Lesson 2: The Librarian (Advanced Package Management)

You've learned how to install software with apt. But a true DevOps engineer needs to search, inspect, and manage packages like a librarian managing a massive library.

Searching the Catalog: apt-cache search

Don't know the exact package name? Search for it:

apt-cache search web server

This searches through all available packages and returns matches. You'll see results like:

nginx - small, powerful, scalable web/reverse proxy server
apache2 - Apache HTTP Server

Inspecting a Package: apt-cache show

Before installing, check what a package does, its version, dependencies, and size:

apt-cache show nginx

This shows:

• Version — Which version is available.
• Depends — What other packages it needs.
• Size — How big the download is.
• Description — What the software actually does.

Listing Installed Packages: dpkg

dpkg is the lower-level package manager behind apt. To see what's already installed:

dpkg -l               # List ALL installed packages
dpkg -l | grep nginx  # Search for a specific one

Removing Packages

apt remove nginx          # Remove but keep config files
apt purge nginx           # Remove everything, including configs
apt autoremove            # Clean up unused dependencies

Mission Objective

You're auditing a server to understand what's installed:

1. Search the catalog: Run apt-cache search nginx to find web server packages.
2. Read the details: Use apt-cache show curl to inspect the curl package.
3. Audit the system: Run dpkg -l | head -20 to see the first 20 installed packages.

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Pro Tip

Always run apt update before apt install to make sure you're getting the latest version. Stale package lists are a common source of "package not found" errors.