# Package Managers

Linux package managers allow software to be managed on your favorite distribution, that is installed, configured, updated and removed. Package managers do so by handling packages - archives that contain the binary files, configuration files, man/info pages, copyright information, information about dependencies, ...

Every Linux distribution is different in terms of how software is installed. Different Linux distributions use different installation file types, package managers, and commands for installation. Even within a single form of Linux, there are different types of package managers.

In this course the focus will lie on Debian based system's which typically use the package managers dpkg, APT, aptitude, apt and snap.

# Debian and it's Packages

Debian packages can either be downloaded manually or fetched automatically from a repository if the package manager supports this feature.

Packages generally contain all of the files necessary to implement a set of related commands or features. There are two types of Debian packages:

• Binary packages, which contain executables, configuration files, man/info pages, copyright information, and other documentation. These packages are distributed in a Debian-specific archive format; they are usually distinguished by having a .deb file extension. Binary packages can be unpacked using the Debian utility dpkg (possibly via a frontend like aptitude).
• Source packages, which consist of a .dsc file describing the source package (including the names of the following files), a .orig.tar.gz file that contains the original unmodified source in gzip-compressed tar format and usually a .diff.gz file that contains the Debian-specific changes to the original source. The utility dpkg-source packs and unpacks Debian source archives. (The program apt-get can be used as a frontend for dpkg-source.)

Debian files are usually downloaded by package managers from a software repository. A repository is a collection of Debian files that typically comes from a server or other location. Package managers access these repositories and download the requested Debian file. Then, the package manager installs the package. A package manager is software used to handle the installation, removal, configuration, and updating of programs and drivers on a computer system.

If a Debian file is not downloaded from a repository, then the user downloaded or created a Debian file. The local file can still be installed using a package manager such as dpkg; Debian files are not required to come from a repository, although most do.

Installation of software by the package system uses "dependencies" which are carefully designed by the package maintainers. These dependencies are documented in the control file associated with each package.

For example, the package containing the GNU C compiler gcc "depends" on the package binutils which includes the linker and assembler. If a user attempts to install gcc without having first installed binutils, the package management system dpkg will send an error message that it also needs binutils, and stop installing gcc.

There are multiple tools that are used to manage Debian packages, from graphic or text-based interfaces to the low level tools used to install packages. All the available tools rely on the lower level tools to properly work.

It is important to understand that the higher level package management tools such as aptitude rely on APT which, itself, relies on dpkg to manage the packages in the system.

# DPKG - Debian Package

dpkg (Debian Package) is the main package management program for debian based Linux distributions. dpkg is the software at the base of the package management system in the free operating system Debian and its numerous derivatives. dpkg is used to install, remove, and provide information about .deb packages.

dpkg itself is a low level tool and therefore does not handle things such as dependencies automatically. Installing packages that depend on multiple other packages makes using dpkg the less preferred choice.

dpkg was originally created by Ian Murdock in January 1994 as a Shell script, Matt Welsh, Carl Streeter and Ian Murdock then rewrote it in Perl, and then later the main part was rewritten in C by Ian Jackson in 1994.

Installing a package using dpkg can be achieved using the command dpkg --install <packagefile>.deb.

For example (after downloading the package file from http://security.ubuntu.com/ubuntu/pool/universe/s/sl/ (opens new window)):

[bioboost@linux][~]$ dpkg --install sl_5.02-1_amd64.deb
 
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Selecting previously unselected package sl.
(Reading database ... 223821 files and directories currently installed.)
Preparing to unpack sl_5.02-1_amd64.deb ...
Unpacking sl (5.02-1) ...
Setting up sl (5.02-1) ...
Processing triggers for man-db (2.9.1-1) ...

Basically this was a walk in the park because the sl package has no uncommon dependencies. They are most likely already installed on your system. If not, dpkg will throw an error and you will need to solve the dependencies manually or use a more high-level package manager.

# APT

APT (Advanced Package Tool) is a set of tools that allow package management on a debian based system. It contains tools such as apt-get and apt-cache. apt-get provides a simple way to retrieve and install packages from multiple sources using the command line. Unlike dpkg, apt-get does not understand .deb files, it works with the packages proper name and can only install .deb archives from a source specified in /etc/apt/sources.list. apt-get will call dpkg directly after downloading the .deb archives from the configured sources in order to install the package.

APT, a higher level tool, is more commonly used than dpkg as it can fetch packages from remote locations and deal with complex package relations, such as dependency resolution.

Some common ways to use apt-get and apt-cache are:

• apt-get update: update the list of package known by your system.
• apt-get upgrade: upgrade all the packages on your system (without installing extra packages or removing packages).
• apt-get install foo: install the foo package and all its dependencies.
• apt-get remove foo: remove the foo package from your system but leave configuration files as is.
• apt-get purge foo: remove the foo package and its configuration files from your system.
• apt-get dist-upgrade: upgrade all the packages on your system, and, if needed for a package upgrade, install extra packages or remove packages.
• apt-cache search foo: search the repository (local cache) for a package called foo
• apt-cache show foo: show detailed information about the foo package

# And then there was apt

The original APT (not the same as the apt command), has the problem that it has many low-level commands with many functionalities which are perhaps never used by an average Linux user. On the other hand, the most commonly used package management commands are scattered across apt-get and apt-cache.

