102.4 Use Debian package management¶

Concept of the package management system¶

GNU/Linux distributions maintain large archives of pre-compiled software called repositories, managed by package manager tools that handle searching, installing, resolving dependencies, resolving conflicts, and updating. Debian-based distros use .deb files as their packages and tools like dpkg, apt-get, apt-cache, and apt to manage them.

Debian packages are named like NAME-VERSION-RELEASE_ARCHITECTURE.deb, for example tmux_3.2a-4build1_amd64.deb.

Package management layers:

  apt-get / apt-cache / apt       (high-level: repositories, dependencies, updates)
        |
        v
  dpkg                            (low-level: install/remove individual .deb files)
        |
        v
  .deb files on disk

dpkg works on individual .deb files but cannot resolve dependencies. apt-get/apt works with repositories and handles dependencies automatically. Think of dpkg as the engine and apt as the driver.

apt vs apt-get¶

apt is a newer, "friendlier" command that combines the most used options of apt-get and apt-cache into one tool. Most commands are interchangeable:

Task	apt-get / apt-cache	apt
Update package list	`apt-get update`	`apt update`
Install a package	`apt-get install tmux`	`apt install tmux`
Remove a package	`apt-get remove tmux`	`apt remove tmux`
Upgrade all packages	`apt-get upgrade`	`apt upgrade`
Search for a package	`apt-cache search tmux`	`apt search tmux`
Show package info	`apt-cache show tmux`	`apt show tmux`
Fix broken packages	`apt-get install -f`	`apt install -f`

Why learn apt-get if apt exists? The PDF states: since apt may not be installed on every system, it is recommended to learn apt-get and apt-cache. On minimal or older systems, apt-get is guaranteed to be there; apt might not be. Also, apt-get is more stable for use in scripts, while apt adds features like a progress bar that are designed for interactive (human) use.

Repositories¶

Repositories are where packages come from - a network server, local disk, or even a DVD. The configuration lives at:

/etc/apt/sources.list - the main sources file
/etc/apt/sources.list.d/ - additional .list files (one per extra repo)

A typical sources.list line:

deb http://us.archive.ubuntu.com/ubuntu/ jammy main restricted universe multiverse

The format is: archive-type URL distribution component(s)

Field	Meaning
`deb` or `deb-src`	Binary packages or source code
URL	Repository address
Distribution	Release codename (e.g. `jammy` for Ubuntu 22.04)
Components	`main` (official open-source), `restricted` (official closed-source), `universe` (community open-source), `multiverse` (unsupported/patent-encumbered)

Updating repository information (does NOT upgrade any software, just refreshes the list of what's available):

apt-get update

Installing packages¶

apt-get install tmux                  # install a package (resolves dependencies automatically)
apt-get install -s tmux               # dry-run/simulation only, shows what would happen
apt-get install --download-only tmux  # download .deb files to cache without installing
apt-get download tmux                 # download the .deb to current directory

Downloaded packages are cached in /var/cache/apt/archives/.

Removing debian packages¶

apt-get remove tmux            # remove the package, keep config files
apt-get autoremove tmux        # remove the package AND its unused dependencies
apt-get autoremove             # remove any dependencies no longer needed by anything

Notes: - remove alone does NOT remove dependencies that were pulled in automatically - If you remove a package that other packages depend on, apt will warn you and list what else will be removed

Note on "removing 100%": dpkg -P tmux (purge) removes tmux and its config files, but leaves its dependencies behind. apt autoremove tmux removes tmux and its unused dependencies, but leaves the config files behind. Neither one alone does both jobs.

sudo apt autoremove --purge tmux    # one command: configs gone, unused deps gone

This one line does both. But it only checks tmux's own dependencies at that moment. For a full clean-up (including old leftovers from other past removals), two separate commands work better:

sudo apt purge tmux        # remove tmux + its config files
sudo apt autoremove        # clean up ANY unused dependency on the whole system

Searching for packages¶

apt-cache search "tiny window"     # search package names and descriptions
apt search grub2                   # same thing using the newer apt command

Upgrading¶

apt-get install tzdata       # upgrade a single package (install and upgrade use the same command)
apt-get upgrade              # upgrade all installed packages to latest versions
apt-get dist-upgrade         # upgrade to a new distribution release (may add/remove packages)

The default apt configuration is at /etc/apt/apt.conf, manageable via apt-config.

