102.4 Use Debian package management

Introduction

This lesson is about Debian-style package management.

The main question is:

How do you install, remove, inspect, and search packages on Debian-based systems?

What you should be able to do after this lesson:

• Use dpkg for local package operations.
• Use apt-get and apt-cache for repository-based work.
• Find which package owns a file.
• Read package status and dependency information.
• Recognize /etc/apt/sources.list.

Two Layers: dpkg and apt

dpkg

This is the low-level Debian package tool. It works directly with .deb packages.

apt

This is the higher-level tool that works with repositories and dependency resolution.

Simple way to remember it:

dpkg works on package files; apt works on package sources and dependencies

Basic dpkg Commands

Install a local package

sudo dpkg -i package.deb

Important beginner note:

• dpkg -i works directly on a local package file
• if dependencies are missing, the package may not end up fully configured until you fix them

Remove a package but keep config files

sudo dpkg -r package-name

Remove a package and its config files

sudo dpkg -P package-name

Show package status

dpkg -s package-name

Show installation status in a package list

dpkg -l | head

List installed files from a package

dpkg -L package-name

Find which package owns a file

dpkg -S /usr/bin/ssh

Representative example output:

openssh-client: /usr/bin/ssh

What this shows:

• the package name is on the left
• the owned file path is on the right

Basic apt-get Commands

Update package lists

sudo apt-get update

Install a package

sudo apt-get install package-name

Upgrade packages

sudo apt-get upgrade

Remove a package

sudo apt-get remove package-name

apt-cache: Search and Inspect

Search by keyword

apt-cache search nginx

Representative example output:

nginx - small, powerful, scalable web/proxy server
nginx-common - small, powerful, scalable web/proxy server - common files

What this shows:

• apt-cache search returns matching package names and short descriptions
• one search term can return multiple related packages

Show package information

apt-cache show nginx

Check version and repository info

apt-cache policy nginx

Show dependencies

apt-cache depends nginx

Package Sources

Repository definitions often live in:

/etc/apt/sources.list
/etc/apt/sources.list.d/

The exam idea is simple:

• these files tell APT where packages come from

dpkg-reconfigure

This tool lets you re-run package configuration questions for some packages.

Example:

sudo dpkg-reconfigure tzdata

Reinstall and Package Integrity Awareness

LPIC expects more than just install/remove basics.

Useful ideas to recognize:

• a package can be installed but misconfigured
• a file can exist even when the package is not currently installed
• dependency information matters when troubleshooting broken package states

Common reinstall pattern:

sudo apt-get install --reinstall package-name

Common package questions:

• Is it installed?
• What version is it?
• What files does it contain?
• What does it depend on?

A Safe Mental Workflow

When using Debian package tools:

1. apt-get update
2. inspect package info if needed
3. install or upgrade
4. use dpkg when you need package-file details

Practice Step by Step

1) Find which package owns a file

1. Run: dpkg -S /usr/bin/ssh
2. Read the package name on the left.

2) Search for a package before installing it

1. Update metadata: sudo apt-get update
2. Search: apt-cache search editor
3. Inspect a candidate: apt-cache show nano

3) Reconfigure an installed package

1. Run: sudo dpkg-reconfigure tzdata
2. Follow the prompts.

Cheat Sheet

• dpkg -i = install a local .deb
• dpkg -r = remove package, keep configs
• dpkg -P = purge package and configs
• dpkg -s = show package status
• dpkg -L = list files from a package
• dpkg -S <file> = find package owning a file
• apt-get update = refresh package lists
• apt-get install = install from repos
• apt-get upgrade = upgrade packages
• apt-cache search = search packages
• apt-cache show = show package details
• /etc/apt/sources.list = package source configuration