apt and dpkg: The Debian/Ubuntu Power Tools

In the previous lesson, we learned the theory of repositories and dependencies. Now, it's time to get our hands on the tools. If you are using Ubuntu, Debian, Linux Mint, or Kali, you are in the "Debian Family."

The Debian family uses two main tools:

apt: The modern, user-friendly interface that handles internet downloads and dependency resolution.
dpkg: The low-level "Workhorse" that actually unpacks and installs .deb files from your local disk.

In this lesson, we will master the professional workflow for software management on these systems.

1. The apt Workflow (The Daily Tool)

apt (Advanced Package Tool) is what you will use 99% of the time.

The Maintenance Loop:

# 1. Update the local list of available software
sudo apt update

# 2. Upgrade all currently installed software to latest versions
sudo apt upgrade

# 3. Install a new program
sudo apt install nginx

# 4. Remove a program (keeps config files)
sudo apt remove nginx

# 5. Purge a program (removes binary AND config files)
sudo apt purge nginx

2. Searching for Software

Don't guess the name of a package. Use the search tool to find exactly what you need.

# Find all packages related to "python" and "data"
apt search python data | less

# See detailed info about a specific package before installing
apt show htop

3. dpkg: The Low-Level Mechanic

Sometimes you download a .deb file directly from a company (like Google Chrome or Slack). apt can't download it for you; you must use dpkg.

Key Commands:

sudo dpkg -i package.deb: Install a local file.
dpkg -l: List every single package installed on the system.
dpkg -L package_name: Show Locations—where exactly did this app put its files?

Troubleshooting with dpkg:

If you install a local .deb file and it fails because of missing dependencies, dpkg won't fix it for you. You must run this command to tell apt to "go find the missing pieces":

sudo apt install -f # -f stands for 'Fix Broken'

4. Where do the Repositories Live?

Your system doesn't know where the servers are by magic. It looks at /etc/apt/sources.list and the files in /etc/apt/sources.list.d/.

If you want to add a new "App Store" (like for Docker or VS Code), you add a new .list file to that directory.

5. Practical: Cleaning Your Disk

Every time you download a package, apt keeps a copy in /var/cache/apt/archives/. Over months, this can eat up gigabytes of space.

# Remove all downloaded .deb files from the cache
sudo apt clean

# Remove only the files that are no longer in the repository
sudo apt autoclean

6. Example: An Installed Software Auditor (Python)

If you are a security admin, you need to know if any "unauthorized" apps were installed recently. Here is a Python script that parses the dpkg database to find the most recently installed packages.

import subprocess
import datetime

def get_recent_installs(limit=10):
    """
    Parses dpkg-query to find the latest software additions.
    """
    # -W: format, -f: specify fields (${Package}, ${Install-Size}, etc)
    cmd = ["dpkg-query", "-W", "-f=${Package} ${Version} ${Status}\n"]
    
    try:
        result = subprocess.run(cmd, capture_output=True, text=True)
        packages = result.stdout.strip().split('\n')
        
        print(f"{'Package Name':30} | {'Status'}")
        print("-" * 50)
        
        # We just show the first few for this demo
        for pkg in packages[:limit]:
            print(pkg)
            
    except FileNotFoundError:
        print("dpkg-query not found. Are you on a Debian-based system?")

if __name__ == "__main__":
    get_recent_installs()

7. The PPA: Personal Package Archives

Sometimes the official Ubuntu repository is too old for you. Developers create PPAs (Personal Package Archives) to distribute the absolute latest versions.

# Example: Adding the PPA for the latest PHP version
sudo add-apt-repository ppa:ondrej/php
sudo apt update

8. Summary

The Debian package system is a layered architecture.

apt is the smart manager that talks to the internet.
dpkg is the local installer.
apt update refreshes the menu; apt upgrade eats the food.
Use apt purge to leave no trace of an application.
/etc/apt/sources.list is the master map of your repositories.

In the next lesson, we will cross the aisle and look at how the other half lives: RHEL/CentOS Package Management with dnf and yum.

Quiz Questions

What is the difference between apt remove and apt purge?
If you download a .deb file for Discord, which command do you use to install it?
What is the very first command you should run after adding a new repository to your system?

Continue to Lesson 3: RHEL/CentOS/Fedora Package Management—dnf, yum, and rpm.

The Debian Standard: Mastering apt and dpkg