RedHat/DNF

Objectives

• Understand the RPM format and ecosystem.
• Master dnf for enterprise-grade package management.
• Learn about Yum repositories and AppStreams.

1. Low-Level Management: rpm

The rpm (Red Hat Package Manager) tool is the low-level foundation for handling .rpm files, directly analogous to dpkg in the Debian world. It interacts with the local RPM database and individual package files.

The Key Limitation: No Dependency Resolution

Like dpkg, rpm cannot resolve dependencies automatically. If you attempt to install an RPM that requires other packages, the installation will fail, leaving you to manually find and install the requirements.

Core Commands

Understanding the Flags

• -i (Install): Installs a new package.
• -v (Verbose): Provides detailed output during the process.
• -h (Hash): Prints hash marks (#) to show installation progress.
• -e (Erase): Removes a package from the system.
• -q (Query): Asks the RPM database for information.
• -a (All): When used with -q, searches all installed packages.
• -f (File): When used with -q, searches for the package that owns a specific file.
• -V (Verify): Compares the current state of files against the original metadata (MD5, size, permissions).

2. High-Level Management: dnf

dnf (Dandified Yum) is the modern, primary tool for managing software on Red Hat-based systems (Fedora, RHEL, CentOS Stream, AlmaLinux, Rocky Linux). It succeeded yum and is built for better performance and dependency resolution.

Key Difference from APT

Unlike apt, dnf automatically refreshes its repository metadata before performing operations. This means you generally do not need to run a separate "update" command (like apt update) before installing new software.

Dnf Core Commands

Enterprise Power Feature: dnf history

One of DNF's most powerful features for system administrators is the ability to track and undo transactions.

• dnf history: Lists all recent package transactions with IDs.
• dnf history info <id>: Shows exactly what happened in a specific transaction (which packages were added/removed).
• sudo dnf history undo <id>: Roll back the changes made in a specific transaction. This is essential for recovering from a problematic update.

Modularity and AppStreams

RHEL-family systems use AppStreams to provide multiple versions of the same software stack (e.g., Python 3.8 vs. 3.9 or Node.js 14 vs. 16) on the same OS release.

• dnf module list: Shows available software modules and their versions (streams).
• sudo dnf module install nodejs:16: Installs a specific version of a module.

3. Repository Configuration

Repository information is stored in files ending in .repo within the /etc/yum.repos.d/ directory.

Anatomy of a .repo File

[baseos]
name=Red Hat Enterprise Linux $releasever - BaseOS
baseurl=http://mirror.example.com/rhel/$releasever/BaseOS/$basearch/os/
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release

• [baseos]: A unique ID for the repository.
• name: A human-readable name for the repository.
• baseurl: The URL where the package files are hosted.
• enabled=1: Tells DNF to use this repository (set to 0 to disable).
• gpgcheck=1: Ensures DNF verifies the GPG signature of packages before installation.

Essential Repositories: EPEL

For RHEL, AlmaLinux, or Rocky Linux, the EPEL (Extra Packages for Enterprise Linux) repository is almost always required. It provides high-quality, community-maintained packages that are not included in the standard RHEL repositories (e.g., htop, nginx, certbot).

4. Practical Comparison: APT vs. DNF

Resources

• DNF Documentation