LPIC-1 102.4 — Use Debian Package Management

Exam weight: 3 — LPIC-1 v5, Exam 101

What you need to know

• Install, upgrade and remove Debian binary packages.
• Find packages that contain specific files or libraries, including uninstalled ones.
• Obtain package information: version, contents, dependencies, integrity, installation status.
• Understand the purpose and capabilities of apt.

Tools and files: /etc/apt/sources.list, dpkg, dpkg-reconfigure, apt-get, apt-cache.

The .deb format and dpkg

The .deb format emerged as the standard for distributing compiled software on Debian systems. The dpkg tool works with this format directly. It is used on Debian itself and all its derivatives, including Ubuntu.

dpkg handles installation, configuration, maintenance and removal of packages. APT works on top of dpkg, adding dependency resolution and repository support — it does not replace dpkg.

Installing and upgrading packages

dpkg -i PACKAGENAME.deb

Before installing, dpkg checks whether an older version is already present. If so, the package is upgraded. Otherwise it is installed fresh.

Dependencies in dpkg

dpkg checks for dependencies when installing. If required packages are missing, installation fails with a list of unmet dependencies. dpkg cannot resolve dependencies on its own — the required .deb files must be found and installed manually.

Example dependency error:

dpkg: dependency problems prevent configuration of openshot-qt:
 openshot-qt depends on fonts-cantarell; however:
  Package fonts-cantarell is not installed.

The --force flag bypasses dependency warnings during removal, but this is dangerous: the system may end up in a broken state.

Removing packages

dpkg -r PACKAGENAME

dpkg will not remove a package if another installed package depends on it. To remove both at once, list them with a space:

dpkg -r unzip file-roller

When removing with -r, configuration files stay on the system. To remove the package along with all its config files, use the -P (purge) flag:

dpkg -P PACKAGENAME

Viewing package information

dpkg -I PACKAGENAME.deb

The -I flag (uppercase i) shows details of a .deb file: version, dependencies, description. This works on a file that is not yet installed.

Listing installed packages and their files

Show all installed packages:

dpkg --get-selections

Show the files installed by a specific package:

dpkg -L PACKAGENAME

Example output:

# dpkg -L unrar
/.
/usr
/usr/bin
/usr/bin/unrar-nonfree
/usr/share/doc/unrar/changelog.Debian.gz

Finding the owner of a file

To find which package owns a specific file on the system:

dpkg-query -S /usr/bin/unrar-nonfree
# unrar: /usr/bin/unrar-nonfree

dpkg-query -S only works with files that are already installed. To search across uninstalled packages use apt-file search.

Reconfiguring a package

When a package is installed, it runs a post-install script that sets up configuration files and asks the user questions. If the configuration is broken or you need to change the original answers, run:

dpkg-reconfigure PACKAGENAME

The utility backs up old configs, unpacks fresh ones and re-runs the post-install script as if the package were being installed for the first time. Example:

dpkg-reconfigure tzdata

Advanced Package Tool (apt)

APT simplifies package installation, upgrade and removal by adding automatic dependency resolution and remote repository support. It is a layer on top of dpkg, not a replacement.

Main APT utilities:

• apt-get — install, upgrade and remove packages.
• apt-cache — search and retrieve information from the package index.
• apt-file — search for files inside packages.
• apt — combines the most commonly used apt-get and apt-cache commands. For the exam you need to know apt-get and apt-cache, since apt may not be available on every system.

APT requires a network connection to download packages and update indexes.

Updating the package index

Before installing or upgrading packages, update the local index:

apt-get update
# or
apt update

This downloads fresh package lists from the repositories described in /etc/apt/sources.list and files in /etc/apt/sources.list.d/.

Installing, upgrading and removing via apt-get

Install a package (with automatic dependency resolution):

apt-get install PACKAGENAME

Upgrade all installed packages to the latest versions from the repositories:

apt-get upgrade
# or
apt upgrade

Upgrade a specific package:

apt-get upgrade PACKAGENAME

Remove a package:

apt-get remove PACKAGENAME
# or
apt remove PACKAGENAME

Removing with remove leaves configuration files on the system. To remove a package along with its configs, use purge:

apt-get purge PACKAGENAME
# or
apt-get remove --purge PACKAGENAME

Fix a broken installation caused by unmet dependencies:

apt-get install -f

Local package cache

When a package is downloaded, the .deb file is saved to the local cache: /var/cache/apt/archives/. Partially downloaded files go to /var/cache/apt/archives/partial/. The cache can grow large over time; clean it with:

apt-get clean
# or
apt clean

Searching packages with apt-cache

Search for a package by name, description or files:

apt-cache search PATTERN
# or
apt search PATTERN

Get detailed information about a package (version, dependencies, description), similar to dpkg -I:

apt-cache show PACKAGENAME
# or
apt show PACKAGENAME

The sources.list file

APT takes the list of package sources from /etc/apt/sources.list. It can be edited with any text editor.