The apt commands have been introduced to solve this problem. apt consists of some of the most widely used features from apt-get and apt-cache and even dpkg, leaving aside obscure and seldom used features. It can also manage the apt.conf file.

With apt, you don't have to fiddle your way from apt-get commands to apt-cache. apt is more structured and provides you with necessary options needed to manage packages.

Bottom line: apt = most common used command options from apt-get and apt-cache.

• To list all the installed packages on your system you can use the apt list --installed command. You can also list all packages or list packages that are upgradable by using the --upgradable flag.

[bioboost@linux][~]$ apt list --installed
 
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Listing...
accountsservice/focal-security,now 0.6.55-0ubuntu12~20.04.4 amd64 [installed,automatic]
acl/focal,now 2.2.53-6 amd64 [installed,automatic]
acpi-support/focal,now 0.143 amd64 [installed,automatic]
acpid/focal,now 1:2.0.32-1ubuntu1 amd64 [installed,automatic]
adduser/focal,focal,now 3.118ubuntu2 all [installed,automatic]
adwaita-icon-theme/now 3.36.1-2ubuntu0.20.04.2 all [installed,local]
aisleriot/focal,now 1:3.22.9-1 amd64 [installed,automatic]
...

• To update your local package cache, use the command apt update. It will also show the number of upgradable packages installed on your system.

[bioboost@linux][~]$ apt update
 
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Hit:1 https://download.docker.com/linux/ubuntu focal InRelease
Hit:2 http://dl.google.com/linux/chrome/deb stable InRelease
Hit:3 http://ppa.launchpad.net/kicad/kicad-dev-nightly/ubuntu focal InRelease
Hit:4 http://be.archive.ubuntu.com/ubuntu focal InRelease
Get:5 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]
Get:6 http://security.ubuntu.com/ubuntu focal-security/main amd64 DEP-11 Metadata [27,6 kB]
Get:7 http://security.ubuntu.com/ubuntu focal-security/universe amd64 DEP-11 Metadata [61,1 kB]
Get:8 http://security.ubuntu.com/ubuntu focal-security/multiverse amd64 DEP-11 Metadata [2.468 B]
Fetched 205 kB in 1s (186 kB/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up to date.

• To search for a package, use the apt search <pkgname> command.

[bioboost@linux][~]$ apt search cow
 
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Sorting... Done
Full Text Search... Done
averell/focal,focal 1.2.5-1.1 all
  incredibly stupid web server

cowbell/focal 0.2.7.1-7build2 amd64
  An easy-to-use tag editor for your music files

cowbuilder/focal 0.88 amd64
  pbuilder running on cowdancer

...

• To install a package, use the apt install <pkgname> command.

[bioboost@linux][~]$ apt install sl
 
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Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  sl
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 12,7 kB of archives.
After this operation, 60,4 kB of additional disk space will be used.
Get:1 http://be.archive.ubuntu.com/ubuntu focal/universe amd64 sl amd64 5.02-1 [12,7 kB]
Fetched 12,7 kB in 0s (110 kB/s)
Selecting previously unselected package sl.
(Reading database ... 223496 files and directories currently installed.)
Preparing to unpack .../archives/sl_5.02-1_amd64.deb ...
Unpacking sl (5.02-1) ...
Setting up sl (5.02-1) ...
Processing triggers for man-db (2.9.1-1) ...

• To remove a package (leaving the configuration files in tact), use the apt remove <pkgname> command. To purge a package (also removing the configuration files), use the apt purge <pkgname> command.

[bioboost@linux][~]$ apt purge sl
 
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Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
  sl*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 60,4 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 223519 files and directories currently installed.)
Removing sl (5.02-1) ...
Processing triggers for man-db (2.9.1-1) ...

Some other useful options might be:

• show <pkgname>: Show some detailed information about a package. Works like apt-cache show but hides some details that people are less likely to care about (like the hashes).
• upgrade: install available upgrades of all packages currently installed on the system. New packages will be installed if required to satisfy dependencies, but existing packages will never be removed.
• full-upgrade: upgrade all the packages on your system, and, if needed for a package upgrade, remove packages.
• edit-sources: edit sources.list using $EDITOR.

# Aptitude

Aptitude is a package manager for Debian GNU/Linux systems that provides a frontend to the apt package management infrastructure. Aptitude is a text-based interface using the curses library, it can be used to perform management tasks in a fast and easy way.

