APT and DPKG Guide (Debian/Ubuntu)

Introduction

apt and dpkg are core tools for package management on Debian and Ubuntu systems. apt update refreshes the package index from configured repositories, ensuring you have the latest package information. dpkg manages .deb packages, allowing direct installation, removal, querying, or identifying file ownership. This guide covers using apt update and dpkg, with use cases like system updates, manual .deb installation, searching for packages, finding file ownership, adding/removing external repositories, and determining which repository provides a package.

What are APT and DPKG?

  • APT (Advanced Package Tool): A high-level package manager that simplifies installing, updating, searching, and removing software. apt update fetches package lists, while commands like apt install, apt upgrade, or apt search handle package operations.
  • DPKG: A low-level tool for managing .deb packages, used for tasks like installing local .deb files, querying installed packages, removing packages, or identifying file ownership.

Together, they provide robust package management for Debian/Ubuntu systems.

Prerequisites

  • Debian/Ubuntu: Version 20.04+.
  • Root Access: Use sudo for most commands.
  • Internet Access: Required for apt update and repository operations.
  • Tools: apt, dpkg, and gnupg are pre-installed on Debian/Ubuntu.

Verify tools:

apt --version
dpkg --version
gpg --version

Critical Warning: Backup Before Changes

How to Use APT Update and DPKG

1. Update Package Lists with apt update

apt update refreshes the package index from repositories listed in /etc/apt/sources.list and /etc/apt/sources.list.d/. Run this before installing or upgrading packages.

sudo apt update

APT update output showing repository refresh Example output:

Hit:1 http://deb.debian.org/debian bullseye InRelease
Get:2 http://deb.debian.org/debian-security bullseye-security InRelease [48.4 kB]
Fetched 48.4 kB in 1s (45.2 kB/s)
Reading package lists... Done
Building dependency tree... Done
All packages are up to date.

Note: If you see errors (e.g., 404 Not Found), check /etc/apt/sources.list or /etc/apt/sources.list.d/ for invalid URLs.

2. Add an External Repository

To install software not in default repositories (e.g., Docker), add a third-party repository to /etc/apt/sources.list or /etc/apt/sources.list.d/. Often, you need to add a GPG key for security.

Example (add Docker repository):

# Add Docker's GPG key
curl -fsSL https://download.docker.com/linux/debian/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

# Add Docker repository
echo "deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/debian bullseye stable" | sudo tee /etc/apt/sources.list.d/docker.list

# Update package lists
sudo apt update

Verify:

cat /etc/apt/sources.list.d/docker.list

Note: Always verify the GPG key and repository URL to avoid security risks.

3. Remove an External Repository

To remove a repository, delete its entry from /etc/apt/sources.list or its file in /etc/apt/sources.list.d/, and optionally remove the GPG key.

Example (remove Docker repository):

# Remove repository file
sudo rm /etc/apt/sources.list.d/docker.list

# Remove GPG key (optional)
sudo rm /usr/share/keyrings/docker-archive-keyring.gpg

# Update package lists
sudo apt update

Verify:

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

Note: Edit /etc/apt/sources.list with sudo nano if the repository is listed there instead.

4. Determine Which Repository Provides a Package

Use apt-cache policy to find which repository provides a package and its available versions.

apt-cache policy <package-name>

Example (check docker-ce):

apt-cache policy docker-ce

Example output:

docker-ce:
  Installed: (none)
  Candidate: 5:24.0.7-1~debian.11~bullseye
  Version table:
     5:24.0.7-1~debian.11~bullseye 500
        500 https://download.docker.com/linux/debian bullseye/stable amd64 Packages

Note: Run sudo apt update first to ensure the package cache is current.

5. Search for a Package

Use apt search or apt-cache search to find packages by name or description.

  • Using apt search (user-friendly, sorted):

    apt search <keyword>

    Example (search for vim):

    apt search vim

    Example output:

    Sorting... Done
Full Text Search... Done
vim/bullseye 2:8.2.2434-3+deb11u1 amd64
  Vi IMproved - enhanced vi editor
vim-tiny/bullseye 2:8.2.2434-3+deb11u1 amd64
  Vi IMproved - enhanced vi editor (tiny version)

  • Using apt-cache search (detailed, unsorted):

    apt-cache search <keyword>

    Example (search for nginx):

    apt-cache search nginx

    Example output:

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

Note: Run sudo apt update first.

