Introduction to apt on Ubuntu

Learn how to install and configure apt on your Ubuntu system

guide

Learn How to Install and Configure apt on Your Ubuntu System

(based on the official Ubuntu Server documentation: https://ubuntu.com/server/docs/package-management)

1. Introduction

apt (Advanced Package Tool) is the standard package manager for Debian‑based distributions, including Ubuntu. It handles package installation, removal, updates, and dependency resolution, and it works with the APT repository system. While apt is pre‑installed on all Ubuntu releases, you may need to configure it for custom repositories, pin priorities, or specific behaviors. This guide walks you through the essentials—installing (if you’re on a minimal system), configuring, and mastering apt on your Ubuntu machine.

Why read this?

  • You’re new to Ubuntu and want a solid foundation in package management.
  • You’re migrating from another system (CentOS, Arch, etc.) and need to know how Ubuntu handles packages.
  • You want to tweak apt for security, performance, or custom packaging workflows.

2. Prerequisites

Requirement Why? How to Verify
Ubuntu (or Ubuntu‑based) apt is tightly integrated with the distro. lsb_release -a or cat /etc/os-release
Root or sudo privileges Most configuration changes require elevated rights. sudo -v
Internet connectivity apt pulls packages from remote repositories. ping -c 3 archive.ubuntu.com
Optional: basic shell knowledge Commands are issued via the terminal. bash or zsh knowledge

3. Understanding the APT System

  1. Repository Metadata – Each repo contains an Index (Packages.gz) that lists available packages and their dependencies.
  2. Configuration Files –
    • /etc/apt/sources.list – main list of repository URLs.
    • /etc/apt/sources.list.d/*.list – additional repo files.
    • /etc/apt/apt.conf.d/ – configuration snippets (e.g., proxy settings).
  3. Package Cache – apt caches package information locally (/var/cache/apt/archives).
  4. APT Commands –
    • apt update – refresh metadata.
    • apt upgrade – apply available updates.
    • apt install pkg – install.
    • apt purge pkg – remove plus config.

4. Basic apt Commands

# 1. Update repository metadata
sudo apt update

# 2. Upgrade all upgradable packages
sudo apt upgrade

# 3. Full upgrade (including package removals)
sudo apt full-upgrade

# 4. Install a package
sudo apt install <package-name>

# 5. Remove a package (keeps config)
sudo apt remove <package-name>

# 6. Purge a package (removes config)
sudo apt purge <package-name>

# 7. Search for a package
apt search <keyword>

# 8. Show package details
apt show <package-name>

Tip: Use apt list --upgradable to view pending upgrades before running apt upgrade.

5. Configuring Repositories

5.1 Editing /etc/apt/sources.list

sudo nano /etc/apt/sources.list

Typical entry format:

deb http://archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse

deb http://security.ubuntu.com/ubuntu focal-security main restricted universe multiverse
deb-src http://security.ubuntu.com/ubuntu focal-security main restricted universe multiverse
  • deb – binary packages.
  • deb-src – source packages.
  • Replace focal with your release codename (lsb_release -cs).

5.2 Adding PPAs (Personal Package Archives)

sudo add-apt-repository ppa:ondrej/php
sudo apt update

Use add-apt-repository (part of software-properties-common).

5.3 Adding Third‑Party Repositories Manually

Create a new .list file:

sudo nano /etc/apt/sources.list.d/custom.repo.list

Add:

deb https://download.docker.com/linux/ubuntu focal stable
deb-src https://download.docker.com/linux/ubuntu focal stable

Then:

sudo apt update

5.4 Proxy Configuration

Create /etc/apt/apt.conf.d/95proxies:

Acquire::http::Proxy "http://proxy.example.com:3128/";
Acquire::https::Proxy "https://proxy.example.com:3128/";

6. Managing Packages

6.1 Pinning Package Versions

Create /etc/apt/preferences.d/custom.pref:

Package: *
Pin: release a=focal
Pin-Priority: 500

Package: nginx
Pin: version 1.18.*
Pin-Priority: 700
  • Packages with a higher priority (e.g., 700) will override lower‑priority sources.
  • A priority of 500 allows installation from the current release but prevents upgrades from newer releases.

