Package management with apt

apt is how you install software on Debian-based systems. It handles downloading, dependency resolution, installation, and removal. Understanding it well means you spend less time fighting package conflicts.

apt vs apt-get

apt is the user-friendly command. apt-get is the older, lower-level command. Use apt for interactive use, apt-get in scripts (its output format is more stable).

Common operations:

sudo apt update                  # refresh package lists
sudo apt upgrade                 # upgrade all packages
sudo apt install nginx           # install a package
sudo apt remove nginx            # remove (keep config)
sudo apt purge nginx             # remove including config
sudo apt autoremove              # remove unused dependencies

Always run apt update before apt install. If your package lists are stale, apt will fail to find packages that exist.

Searching for packages

apt search nginx                 # search by name/description
apt show nginx                   # show package details
apt list --installed             # list installed packages
apt list --upgradable            # list packages with updates

Find which package provides a file:

dpkg -S /usr/bin/curl
apt-file search /usr/bin/curl    # requires apt-file package

Repositories

Package sources are in /etc/apt/sources.list and /etc/apt/sources.list.d/.

A typical entry:

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

Components:

• main — officially supported, free software
• restricted — officially supported, non-free drivers
• universe — community-maintained, free software
• multiverse — non-free software

Adding a PPA

Personal Package Archives provide newer or third-party packages:

sudo add-apt-repository ppa:ondrej/php
sudo apt update
sudo apt install php8.1

Remove a PPA:

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

PPAs are third-party. Trust them accordingly.

Adding a GPG key and repository manually

For software that provides their own repo:

curl -fsSL https://example.com/gpg.key | sudo gpg --dearmor -o /etc/apt/trusted.gpg.d/example.gpg
echo "deb https://repo.example.com/apt stable main" | sudo tee /etc/apt/sources.list.d/example.list
sudo apt update

Package holds

Prevent a package from being upgraded:

sudo apt-mark hold nginx

Release the hold:

sudo apt-mark unhold nginx

Check held packages:

apt-mark showhold

Useful when you’ve pinned a specific version and don’t want automatic updates to change it.

Version pinning

Install a specific version:

apt show -a nginx            # show available versions
sudo apt install nginx=1.18.0-0ubuntu1

For more control, create preferences in /etc/apt/preferences.d/:

Package: nginx
Pin: version 1.18*
Pin-Priority: 1001

Priority above 1000 forces downgrades. Below 1000 prevents upgrades.

dpkg: low-level operations

dpkg handles individual .deb files without dependency resolution:

sudo dpkg -i package.deb     # install (may fail on dependencies)
sudo apt install -f           # fix broken dependencies
sudo dpkg -r package          # remove
sudo dpkg -l                  # list installed packages

dpkg -i followed by apt install -f is a common pattern for installing local .deb files with dependencies.

Cleaning up

Remove cached package files:

sudo apt clean                # remove all cached packages
sudo apt autoclean            # remove only outdated cached packages

Remove packages installed as dependencies that are no longer needed:

sudo apt autoremove

Check disk usage of the package cache:

du -sh /var/cache/apt/archives/

Common mistakes

Not running apt update first. Your local package index is stale. apt can’t find packages that the repositories have.

Using apt-get when apt works. For interactive use, apt has better output (progress bars, color). Use apt-get in scripts where output stability matters.

Mixing repositories carelessly. Adding repos for the wrong Ubuntu version causes dependency conflicts. Match the repo to your release.

Forgetting autoremove. Over time, unused dependencies pile up. Run apt autoremove periodically.

Remarks

Package management on Ubuntu is straightforward once you understand the workflow: update lists, search, install, clean up. The apt command handles 95% of what you need. When things get complicated — version conflicts, held packages, third-party repos — dpkg and apt pinning give you finer control. Start with apt and reach for dpkg when you need to go deeper.