Reconfiguring packages¶

Debian packages can run configuration actions after installation (via debconf). To re-run that configuration on an already installed package:

dpkg-reconfigure tzdata      # re-asks the timezone questions as if you just installed it

Useful when a config file is corrupted or you want to change answers you gave during initial setup.

Package information with dpkg¶

dpkg is the low-level tool for working directly with .deb files. Format: dpkg [OPTIONS] ACTION PACKAGE

Switch	Long form	Description
`-c`	`--contents`	Show the contents of a `.deb` file (what files it would install)
`-C`	`--audit`	Search for broken installed packages and propose solutions
	`--configure`	Reconfigure an installed package
`-i`	`--install`	Install or upgrade a `.deb` file. Does NOT resolve dependencies
`-I`	`--info`	Show detailed info about a `.deb` file (version, dependencies, description)
`-l`	`--list`	List all installed packages matching a pattern
`-L`	`--listfiles`	List all files installed by a specific package
`-P`	`--purge`	Remove the package AND its configuration files (stronger than `-r`)
`-r`	`--remove`	Remove the package but keep its configuration files
`-s`	`--status`	Display the current status of an installed package
`-S`	`--search`	Find which installed package owns a given file

Examples:

dpkg --contents tmux_3.2a-4build1_amd64.deb   # peek inside a .deb without installing
dpkg -i tmux_3.2a-4build1_amd64.deb           # install from a local .deb file
dpkg -s tmux                                   # is tmux installed? what version?
dpkg -L tmux                                   # what files did tmux install?
dpkg -S /usr/bin/tmux                          # which package owns /usr/bin/tmux?
dpkg -P tmux                                   # remove tmux AND its config files

Key difference: -r vs -P - -r (remove): deletes the program but leaves config files behind. If you reinstall later, your old settings are still there - -P (purge): deletes everything, program and configs. Clean slate

Key difference: -i vs apt-get install - dpkg -i installs one .deb file, does NOT resolve dependencies (fails if they're missing) - apt-get install fetches from repositories AND resolves all dependencies automatically

If a dpkg -i leaves broken dependencies, fix them with:

apt-get install -f     # -f = fix broken

Common apt-get options¶

Command	Usage
`autoclean`	Remove cached `.deb` files for packages that are no longer available
`check`	Check the package database for consistency issues
`clean`	Delete all cached `.deb` files from `/var/cache/apt/archives/` to free disk space
`dist-upgrade`	Major upgrade - can add/remove packages to satisfy new dependencies
`install`	Install or upgrade packages
`remove`	Remove a package (keep configs)
`source`	Download the source code of a package
`update`	Refresh the package list from repositories (NOT upgrade software)
`upgrade`	Upgrade all installed packages to latest versions (won't remove anything)

Common apt-cache options¶

Command	Usage
`depends`	Show what a package depends on
`pkgnames`	List all known package names
`search`	Search package names and descriptions
`showpkg`	Show detailed info about a package
`stats`	Show repository statistics
`unmet`	Show unmet dependencies

Other tools¶

Other tools include aptitude (text-based interactive package manager) and graphical tools used in KDE and GNOME desktop environments.

Summary¶

I have a Debian-based Linux system where software is distributed as .deb packages. There are two layers of tools: dpkg at the bottom works directly with individual .deb files (install with -i, remove with -r, purge with -P, query with -s/-S/-L), but it cannot resolve dependencies on its own. Above it, apt-get and apt-cache work with online repositories defined in /etc/apt/sources.list, automatically downloading packages and their dependencies.

The workflow I'll use most often is apt-get update to refresh the package list, then apt-get install to install, apt-get upgrade to upgrade all packages, and apt-get remove or autoremove to clean up. If a package has post-install configuration prompts I need to change later, dpkg-reconfigure re-runs them. If a dpkg -i leaves a package in a broken state with missing dependencies, apt-get install -f fixes it.

The one naming trap to watch for is update vs upgrade: apt-get update only refreshes the list of available packages (like checking what's new at the store), while apt-get upgrade actually installs the newer versions (like buying and bringing them home). Running upgrade without update first means you're upgrading based on stale information.