86_64 0:5.9-1.el8

Complete!

→

-y - Automatically answer yes to prompts

This command updates all installed packages to their latest versions without asking for confirmation.

Terminal

sudo dnf update -y

Expected Output

Last metadata expiration check: 0:00:05 ago on Thu 01 Jun 2023 10:05:00 AM UTC.

Dependencies resolved.

================================================================================

 Package           Arch          Version               Repository          Size

================================================================================

Upgrading:

 bash              x86_64        5.0.17-2.el8          baseos             1.1 M

Transaction Summary

================================================================================

Upgrade  1 Package

Total download size: 1.1 M

Downloading Packages:

bash-5.0.17-2.el8.x86_64.rpm                          1.1 MB/s | 1.1 MB     00:01    

Running transaction check

Running transaction test

Transaction test succeeded

Running transaction

  Preparing        :                                                        1/1 

  Upgrading        : bash-5.0.17-2.el8.x86_64                                   1/1 

  Running scriptlet: bash-5.0.17-2.el8.x86_64                                   1/1 

  Verifying        : bash-5.0.17-2.el8.x86_64                                   1/1 

Upgraded:

  bash.x86_64 0:5.0.17-2.el8

Complete!

→

-y - Automatically confirm all prompts

This command removes the 'nano' package from the system without asking for confirmation.

Terminal

sudo dnf remove nano -y

Expected Output

Last metadata expiration check: 0:00:02 ago on Thu 01 Jun 2023 10:10:00 AM UTC.

Dependencies resolved.

================================================================================

 Package       Arch          Version               Repository               Size

================================================================================

Removing:

 nano          x86_64        5.9-1.el8             installed               3.5 M

Transaction Summary

================================================================================

Remove  1 Package

Running transaction check

Running transaction test

Transaction test succeeded

Running transaction

  Preparing        :                                                        1/1 

  Removing         : nano-5.9-1.el8.x86_64                                   1/1 

  Running scriptlet: nano-5.9-1.el8.x86_64                                   1/1 

  Verifying        : nano-5.9-1.el8.x86_64                                   1/1 

Removed:

  nano.x86_64 0:5.9-1.el8

Complete!

→

-y - Skip confirmation prompt

This command checks if the 'nano' package is installed on the system.

Terminal

dnf list installed nano

Expected Output

Installed Packages

nano.x86_64                        5.9-1.el8                         @baseos

This command cleans all cached files from the package manager to free up disk space.

Terminal

sudo dnf clean all

Expected Output

Cleaning repos: baseos appstream extras

Cleaning up everything

Cache directory: /var/cache/dnf is cleaned.

Key Concept

If you remember nothing else from yum/dnf basics, remember: use 'install' to add software, 'update' to upgrade all, and 'remove' to delete software, always with sudo and '-y' to automate.

Common Mistakes

Running 'dnf install nano' without sudo

You get a permission denied error because installing software needs admin rights.

Always prefix with 'sudo' to run as administrator: 'sudo dnf install nano'

Forgetting the '-y' flag and expecting no prompts

The command pauses and waits for you to type 'y' or 'n', which can block automation.

Add '-y' to automatically confirm prompts: 'sudo dnf install nano -y'

Trying to remove a package that is not installed

The package manager will show an error saying the package is not found.

Check if the package is installed first with 'dnf list installed nano' before removing.

Summary

Use 'sudo dnf install package -y' to install software without prompts.

Use 'sudo dnf update -y' to upgrade all installed packages automatically.

Use 'sudo dnf remove package -y' to uninstall software without confirmation.

Use 'dnf list installed package' to check if a package is installed.

Use 'sudo dnf clean all' to clear cached files and save disk space.

Practice

1. What is the primary purpose of the yum or dnf command on RHEL/CentOS systems?

easy

A. To configure network settings

B. To monitor system hardware performance

C. To edit text files in the terminal

D. To manage software packages by installing, updating, or removing them

Solution

1. Step 1: Understand the role of yum/dnf

   yum and dnf are package managers used to handle software packages on RHEL/CentOS.

2. Step 2: Identify the correct function

   They allow users to install, update, and remove software easily.

3. Final Answer:

   To manage software packages by installing, updating, or removing them -> Option D

4. Quick Check:

   yum/dnf = software package management [OK]

Hint: yum/dnf commands control software packages [OK]

Common Mistakes:

• Confusing yum/dnf with system monitoring tools
• Thinking yum/dnf edits files or network settings
• Mixing yum/dnf with text editors

2. Which of the following is the correct syntax to install a package named httpd using dnf with automatic yes to prompts?

easy

A. dnf install httpd y

B. dnf -y install httpd

C. dnf -y httpd install

D. dnf httpd install -y

Solution

1. Step 1: Understand dnf command syntax

   The -y option should come immediately after dnf to apply to the entire command.

2. Step 2: Check the order of arguments

   Correct syntax is dnf -y install httpd to install with automatic yes.

3. Final Answer:

   dnf -y install httpd -> Option B

4. Quick Check:

   dnf -y install package = correct syntax [OK]

Hint: Place -y right after dnf for automatic yes [OK]

Common Mistakes:

• Putting -y after the package name
• Mixing argument order causing syntax errors
• Using incorrect command order

3. What will be the output of the command dnf list installed | grep bash on a system where bash is installed?

medium

A. A list of all packages except bash

B. An error saying 'bash not found'

C. A list line showing the bash package details

D. No output at all

Solution

1. Step 1: Understand the command components

   dnf list installed lists all installed packages; piping to grep bash filters lines containing 'bash'.

2. Step 2: Predict output if bash is installed

   Since bash is installed, the output will show the bash package line.

3. Final Answer:

   A list line showing the bash package details -> Option C

4. Quick Check:

   dnf list installed | grep bash = bash package line [OK]

Hint: grep filters output lines containing the keyword [OK]

Common Mistakes:

• Expecting an error if package exists
• Thinking grep excludes matching lines
• Assuming no output means package installed

4. You run sudo yum install -y nginx but get an error: Could not find a valid baseurl for repo. What is the most likely cause?

medium

A. Network connection or repository configuration issue

B. The nginx package does not exist

C. You forgot to use sudo

D. The command syntax is incorrect

Solution

1. Step 1: Analyze the error message

   The error 'Could not find a valid baseurl for repo' means yum/dnf cannot reach the repository URL.

2. Step 2: Identify common causes

   This usually happens due to network issues or wrong repo configuration, not package absence or syntax errors.

3. Final Answer:

   Network connection or repository configuration issue -> Option A

4. Quick Check:

   Repo baseurl error = network or repo config problem [OK]

Hint: Check network and repo config if baseurl error appears [OK]

Common Mistakes:

• Assuming package missing causes baseurl error
• Ignoring need for network access
• Blaming command syntax for repo errors

5. You want to automate updating all packages on a CentOS system without prompts. Which command should you use?

hard

A. sudo dnf update -y

B. sudo yum update

C. sudo dnf install -y

D. sudo yum remove -y

Solution

1. Step 1: Identify the command to update all packages

   dnf update or yum update updates all installed packages.

2. Step 2: Add automation to avoid prompts

   Adding -y automatically answers yes to prompts, enabling automation.

3. Final Answer:

   sudo dnf update -y -> Option A

4. Quick Check:

   dnf update -y = automated full update [OK]

Hint: Use -y with update to automate package upgrades [OK]

Common Mistakes:

• Using install instead of update to upgrade packages
• Forgetting sudo for permission
• Using remove instead of update