Debian Package Basics

Introduction

Debian packages are the foundation of software management in Debian-based Linux distributions like Ubuntu, Linux Mint, and Debian itself. They provide a standardized way to distribute and install software, ensuring dependencies are resolved and system integrity is maintained.

In this guide, we'll explore the basics of Debian packages - what they are, how they work, and how to manage them effectively. By the end, you'll have a solid understanding of the Debian packaging system and be able to confidently install, remove, and manage packages on your system.

What is a Debian Package?

A Debian package (with the .deb extension) is an archive file containing:

1. The application or library files
2. Metadata about the package (dependencies, version, description)
3. Installation scripts
4. Configuration files

Think of a Debian package as a "smart" zip file that not only contains the software but also knows how to properly install itself on your system.

Package Naming Convention

Debian packages follow a specific naming convention:

name_version-revision_architecture.deb

For example:

• firefox_109.0-1_amd64.deb
  • firefox is the package name
  • 109.0 is the version
  • 1 is the Debian revision
  • amd64 is the architecture (64-bit x86)

Basic Package Management Tools

APT (Advanced Package Tool)

APT is a high-level package management tool that handles dependencies automatically. It's the recommended way for beginners to manage packages.

Installing Packages with APT

To install a package:

bash

sudo apt install package-name

For example, to install the text editor nano:

bash

sudo apt install nano

Output:

Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following additional packages will be installed:
  [list of dependencies]
Suggested packages:
  [suggested related packages]
The following NEW packages will be installed:
  nano [and dependencies]
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 269 kB of archives.
After this operation, 851 kB of additional disk space will be used.
Do you want to continue? [Y/n] y

Removing Packages with APT

To remove a package while keeping configuration files:

bash

sudo apt remove package-name

To completely remove a package including configuration files:

bash

sudo apt purge package-name

Updating Package Lists

Before installing new packages, it's good practice to update your package lists:

bash

sudo apt update

Upgrading Installed Packages

To upgrade all installed packages to their latest versions:

bash

sudo apt upgrade

DPKG (Debian Package Manager)

DPKG is the low-level tool that actually installs, removes, and provides information about .deb packages. APT uses DPKG behind the scenes.

Installing a Local .deb File

bash

sudo dpkg -i package-file.deb

For example:

bash

sudo dpkg -i google-chrome-stable_current_amd64.deb

Note: Unlike APT, DPKG doesn't automatically resolve dependencies. If dependencies are missing, you'll see errors and need to manually install them or use apt install -f to fix them.

Listing Installed Packages

To list all installed packages:

bash

dpkg -l

Output (excerpt):

| Status | Name | Version | Architecture | Description |
|--------|------|---------|--------------|-------------|
| ii | adduser | 3.118 | all | add and remove users and groups |
| ii | apt | 2.2.4 | amd64 | commandline package manager |

Checking Package Status

To check if a specific package is installed and see its details:

bash

dpkg -s package-name

For example:

bash

dpkg -s bash

Output:

Package: bash
Status: install ok installed
Priority: required
Section: shells
Installed-Size: 6470
Maintainer: Matthias Klose <[email protected]>
Architecture: amd64
Version: 5.1-2+deb11u1
Replaces: bash-doc (<< 2.05-1)
Depends: base-files (>= 2.1.12), debianutils (>= 2.15)
...

Finding Which Package Owns a File

To find out which package a specific file belongs to:

bash

dpkg -S /path/to/file

For example:

bash

dpkg -S /bin/ls

Output:

coreutils: /bin/ls

Package Structure

Let's examine the structure of a Debian package. You can extract a .deb file to see its contents:

bash

mkdir -p extracted/DEBIAN
dpkg-deb --extract package.deb extracted/
dpkg-deb --control package.deb extracted/DEBIAN/

Key Files in a Debian Package

• DEBIAN/control: Contains metadata about the package
• DEBIAN/preinst, postinst, prerm, postrm: Installation and removal scripts
• Other files: The actual application files, organized in the same directory structure they'll have when installed

For example, a simplified control file might look like:

Package: hello
Version: 2.10-2
Architecture: amd64
Maintainer: Santiago Vila <[email protected]>
Installed-Size: 280
Depends: libc6 (>= 2.14)
Section: devel
Priority: optional
Homepage: https://www.gnu.org/software/hello/
Description: example package - GNU hello
 The GNU hello program produces a familiar, friendly greeting.
 It's primarily a demonstration of proper GNU packaging.

