Package Management
Ubuntu features a comprehensive package management system for installing, upgrading, configuring, and removing software. In addition to providing access to an organized base of over 60,000 software packages for your Ubuntu computer, the package management facilities also feature dependency resolution capabilities and software update checking.
Several tools are available for interacting with Ubuntu’s package management system, from simple command-line utilities which may be easily automated by system administrators, to a graphical interface which is easy to use by those new to Ubuntu.
Introduction
Ubuntu’s package management system is derived from the same system used by the Debian GNU/Linux distribution. The package files contain all of the necessary files, meta-data, and instructions to implement a particular functionality or software application on your Ubuntu computer.
Debian package files typically have the extension .deb , and usually exist in repositories which are collections of packages found online or on physical media, such as CD-ROM discs. Packages are normally in a pre-compiled binary format; thus installation is quick and requires no compiling of software.
Many packages use dependencies. Dependencies are additional packages required by the principal package in order to function properly. For example, the speech synthesis package festival depends upon the package alsa-utils , which is a package supplying the ALSA sound library tools needed for audio playback. In order for festival to function, it and all of its dependencies must be installed. The software management tools in Ubuntu will do this automatically.
The apt command is a powerful command-line tool, which works with Ubuntu’s Advanced Packaging Tool (APT) performing such functions as installation of new software packages, upgrade of existing software packages, updating of the package list index, and even upgrading the entire Ubuntu system.
Some examples of popular uses for the apt utility:
Install a Package: Installation of packages using the apt tool is quite simple. For example, to install the nmap network scanner, type the following:
Remove a Package: Removal of a package (or packages) is also straightforward. To remove the package installed in the previous example, type the following:
Multiple Packages: You may specify multiple packages to be installed or removed, separated by spaces.
Scripting: While apt is a command-line tool, it is intended to be used interactively, and not to be called from non-interactive scripts. The apt-get command should be used in scripts (perhaps with the —quiet flag). For basic commands the syntax of the two tools is identical.
Also, adding the —purge option to apt remove will remove the package configuration files as well. This may or may not be the desired effect, so use with caution.
Update the Package Index: The APT package index is essentially a database of available packages from the repositories defined in the /etc/apt/sources.list file and in the /etc/apt/sources.list.d directory. To update the local package index with the latest changes made in the repositories, type the following:
Upgrade Packages: Over time, updated versions of packages currently installed on your computer may become available from the package repositories (for example security updates). To upgrade your system, first, update your package index as outlined above, and then type:
For information on upgrading to a new Ubuntu release see Upgrading.
Actions of the apt command, such as installation and removal of packages, are logged in the /var/log/dpkg.log log file.
For further information about the use of APT, read the comprehensive APT User’s Guide or type:
Aptitude
Launching Aptitude with no command-line options will give you a menu-driven, text-based front-end to the Advanced Packaging Tool (APT) system. Many of the common package management functions, such as installation, removal, and upgrade, can be performed in Aptitude with single-key commands, which are typically lowercase letters.
Aptitude is best suited for use in a non-graphical terminal environment to ensure proper functioning of the command keys. You may start the menu-driven interface of Aptitude as a normal user by typing the following command at a terminal prompt:
When Aptitude starts, you will see a menu bar at the top of the screen and two panes below the menu bar. The top pane contains package categories, such as New Packages and Not Installed Packages. The bottom pane contains information related to the packages and package categories.
Using Aptitude for package management is relatively straightforward, and the user interface makes common tasks simple to perform. The following are examples of common package management functions as performed in Aptitude:
Install Packages: To install a package, locate the package via the Not Installed Packages package category, by using the keyboard arrow keys and the ENTER key. Highlight the desired package, then press the + key. The package entry should turn green, indicating that it has been marked for installation. Now press g to be presented with a summary of package actions. Press g again, and downloading and installation of the package will commence. When finished, press ENTER, to return to the menu.
Remove Packages: To remove a package, locate the package via the Installed Packages package category, by using the keyboard arrow keys and the ENTER key. Highlight the desired package you wish to remove, then press the — key. The package entry should turn pink, indicating it has been marked for removal. Now press g to be presented with a summary of package actions. Press g again, and removal of the package will commence. When finished, press ENTER, to return to the menu.
Update Package Index: To update the package index, simply press the u key. Updating of the package index will commence.
Upgrade Packages: To upgrade packages, perform the update of the package index as detailed above, and then press the U key to mark all packages with updates. Now press g whereby you’ll be presented with a summary of package actions. Press g again, and the download and installation will commence. When finished, press ENTER, to return to the menu.
The first column of the information displayed in the package list in the top pane, when actually viewing packages lists the current state of the package, and uses the following key to describe the state of the package:
i: Installed package
c: Package not installed, but package configuration remains on the system
p: Purged from system
v: Virtual package
B: Broken package
u: Unpacked files, but package not yet configured
C: Half-configured — Configuration failed and requires fix
H: Half-installed — Removal failed and requires a fix
To exit Aptitude, simply press the q key and confirm you wish to exit. Many other functions are available from the Aptitude menu by pressing the F10 key.