• aptitude offers easy access to all versions of a package.
• aptitude makes it easy to keep track of obsolete software by listing it under "Obsolete and Locally Created Packages".
• aptitude includes a fairly powerful system for searching particular packages and limiting the package display. Users familiar with mutt will pick up quickly, as mutt was the inspiration for the expression syntax.
• aptitude can be used to install the predefined tasks available.
• aptitude in full screen mode has su functionality embedded and can be run by a normal user. It will call su (and ask for the root password, if any) when you really need administrative privileges

You can launch the graphical frontend by running it from the terminal:

[bioboost@linux][~]$ aptitude
 
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Or you can use most apt options from the command line such as aptitude search, aptitude install, aptitude purge and so on.

# Snap

Snap is a software packaging and deployment system developed by Canonical for operating systems that use the Linux kernel. The packages, called snaps, and the tool for using them, snapd, work across a range of Linux distributions.

Some of the advantages of snap are that:

• It allows upstream software developers to distribute their applications directly to users.
• Snaps are self-contained applications running in a sandbox with mediated access to the host system.

The Snap Store allows developers to publish their applications directly to users. With traditional Linux package management approaches like APT, the applications are packaged and distributed as part of the operating system. This creates a delay between application development and its deployment for end-users. In contrast, application developers can publish their applications in the Snap Store and get them directly to users without any intervention from distribution maintainers.

All apps uploaded to the Snap Store undergo automatic testing, including a malware scan. However, Snap apps do not receive the same level of verification as software in the regular Ubuntu archives.

While snap was originally released for cloud applications, it was later ported to work for Internet of Things devices and desktop applications too.

Checkout the snap store at https://snapcraft.io/ (opens new window).

# App Images

There are ways to install software in Ubuntu or any other Linux distribution. Downloading .deb files, using package managers like apt or generating binaries from source. Recently, you might have noticed that some applications are downloadable with a .AppImage extension.

Some examples are:

• Ultimaker Cura which can be found at ultimaker.com (opens new window).
• FreeCAD which can be found at freecadweb.org (opens new window).
• Insomnia which can be found at insomnia.rest (opens new window).

Many AppImages can be found at appimage.github.io (opens new window) or at github.com/AppImage/AppImageKit/wiki/AppImages (opens new window).

# What is an AppImage

For years, DEB packages for Debian/Ubuntu based Linux distributions and RPM for Fedora/SUSE based Linux distributions have ruled the distro world.

While these packages provide a convenient way of installing software for their respective distribution users, it is not the most convenient solution for the application developer. The developers have to create multiple packages for multiple distributions. This is where AppImage comes into the picture.

AppImage is a universal software package format. By packaging the software in AppImage, the developer provides just one file for several distributions - if not all - most modern Linux distributions

A typical Linux application installation will create files at various places, requiring root permission to make these changes to the system.

AppImage doesn’t do that. In fact, AppImage doesn’t really install anything. It is a compressed image with all the dependencies and libraries needed to run the desired software.

You execute the AppImage file, you run the software. There is no extraction, no installation. You delete the AppImage file, the software is removed.

Some advantageous features of AppImage are:

• Distribution agnostic: Can run on various different Linux distributions
• No need of installing and compiling software: Just click and play
• No need of root permission: System files are not touched
• Portability: Can be run anywhere including live disks
• Apps are in read only mode
• Software are removed just by deleting the AppImage file
• Applications packaged in AppImage are not sandboxed by default.

# Running AppImages

One does not need to install anything to be able to run an AppImage. All you need to do is:

1. Download the AppImage file
2. Make it executable using chmox u+x <appimage>
3. Execute it ./<appimage>

Download for example the latest release of the Insomnia client:

cd ~
mkdir apps
cd apps
wget https://github.com/Kong/insomnia/releases/download/core%402021.6.0/Insomnia.Core-2021.6.0.AppImage
chmod u+x Insomnia.Core-2021.6.0.AppImage
./Insomnia.Core-2021.6.0.AppImage
 
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# Challenges

Find all the info you need in the man-pages. Document the commands you used for solving the challenge. Try to use as little google as possible.

Mark challenges using a ✅ once they are finished.

# ❌ Cowsay

Download the .deb package for cowsay and install it using dpkg. You can find the package at https://packages.debian.org/sid/all/cowsay/download (opens new window).

Run it once it's installed. What does it do ?

# ❌ Nmap

Install the nmap package using apt.

Port scan the server sivir.devbit.be. Make sure you are connected to the Devbit network. What services are running on this machine?

# ❌ NodeJS

Install snap using apt. Next use snap to install nodejs.

Now launch node and tryout the following little code snippet:

console.log("Hello World from JavaScript");
 
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# ❌ Dhcpdump

Install the dhcpdump and try to capture some DHCP traffic in the network. Work together with another student and try to capture the DHCP request of his/her laptop. Find out what the MAC Address is and check it using the ip or ipconfig tool.

# ❌ MQTT

Find a command line tool that allows you to publish messages to an MQTT broker. Use it to send your name to the topic linux/students. Use the broker mqtt.devbit.be.