Package Repositories

Debian packages are typically obtained from repositories - servers that host collections of packages. The main repository types are:

1. Main: Free software supported by the Debian team
2. Contrib: Free software that depends on non-free software
3. Non-free: Software that isn't free according to Debian's guidelines

Your system's repositories are configured in /etc/apt/sources.list and files in /etc/apt/sources.list.d/.

A typical sources.list entry looks like:

deb http://deb.debian.org/debian bullseye main contrib non-free

Practical Examples

Example 1: Installing a Web Server

Let's install the Apache web server:

bash

sudo apt update
sudo apt install apache2

After installation, Apache starts automatically. You can verify it's running:

bash

systemctl status apache2

You can now visit http://localhost in your browser to see the default Apache page.

Example 2: Managing Package Configuration

When installing packages that need configuration, Debian's package system will often prompt you with configuration questions.

For example, when installing the MySQL server:

bash

sudo apt install mysql-server

You'll be prompted to set a root password and make other configuration choices through a text-based interface.

Example 3: Fixing Broken Dependencies

Sometimes package installations can fail due to dependency issues. To fix them:

bash

sudo apt install -f

This command attempts to correct broken dependencies by installing missing packages.

Example 4: Searching for Packages

To search for packages related to a keyword:

bash

apt search keyword

For example, to find Python packages:

bash

apt search python

Output (excerpt):

Sorting... Done
Full Text Search... Done
bpython/stable 0.21-1 all
  fancy curses interface to the Python interpreter

bpython3/stable 0.21-1 all
  fancy curses interface to the Python3 interpreter

Common Package Management Operations

Here's a quick reference for common package management operations:

Operation	APT Command	DPKG Command
Install package	sudo apt install pkg-name	sudo dpkg -i pkg-file.deb
Remove package	sudo apt remove pkg-name	sudo dpkg -r pkg-name
Purge package	sudo apt purge pkg-name	sudo dpkg -P pkg-name
Update package lists	sudo apt update	N/A
Upgrade packages	sudo apt upgrade	N/A
Search for package	apt search keyword	N/A
List installed packages	apt list --installed	dpkg -l
Show package info	apt show pkg-name	dpkg -s pkg-name
Check which package owns a file	N/A	dpkg -S /path/to/file

Best Practices for Debian Package Management

1. Regular updates: Keep your system updated with sudo apt update && sudo apt upgrade
2. Clean up: Periodically remove unused packages with sudo apt autoremove
3. Check before installing: Use apt show package-name to review what a package does before installing
4. Use official repositories: Stick to official repositories when possible for security
5. Back up configuration: Back up important configuration files before upgrading critical packages

Summary

In this guide, we've covered the basics of Debian packages:

• What Debian packages are and how they're structured
• Using APT for high-level package management
• Using DPKG for low-level package operations
• Understanding package repositories
• Practical examples of package management
• Best practices for maintaining your system

Debian's packaging system is powerful, reliable, and a key reason why Debian-based distributions are popular. Understanding how to effectively manage packages is an essential skill for any Linux user.

Additional Resources

• Debian Package Management Handbook
• Debian Wiki - APT
• Debian New Maintainers' Guide

Exercises

1. Install a text editor of your choice (like vim, emacs, or gedit) using APT.
2. Search for packages related to "game" and install one that interests you.
3. Examine the dependencies of a large package like gnome-desktop.
4. Create a simple bash script to update and upgrade your system, then schedule it to run weekly.
5. Find out which package the /bin/bash file belongs to.