A typical entry:

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

Entry syntax: archive_type URL distribution components.

Archive type:

• deb — binary packages (ready to run).
• deb-src — source packages.

Ubuntu components:

• main — officially supported open-source packages.
• restricted — officially supported proprietary software (e.g. drivers).
• universe — community-maintained packages.
• multiverse — non-free or patent-encumbered software.

Debian components:

• main — packages compliant with the DFSG, considered part of the distribution.
• contrib — DFSG-compliant packages that depend on non-free components.
• non-free — packages that do not comply with the DFSG.
• security — security updates.
• backports — newer versions of main packages for the stable release.

Lines beginning with # are comments and are ignored. After adding a new entry run apt-get update.

The sources.list.d directory

Instead of editing the main file you can add individual .list files to /etc/apt/sources.list.d/. The syntax inside is the same. Example file buster-backports.list:

deb http://deb.debian.org/debian buster-backports main contrib non-free
deb-src http://deb.debian.org/debian buster-backports main contrib non-free

apt-file: package contents and file search

apt-file may not be installed by default. Install and initialise it:

apt-get install apt-file
apt-file update

Show all files contained in a package (including uninstalled ones):

apt-file list PACKAGENAME

Find which package contains a file (including in uninstalled packages):

apt-file search FILENAME

Example:

apt-file search libSDL2.so
# libsdl2-dev: /usr/lib/x86_64-linux-gnu/libSDL2.so

The difference between apt-file search and dpkg-query -S: the former searches all packages including uninstalled ones; the latter only sees files from already installed packages.

Exam command reference

Typical exam questions

What is the difference between -r and -P in dpkg? -r removes the package but leaves configuration files. -P (purge) removes the package along with all its configs. The same distinction applies to apt-get remove and apt-get purge.

What is the difference between dpkg-query -S and apt-file search? dpkg-query -S only works with installed packages. apt-file search searches across all packages, including those not yet installed.

Can you remove a package that another package depends on? No. dpkg -r will refuse. You must remove the dependent package first, or remove both at once with dpkg -r pkg1 pkg2. The --force flag bypasses the check but is dangerous.

What does apt-get install -f do? It fixes an interrupted or incomplete installation by installing missing dependencies. The -f flag stands for --fix-broken.

What is the difference between deb and deb-src in sources.list? deb points to a repository with binary packages; deb-src points to one with source code.

Why use dpkg-reconfigure? To re-run the post-install configuration of a package, for example after the config is broken or to change the original setup answers.

Where does APT store downloaded .deb files? In /var/cache/apt/archives/. The cache can be cleared with apt-get clean.

Exercises

Guided Exercises

1. Which command installs a package named package.deb with dpkg?

dpkg -i package.deb

2. Find which package owns the file 7zr.1.gz using dpkg-query.

dpkg-query -S 7zr.1.gz

3. Can you remove the unzip package with dpkg -r unzip if file-roller depends on it? If not, how do you do it correctly?

dpkg -r unzip file-roller

4. How do you use apt-file to find which package contains the file /usr/bin/unrar?

apt-file search /usr/bin/unrar

5. Which apt-cache command shows information about the gimp package?

apt-cache show gimp

Explorational Exercises

1. Write a sources.list entry for a Debian source-package repository.

There is a source-code repository for the xenial distribution at http://us.archive.ubuntu.com/ubuntu/, component universe. Which line should be added to /etc/apt/sources.list?

deb-src http://us.archive.ubuntu.com/ubuntu/ xenial universe

2. Find the package that provides the header file zzip-io.h.

A compilation error says the header file zzip-io.h is missing from the system. How do you find which package provides it?

apt-file search zzip-io.h

3. Force-remove a package with dependants using dpkg.

How do you use dpkg to ignore the dependency warning and remove a package even if other packages depend on it?

4. Get detailed information about the midori package.

apt-cache show midori

5. Which command should be run before installing or upgrading packages to ensure the index is up to date?

apt-get update

Related topics

• 102.3 Manage Shared Libraries — shared libraries that packages depend on
• 102.5 Use RPM and YUM Package Management — equivalent package management on RPM-based systems

LPIC-1 Study Notes | Topic 101: System Architecture