Command Line Aptitude
You can also use Aptitude as a command-line tool, similar to apt. To install the nmap package with all necessary dependencies, as in the apt example, you would use the following command:
To remove the same package, you would use the command:
Consult the man pages for more details of command-line options for Aptitude.
dpkg is a package manager for Debian-based systems. It can install, remove, and build packages, but unlike other package management systems, it cannot automatically download and install packages or their dependencies. Apt and Aptitude are newer, and layer additional features on top of dpkg. This section covers using dpkg to manage locally installed packages:
To list all packages in the system’s package database, including all packages, installed and uninstalled, from a terminal prompt type:
Depending on the number of packages on your system, this can generate a large amount of output. Pipe the output through grep to see if a specific package is installed:
Replace apache2 with any package name, part of a package name, or a regular expression.
To list the files installed by a package, in this case the ufw package, enter:
If you are not sure which package installed a file, dpkg -S may be able to tell you. For example:
The output shows that the /etc/host.conf belongs to the base-files package.
Many files are automatically generated during the package install process, and even though they are on the filesystem, dpkg -S may not know which package they belong to.
You can install a local .deb file by entering:
Change zip_3.0-4_amd64.deb to the actual file name of the local .deb file you wish to install.
Uninstalling a package can be accomplished by:
Uninstalling packages using dpkg, in most cases, is NOT recommended. It is better to use a package manager that handles dependencies to ensure that the system is in a consistent state. For example, using dpkg -r zip will remove the zip package, but any packages that depend on it will still be installed and may no longer function correctly.
For more dpkg options see the man page: man dpkg .
APT Configuration
Configuration of the Advanced Packaging Tool (APT) system repositories is stored in the /etc/apt/sources.list file and the /etc/apt/sources.list.d directory. An example of this file is referenced here, along with information on adding or removing repository references from the file.
You may edit the file to enable repositories or disable them. For example, to disable the requirement of inserting the Ubuntu CD-ROM whenever package operations occur, simply comment out the appropriate line for the CD-ROM, which appears at the top of the file:
Extra Repositories
In addition to the officially supported package repositories available for Ubuntu, there exist additional community-maintained repositories which add thousands more packages for potential installation. Two of the most popular are the universe and multiverse repositories. These repositories are not officially supported by Ubuntu, but because they are maintained by the community they generally provide packages which are safe for use with your Ubuntu computer.
Packages in the multiverse repository often have licensing issues that prevent them from being distributed with a free operating system, and they may be illegal in your locality.
Be advised that neither the universe or multiverse repositories contain officially supported packages. In particular, there may not be security updates for these packages.
Many other package sources are available, sometimes even offering only one package, as in the case of package sources provided by the developer of a single application. You should always be very careful and cautious when using non-standard package sources, however. Research the source and packages carefully before performing any installation, as some package sources and their packages could render your system unstable or non-functional in some respects.
By default, the universe and multiverse repositories are enabled but if you would like to disable them edit /etc/apt/sources.list and comment the following lines:
Automatic Updates
The unattended-upgrades package can be used to automatically install updated packages and can be configured to update all packages or just install security updates. First, install the package by entering the following in a terminal:
To configure unattended-upgrades, edit /etc/apt/apt.conf.d/50unattended-upgrades and adjust the following to fit your needs:
Certain packages can also be blacklisted and therefore will not be automatically updated. To blacklist a package, add it to the list:
The double “//” serve as comments, so whatever follows “//” will not be evaluated.
To enable automatic updates, edit /etc/apt/apt.conf.d/20auto-upgrades and set the appropriate apt configuration options:
The above configuration updates the package list, downloads, and installs available upgrades every day. Those actions are triggered by timer units at a set time but with a random delay: apt-daily.timer and apt-daily-upgrades.timer . These timers activate the correspondent services that run /usr/lib/apt/apt.systemd.daily script.
However, it may happen that if the server is off at the time the timer unit elapses, the timer will be triggered immediately at the next startup. As a result, they will often run on system startup
and thereby cause immediate activity and hold the apt-lock.
In many cases that is beneficial, but in some cases it might be counter-productive. Examples are administrators with many shut down machines or VM images that are only started for some quick action that then is delayed or even blocked by the unattended upgrades. To adapt this behaviour, we can change/override the configuration of both apt’s timer units [ apt-daily-upgrade.timer, apt-daily.timer ]. To do so use systemctl edit and override the Persistent attribute like Persistent=delay (example of such an override):
The local download archive is cleaned every week. On servers upgraded to newer versions of Ubuntu, depending on your responses, the file listed above may not be there. In this case, creating a new file of this name should also work.
You can read more about apt Periodic configuration options in the apt.conf(5) manpage and in the /usr/lib/apt/apt.systemd.daily script header.
The results of unattended-upgrades will be logged to /var/log/unattended-upgrades .
Notifications
Configuring Unattended-Upgrade::Mail in /etc/apt/apt.conf.d/50unattended-upgrades will enable unattended-upgrades to email an administrator detailing any packages that need upgrading or have problems.
Another useful package is apticron. apticron will configure a cron job to email an administrator information about any packages on the system that have updates available, as well as a summary of changes in each package.
To install the apticron package, in a terminal enter:
Once the package is installed edit /etc/apticron/apticron.conf , to set the email address and other options:
References
Most of the material covered in this chapter is available in man pages, many of which are available online.
The InstallingSoftware Ubuntu wiki page has more information.
For more dpkg details see the dpkg man page.
The APT User’s Guide and apt man page contain useful information regarding apt usage.
For more info about systemd timer units (and systemd in general), visit systemd man page and systemd.timer man page.
See the aptitude user’s manual for more aptitude options.
The Adding Repositories HOWTO (Ubuntu Wiki) page contains more details on adding repositories.
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