6. Find the Package Owning a File

Use dpkg -S to identify which package installed a file.

dpkg -S <file-path>

Example (find package for /usr/bin/vim):

dpkg -S /usr/bin/vim

Example output:

vim: /usr/bin/vim

Note: If the file isn’t found, it may not belong to a package.

7. Upgrade Installed Packages

Upgrade installed packages to their latest versions:

  • Safe Upgrade (avoids removing packages):
    sudo apt upgrade
  • Full Upgrade (may remove packages):
    sudo apt full-upgrade

Example:

sudo apt update
sudo apt upgrade

8. Install a Package with apt

Install a package from repositories:

sudo apt install <package-name>

Example (install vim):

sudo apt install vim

9. Install a Local .deb File with dpkg

Install a downloaded .deb file:

sudo dpkg -i ./package.deb

Example (install google-chrome-stable_current_amd64.deb):

wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
sudo dpkg -i google-chrome-stable_current_amd64.deb

Note: If dependencies are missing, fix with:

sudo apt install -f

10. Query Installed Packages with dpkg

Check if a package is installed or get details:

dpkg -l | grep <package-name>
dpkg -s <package-name>

Example (check vim):

dpkg -l | grep vim
dpkg -s vim

List files installed by a package:

dpkg -L <package-name>

Example:

dpkg -L vim

11. Remove or Purge Packages with dpkg

  • Remove (keeps configuration files):
    sudo dpkg -r <package-name>
  • Purge (removes configuration files):
    sudo dpkg --purge <package-name>

Example (remove vim):

sudo dpkg -r vim

12. Fix Broken Dependencies

If dpkg or apt reports broken dependencies:

sudo apt install -f

Examples

Example 1: Update and Upgrade System

Update package lists and upgrade packages:

# Update package lists
sudo apt update

# Upgrade packages
sudo apt upgrade

Output:

Reading package lists... Done
Building dependency tree... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

Example 2: Add an External Repository

Add the Docker repository:

# Add GPG key
curl -fsSL https://download.docker.com/linux/debian/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

# Add repository
echo "deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/debian bullseye stable" | sudo tee /etc/apt/sources.list.d/docker.list

# Update package lists
sudo apt update

Output (after apt update):

Get:1 https://download.docker.com/linux/debian bullseye/stable amd64 Packages [24.8 kB]
Fetched 24.8 kB in 1s (30.2 kB/s)
Reading package lists... Done

Example 3: Remove an External Repository

Remove the Docker repository:

# Remove repository file
sudo rm /etc/apt/sources.list.d/docker.list

# Remove GPG key
sudo rm /usr/share/keyrings/docker-archive-keyring.gpg

# Update package lists
sudo apt update

Output:

Reading package lists... Done
Building dependency tree... Done
All packages are up to date.

Example 4: Determine Which Repository Provides a Package

Check the repository for docker-ce:

apt-cache policy docker-ce

Output:

docker-ce:
  Installed: (none)
  Candidate: 5:24.0.7-1~debian.11~bullseye
  Version table:
     5:24.0.7-1~debian.11~bullseye 500
        500 https://download.docker.com/linux/debian bullseye/stable amd64 Packages

Example 5: Search for a Package

Search for a package:

apt search vim

Output:

Sorting... Done
Full Text Search... Done
vim/bullseye 2:8.2.2434-3+deb11u1 amd64
  Vi IMproved - enhanced vi editor
vim-tiny/bullseye 2:8.2.2434-3+deb11u1 amd64
  Vi IMproved - enhanced vi editor (tiny version)

Example 6: Find Which Package Owns a File

Identify the package for a file:

dpkg -S /usr/bin/vim

Output:

vim: /usr/bin/vim

Example 7: Install a Local .deb File

Install a .deb file and fix dependencies:

# Download a .deb file
wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb

# Install with dpkg
sudo dpkg -i google-chrome-stable_current_amd64.deb

# Fix dependencies
sudo apt install -f

Output (if dependencies are missing):

dpkg: dependency problems prevent configuration of google-chrome-stable:
 google-chrome-stable depends on libatk1.0-0 (>= 2.32.0); however:
  Package libatk1.0-0 is not installed.
...
sudo apt install -f
...
Setting up libatk1.0-0 (2.36.0-2) ...
Setting up google-chrome-stable (114.0.5735.198-1) ...

