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How to Reinstall Apt on Ubuntu/Debian
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1. Overview
Almost every operating system comes with a package management system for installing, upgrading, managing, and uninstalling software. The same is true for Ubuntu, which provides many tools for interacting with its package management system.
For installing a package, Ubuntu has a CLI interface for advanced users as well as a Graphical interface for new users. For example, Ubuntu has a powerful CLI tool called APT or Advanced Packaging Tool that serves our purpose.
In this article, we’ll learn about reinstalling the apt package on a Ubuntu 20.04 system.
2. Identifying the Problem
An error commonly encountered on Debian-based operating systems is “apt: command not found“. The error occurs when the apt package is uninstalled from the system. Therefore, to solve this error, we need to reinstall the apt package.
Also, note that apt is a Debian-based package. If you are still getting this error after following this article, you should check your Linux distribution. For instance, many users often try to install the apt package on an unsupported platform like Amazon Linux or CentOS. In most cases, the problem can be solved by using the proper package manager.
3. How to Install the apt Package?
Let’s first check if the apt package is present or not on our system:
Since the apt package was removed, we’re getting the command not found message.
Let’s now move on to installing back the apt package. Basically, we can use the default Software Center or an application like Gdebi for installing a .deb format file. However, in the wake of trying to install the apt package from a .deb file, we found that the Gdebi application and Ubuntu’s default Software Center cannot be used as they depend on apt.
Finally, the dpkg utility comes to the rescue and installs the apt package back into our system.
3.1. Using the dpkg Utility
dpkg is a packaging utility for Debian systems. Usually, we use dpkg to install packages already available on the system. Indeed, the apt-get command uses dpkg for installing these packages.
The official Ubuntu repository provides the apt package file for different versions of Ubuntu. We can check out the apt packages here. We have to download the file corresponding to our system OS version and processor architecture.
Since we’re using Ubuntu 20.04 for our example, we’ll download the file for Ubuntu focal 20.04 LTS. This file comes in Debian format, and we can download it using the wget utility:
After downloading the file, we can continue with installing the package using the dpkg utility. Let’s see how the dpkg utility handles the package installation:
The -i flag installs the specified package. Also, to test if the apt package installation is successful, we can try updating the local repository:
Now, this command runs smoothly. Finally, the apt package installation is successful on our system. Furthermore, we can now continue using the CLI package manager as well as Ubuntu’s Software Center.
3.2. Resolving Dependencies Issues
While installing the .deb files, we can come across some dependencies issues. In fact, we can fix this by installing these dependencies. Let’s discover the name of dependencies required for the apt package:
From the output of the above command, look for the line that says Depends:
From here, we can select the dependencies we need to install for the apt package to work.
4. Conclusion
In this article, we’ve seen how to reinstall the apt package if it is unintentionally or otherwise removed from the system. In short, we have seen how we can use the dpkg utility for fixing this issue.
Installing apt to Ubuntu [duplicate]
I accidentially deleted apt on my Ubuntu. How can I reinstall it somehow or do I need to reinstall the whole system?
2 Answers 2
You can install deb packages using the dpkg command. You can go onto an Ubuntu mirror for the version you use, then download the apt package and dependencies (you can check with dpkg-deb -I apt[. ].deb), then install it using dpkg -i apt[. ].deb.
Everything you probably need is here.
- If the version isn’t right, check this for whichever versions are available when you found this answer.
- If wget isn’t found, then just download apt*.deb from the same link.
- If it fails to find dependencies, then download the dependencies in the same manner as apt, then try again.
FYI, at time of writing I see these dependencies (on debian):
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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 that can be easily automated by system administrators, to an easy-to-use graphical interface for 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, metadata, 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 Advanced Linux Sound Architecture (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.
Advanced Packaging Tool – APT
The apt command is a powerful command-line tool, which works with Ubuntu’s Advanced Packaging Tool (APT). The commands contained within apt provide the means for installing new software packages, upgrading existing software packages, updating the package list index, and even upgrading the entire Ubuntu system.
Some examples of popular uses for the apt utility include:
Install a Package
Installation of packages using apt is quite simple. For example, to install the nmap network scanner, type the following:
Tip
You can specify multiple packages to be installed or removed, by separating them with spaces.
Remove a Package
Removal of a package (or packages) is also straightforward. To remove the package installed in the previous example, simply type:
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.
Note:
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.
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
Installed packages on your computer may periodically have upgrades available from the package repositories (e.g., security updates). To upgrade your system, first, update your package index with sudo apt update , and then type:
For details on how to upgrade to a new Ubuntu release, see our guide on 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 apt help .
Aptitude
Launching Aptitude with no command-line options will give you a menu-driven, text-based frontend to the 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 can 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 it 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 it has been marked for installation. Now press g to be presented with a summary of package actions. Press g again, and the package will be downloaded and installed. When finished, press Enter to return to the menu.
Remove Packages
To remove a package, locate it in the Installed Packages package category by using the keyboard arrow keys and the Enter key. Highlight the package you want 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 the package will be removed. When finished, press Enter to return to the menu.
Update Package Index
To update the package index, simply press the u key.
Upgrade Packages
To upgrade packages, first update the package index as detailed above, and then press the U key to mark all packages with updates. Now press g , which will present you with a summary of package actions. Press g again to begin the download and installation. When finished, press Enter to return to the menu.
The first column of information displayed in the package list (in the top pane) lists the current state of the package (when viewing packages). It uses the following key to describe the package state:
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 Aptitude manpages for full details of Aptitude’s command-line options.
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, 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 unsure 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.
Note:
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.
You can uninstall a package by:
Caution:
Uninstalling packages using dpkg , is NOT recommended in most cases. 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 manpage: man dpkg .
APT configuration
Configuration of the 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 can edit the file to enable and disable repositories. 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 are also 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.
Note:
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.
Warning:
Be advised that neither universe nor multiverse 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 packages provided by the developer of a single application. You should always be very careful and cautious when using non-standard package sources/repos, however. Research the packages and their origins carefully before performing any installation, as some packages could render your system unstable or non-functional in some respects.
By default, the universe and multiverse repositories are enabled. If you would like to disable them, edit /etc/apt/sources.list and comment out 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 excluded and therefore will not be automatically updated. To block a package, add it to the list:
Note:
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. These actions are triggered by timer units at a set time but with a random delay: apt-daily.timer and apt-daily-upgrade.timer . These timers activate the correspondent services that run the /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 this 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, which 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 <timer_unit> and override the Persistent attribute, for example with Persistent=delay :
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 the same name should also work.
Note:
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, enter the following command in a terminal:
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 Installing Software 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 the 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.