Run apt-cache policy <package> to see pinning effects.

6.2 Automating Updates with Unattended Upgrades

sudo apt install unattended-upgrades
sudo dpkg-reconfigure unattended-upgrades

Edit /etc/apt/apt.conf.d/50unattended-upgrades to include:

"${distro_id}:${distro_codename}-security";
"${distro_id}:${distro_codename}-updates";

Enable automatic daily upgrades:

sudo systemctl enable --now unattended-upgrades

6.3 Clean‑Up Commands

# Remove cached packages
sudo apt autoclean

# Remove unused dependencies
sudo apt autoremove

7. Advanced Configuration

Feature Use‑Case Example
APT hooks Run scripts before/after actions (e.g., run tests before install). /etc/apt/apt.conf.d/90hooks with DPkg::Pre-Invoke
APT pinning Keep old kernel while updating others. Pin linux-image-generic at priority 700
Cache directory Custom cache path for limited /var space. Dir::Cache /mnt/apt-cache/
Timeouts & Retries Avoid hangs on flaky networks. Acquire::Retries 5; Acquire::Timeout 120;

Caveat: Over‑configuring apt can break automated updates. Keep a backup of your configuration.

8. Security & Updates

  1. Keep apt Updated

    sudo apt update && sudo apt install apt

  2. Enable Secure Transport
    Verify that your repo URLs use https. If not, consider switching or adding GPG keys manually.

  3. Verify Packages

    sudo apt-key list

    Import keys if needed: wget -qO - https://packages.microsoft.com/keys/microsoft.asc | sudo apt-key add -.

  4. Audit Installed Packages

    sudo apt list --installed | sort | uniq -c

  5. Configure Automatic Security Updates
    Use unattended-upgrades as shown in section 6.2.

9. Troubleshooting

Symptom Likely Cause Fix
E: Unable to locate package Wrong repo entry or missing apt update Verify /etc/apt/sources.list, run sudo apt update
Failed to fetch ... 404 Not Found Repo URL changed or release outdated Update to correct release codename
The following packages have unmet dependencies Broken pinning or incomplete apt update Check apt-cache policy, adjust preferences
apt-get locks out due to another process Another apt/dpkg process running Wait or sudo killall apt-get after confirming no other installs
GPG signature errors Missing repo key Import the key or disable apt’s signature checking (not recommended)

Command to clear lock files (if you’re sure no apt processes are running):
sudo rm /var/lib/dpkg/lock-frontend /var/lib/dpkg/lock
Then run sudo dpkg --configure -a.

10. Further Reading & Resources

Resource Description Link
Ubuntu Server Guide – Package Management Official in‑depth guide. https://ubuntu.com/server/docs/package-management
Debian APT Manual Classic documentation, still highly relevant. https://manpages.debian.org/stable/apt/apt.8.en.html
apt-get vs apt Understanding the newer apt front‑end. https://wiki.debian.org/Apt
Linux Foundation – Advanced Package Management Free course on apt, dpkg, and YUM. https://linuxacademy.com/course/apt/
Ubuntu Security Guide How to secure your Ubuntu system, including package updates. https://ubuntu.com/security
Stack Overflow – apt questions Community Q&A on apt nuances. https://stackoverflow.com/questions/tagged/apt
GitHub – apt-pinning-scripts Community‑maintained scripts for complex pinning. https://github.com/search?q=apt+pinning
Canonical Blog – Unattended Upgrades Official blog on automating security updates. https://ubuntu.com/blog/unattended-upgrades
Reddit r/Ubuntu Community discussions, tips, and troubleshooting. https://www.reddit.com/r/Ubuntu/

11. Summary

  • apt is pre‑installed on Ubuntu, but fine‑tuning it can save time, reduce vulnerabilities, and keep your system stable.
  • Key tasks: apt update, apt upgrade, manage repos via /etc/apt/sources.list or PPAs, pin packages with /etc/apt/preferences.d, automate updates with unattended-upgrades.
  • Security best practices: keep apt updated, use HTTPS repos, verify GPG keys, enable automatic security updates.

Feel free to customize the above guide to match your environment—whether it’s a small personal server or a multi‑node production cluster. Happy packaging!