Example 8: Query and Remove a Package

Check and remove a package:

# Check package status
dpkg -l | grep vim
dpkg -s vim

# List package files
dpkg -L vim

# Remove package
sudo dpkg -r vim

Output (query):

ii  vim  2:8.2.2434-3+deb11u1  amd64  Vi IMproved - enhanced vi editor

Example 9: Fix Broken Dependencies

If dpkg -i fails:

sudo dpkg -i package.deb
# Errors about missing dependencies
sudo apt install -f

Variants

Adding and Using an External Repository

Add a repository to install specific software (e.g., Docker):

# Add GPG key
curl -fsSL https://download.docker.com/linux/debian/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

# Add repository
echo "deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/debian bullseye stable" | sudo tee /etc/apt/sources.list.d/docker.list

# Update and install
sudo apt update
sudo apt install docker-ce

Removing an External Repository

Remove a repository and clean up:

# Remove repository file
sudo rm /etc/apt/sources.list.d/docker.list

# Remove GPG key
sudo rm /usr/share/keyrings/docker-archive-keyring.gpg

# Update package lists
sudo apt update

Using dpkg to Reconfigure Packages

Reconfigure a package’s settings:

sudo dpkg-reconfigure <package-name>

Example (reconfigure tzdata):

sudo dpkg-reconfigure tzdata

Command Breakdown

  • apt update: Refreshes package index from repositories.
  • apt search: Searches for packages by name or description.
  • apt-cache search: Detailed package search (unsorted).
  • apt-cache policy: Shows which repository provides a package.
  • apt upgrade/full-upgrade: Upgrades installed packages.
  • apt install: Installs packages or fixes dependencies.
  • dpkg -i: Installs a local .deb file.
  • dpkg -S: Finds the package owning a file.
  • dpkg -r/–purge: Removes or purges packages.
  • dpkg -l/-s/-L: Queries installed packages or their files.
  • apt install -f: Resolves broken dependencies.

Use Cases

  • System Maintenance: Regular apt update && apt upgrade for updates.
  • Custom Software: Add external repositories for software like Docker.
  • Package Discovery: Use apt search or apt-cache policy to find packages and their sources.
  • File Ownership: Use dpkg -S to troubleshoot file origins.
  • Manual Installation: Use dpkg -i for .deb files not in repositories.
  • Debugging: Query packages with dpkg -l or dpkg -s.

Pro Tips

  • Verify Repository Sources: Check GPG keys and URLs for security when adding repositories.
  • Cache Cleaning: Free disk space with sudo apt autoclean and sudo apt autoremove.
  • Dry Run: Use apt upgrade --dry-run to preview changes.
  • Force Options with dpkg: Use dpkg -i --force-depends cautiously for missing dependencies.
  • Backup APT Sources: Save /etc/apt/sources.list and /etc/apt/sources.list.d/ before changes.

Troubleshooting

  • 404 Errors in apt update: Check /etc/apt/sources.list or /etc/apt/sources.list.d/:
    sudo nano /etc/apt/sources.list
ls /etc/apt/sources.list.d/
sudo apt update
  • Package Not Found in apt search: Run sudo apt update and verify repositories.
  • apt-cache policy Shows No Repository: Ensure the package is available in a configured repository.
  • dpkg -S Returns Nothing: The file may not belong to a package.
  • Broken Dependencies: Run sudo apt install -f after dpkg -i.
  • Package Conflicts: Remove conflicting packages with sudo dpkg --purge <package-name>.
  • Permission Issues: Use sudo for apt and dpkg commands.
  • Check Logs: View /var/log/dpkg.log or /var/log/apt/history.log.

Resources

Manage packages efficiently with apt update and dpkg for a robust Debian/Ubuntu system!