Ubuntu and Debian Package Management Tutorial

Package management is one of the components that contribute to the steep learning curve of using a linux system for a majority of first time linux users. Coming from the GUI environment of Windows or MacOS where installing/removing applications consist of clicking on Next -> Next -> I Agree -> Install/Uninstall, the terminal based package managers might be intimidating. And this issue is not constrained to first time users either. Even though I have used a linux system as my primary OS for several years now, I end up googling the errors and copy-pasting the answers from SO without the slightest idea of what I am doing most of the times. Hence, I am writing this blog post to be a glossary of the commands that we can use to fix our own package errors or to know what each command is doing even if we end up copy-pasting from the internet to fix our problems.

RHEL-based distributions:

• Packaging format: RPM
• Tools: rpm, yum

Debian and Ubuntu based distributions:

• Packaging format: .deb
• Tools: apt, apt-get, dpkg

In this blog post, I will be covering the Debian/Ubuntu based distributions, since well, I am a Ubuntu user.

Debian/Ubuntu Package Management Tools

• apt-get:

  apt-get is used to interface with remote repositories. Main difference with apt is that apt pulls from the remote repository into a local cache and then uses this copy in the cache. apt-get uses the same methodology but refreshes the cache every time.

• apt-cache:

  Like discussed earlier, this is the local cache that apt uses.

• aptitude:

  Has both capabilities of the above tools. Can be dropped in place of both apt-get and apt-cache.

• dpkg:

  The above tools are used to manage and pull packages from remote repositories. dpkg operates on the actual .deb files. It cannot resolve dependencies like apt-*.

• tasksel:

  This is used for grouping of similarly related packages. For eg, if you want a MEAN stack setup, you can use tasksel to install all required packages instead of installing each of them individually.

Commands

1. sudo apt-get update

   Updating the local cache with the latest info about the remote repositories.

2. sudo apt-get upgrade

   Upgrade any component that do not require you to remove any other packages.

3. sudo apt-get dist-upgrade

   Upgrade components when you are OK with removing/swapping other packages.

4. apt-cache search _package_

   Search for package in the repositories. You will have to run sudo apt-get update before doing this.

5. sudo apt-get install _package_

6. sudo apt-get install _package1_ _package2_

7. sudo apt-get install _package=version_

   Install a specific version of the package.

8. sudo dpkg-reconfigure _package_

   Reconfigure package. Most of the packages, after you install them, they go through a configuration script that configures your system to use that particular package. Sometimes this include user prompts as well. If you want to do this configuration yourself after installation or rerun the configuration, use this command.

9. apt-get install -s _package_

   Dry-run installation. Using this command you can see all the changes that installing package might do to your system without actually doing those changes. One important note is that this command does not require sudo and hence can be used in systems where you do not have root privileges.

10. sudo dpkg --install _debfile.deb_

    Install directly from the debfile.deb file. Note that this DOES NOT resolve dependencies.

11. sudo apt-get install -f

    This command is used to fix dependency issues. While installing a package, if there are unmet dependencies, the installation will fail. If you’ve noticed, apt-* commands resolve these dependencies automatically. Whereas using dpkg to install .deb files directly does not resolve dependencies. Hence, run this command in those scenarios.

12. sudo apt-get remove _package_

    Remove the package without removing the configuration files. If you accidentally remove a package or install the same package after some time, you will need to save the configuration you did for your first installation.

13. sudo apt-get purge _package_

    Remove the package and all it’s configuration files.

14. sudo apt-get autoremove

    Remove any packages that were installed as dependencies and are no longer required. Use --purge to remove the configuration files of these packages.

15. sudo apt-get autoclean

    Remove out-of-date packages in your system that are no longer maintained in the remote repository.

16. apt-cache show _package_

    Show information about package.

17. dpkg --info _debfile.deb_

    Show information about the debfile.deb file.

18. apt-cache depends _package_

    Show dependencies of the package.

19. apt-cache rdepends _package_

    Show packages that are dependent on this package (reverse dependency)

20. apt-cache policy _package_

    If there are multiple versions of package installed, this command shows all the versions and the version being used as default.

21. dpkg -l

    Shows a list of every installed/partially-installed packages in the system. Each package is preceded by a series of characters.

    First character:

    - _u_: unknown
    - _i_: installed
    - _r_: removed
    - _p_: purged
    - _h_: version is held
    

    Second character:

    - _n_: not installed
    - _i_: installed
    - _c_: configuration files are present, but the application is uninstalled
    - _u_: unpacked. The files are unpacked, but not configured yet
    - _f_: package is half installed, meaning that there was a failure part way through an installation that halted the operation
    - _w_: package is waiting for a trigger from a separate package
    - _p_: package has been triggered by another package
    

    Third character:

    - _r_: re-installation is required. Package is broken.
    

22. dpkg -l _regex_

    Search for all packages matching the regex.

23. dpkg -L _package_

    List all files controlled by this package.

24. dpkg -S _/path/to/file_

    This is the inverse of -L, which gives a list of all files controlled by a package. -S prints the package that is controlling this file.

25. dpkg --get-selections > ~/packagelist.txt

    Export the list of installed packages to ~/packagelist.txt file which can be used to restore in a new system. This is analogous to requirements.txt file in python.

26. sudo add-apt-repository _ppa:owner_name/ppa_name_

    This is used to add a PPA (Personal Package Archives). When you cannot find the required package in the default set of repositories and is available in another repository, we can add that PPA and install packages from there. This is specific to Ubuntu systems as of now. Before installing packages from the newly added repository, update the local cache with sudo apt-get update. Usually PPAs have a smaller scope than a repository.

27. Adding a new repository:
    • Edit the /etc/apt/sources.list file

    • Create a new /etc/apt/sources.list.d/new_repo.list file (Must end with .list)

      Inside the file, add the new repository with the following format. deb_or_deb-src url_of_repo release_code_name_or_suite component_names

    • deb or deb-src: This identifies the type of repository. It can be either deb (for conventional repositories) or deb-src (for source repositories)
    • url: URL of the repository.
    • release_code_name or suite: Code name of your distribution’s release
    • component_names: Labels for the source.

28. Exporting a package list:

    If you want to setup a new system with all the packages from the old system, you first have to export the package details from the old system and install it in the new system.

    • dpkg --get-selections > ~/packagelist.txt: Export all package names
    • mkdir ~/sources
    • cp -R /etc/apt/sources.list* ~/sources: Backup your sources list.
    • apt-key exportall > ~/trusted_keys.txt: Backup your trusted keys
29. Importing a package list:
    • sudo apt-key add ~/trusted_keys.txt
    • sudo cp -R ~sources/* /etc/apt/
    • sudo dpkg --clear-selections: Clear all non essential packages from the system for a clean slate.
    • sudo apt-get update
    • sudo apt-get install dselect: Install dselect tool
    • sudo dselect update
    • sudo dpkg --set-selections < packagelist.txt: Import from the package list.
    • sudo apt-get dselect-upgrade