Linux Package Management | apt, dnf & Repos

You will install, query, pin, and add repositories for software using apt on Debian/Ubuntu and dnf on RHEL/Fedora. By the end you can keep servers patched, audit what is installed, and add third-party repos safely.

Learning Objectives

Install, remove, and search packages on both package managers.
Add a third-party repository with a verified signing key.
Pin a package version and audit installed software.
Time: ~2 hours · Difficulty: Beginner · Prereqs: a Debian-family and/or RHEL-family server.

Architecture Overview

Environment Setup

You will need: a server with apt or dnf and internet access.

Before you begin: know which family you are on (cat /etc/os-release).

Step-by-Step Execution

Install and search (Debian family)

apt resolves dependencies automatically; searching helps find the right package name.

sudo apt update && apt search nginx && sudo apt install -y nginx

[ROOT REQUIRED] Updates metadata and installs nginx.

Equivalent on RHEL family

sudo dnf install -y nginx && dnf info nginx

Add a third-party repo with a verified key

Verifying the signing key is what makes adding an external repo safe rather than risky.

curl -fsSL https://example.com/key.gpg | sudo gpg --dearmor -o /usr/share/keyrings/example.gpg

Audit what is installed

$ apt list --installed 2>/dev/null | wc -l

734

$ # review with: apt list --installed | grep -i nginx

Progress So Far

graph LR A[01 Install/search] -->|done| B[02 Cross-distro] B -->|done| C[03 Add repo + key] C -->|done| D[04 Audit] style A fill:#1a4a1a,stroke:#00ff00,color:#fff style B fill:#1a4a1a,stroke:#00ff00,color:#fff style C fill:#1a4a1a,stroke:#00ff00,color:#fff style D fill:#1a4a1a,stroke:#00ff00,color:#fff

Testing & Validation

nginx -v && systemctl is-enabled nginx

You should see the installed version and that the service is enabled. If so, package management is working end to end.

Troubleshooting

NO_PUBKEY error: import the repo's signing key into a keyring before updating.
Held/broken packages: run sudo apt --fix-broken install.
Wrong version installed: pin with apt preferences or dnf versionlock.

Extension Ideas

Automate patching with unattended-upgrades.
Build a local mirror or caching proxy (apt-cacher-ng) for many hosts.
Compare native packages with Snap/Flatpak trade-offs.

Key Results

Installed and verified software on both apt and dnf systems.
Added a third-party repo with a verified GPG key, no insecure trust.
Audited 700+ installed packages for review.
Established version pinning to prevent unwanted upgrades.

Linux Package Management with apt and dnf