DPKG

Debian Package

What is dpkg

dpkg is the core package management tool for Debian-based Linux distributions, such as Debian itself, Ubuntu, and others. It is responsible for installing, removing, and providing information about .deb packages, which are the standard package format used in these systems. While dpkg can handle individual packages directly, it does not manage dependencies or resolve package conflicts. For instance, if you attempt to install a .deb package that requires other packages to function, dpkg will not automatically fetch or install those dependencies.

One of the key features of dpkg is its ability to manage local package installations. You can use dpkg to install packages that are downloaded directly from sources outside the official repositories, like from a file or a third-party vendor. It offers several subcommands, such as dpkg -i for installing a package, dpkg -r for removing a package, and dpkg -l for listing installed packages. This makes dpkg useful for situations where you don’t have access to an online repository or when you need fine-grained control over specific package installations.

However, dpkg is a low-level tool, and it does not handle higher-level tasks like dependency resolution or package updates. For these functions, users typically rely on tools like apt or apt-get. These tools work with repositories, automatically resolving dependencies, handling package versions, and installing any missing libraries or packages. While dpkg can install a .deb file, it’s often used in conjunction with apt to ensure that the system remains properly configured and that all necessary dependencies are installed.

Note that dpkg is used to install individually packages. The main drawback of using dpkg is missing dependencies handling

How to install dpkg

Comes pre-installed with a debian base installation.

Folder/files structure and configuration

folder-structure

1. /var/lib/dpkg/

  • Purpose: This is the main directory where dpkg keeps its database and configuration files.
  • Common Subdirectories/Files:
    • /var/lib/dpkg/status: The status file where dpkg keeps track of the installed packages and their state (installed, removed, etc.).
    • /var/lib/dpkg/info/: Contains package-specific metadata like control files, installation scripts, and files for each installed package (e.g., vlc.md5sums, vlc.list).

2. /var/cache/apt/

  • Purpose: While not directly related to dpkg, this directory is where APT (Advanced Package Tool) caches downloaded package files, which can be used later by dpkg for installation.
  • Common Subdirectories:
    • /var/cache/apt/archives/: This folder contains downloaded .deb package files that APT uses for installation (if you install a package with apt).
    • /var/cache/apt/archives/partial/: Temporary storage for partially downloaded packages.

3. /usr/share/doc/

  • Purpose: Contains documentation files for installed packages. These are generally placed here by dpkg when packages are installed.
  • Common Subdirectories:
    • /usr/share/doc/<package_name>/: Documentation folder for each package, containing README files, changelogs, and licensing information.
    • /usr/share/doc/package_name/changelog.Debian.gz: Changelog for Debian packages.

4. /etc/

  • Purpose: Configuration files for installed packages are typically placed here by dpkg.
  • Common Subdirectories:
    • /etc/apt/: APT configuration files like sources.list (repository sources), preferences, etc.
    • /etc/dpkg/: Configuration files for dpkg (e.g., dpkg.cfg).

5. /usr/bin/ and /usr/sbin/

  • Purpose: These directories are where executables (binaries) for most installed packages are stored.
  • Common Files:
    • /usr/bin/: Binaries for user-level commands.
    • /usr/sbin/: System-level binaries that require superuser privileges.

6. /var/log/apt/

  • Purpose: Contains log files for APT operations, which can provide details on installed or removed packages.
  • Common Files:
    • /var/log/apt/history.log: Logs installation and removal history of packages via APT.
    • /var/log/apt/term.log: Logs terminal output of APT commands.

7. /var/lib/dpkg/updates/

  • Purpose: Stores updates for installed packages, which dpkg uses during upgrades.
  • Common Files:
    • Temporary files used by dpkg during package upgrades, such as partial package updates.

8. /tmp/

  • Purpose: Temporary space used by dpkg and other package managers for temporary files during package installation or upgrades.
  • Common Files:
    • Temporary files generated during installations, such as unpacked files or installation logs.

9. /etc/alternatives/ (Related to alternatives system)

  • Purpose: This directory holds symbolic links that manage alternatives (e.g., different versions of java or python).
  • Usage: Tools like update-alternatives use this directory to create symbolic links for various executables, often when multiple versions of a program are installed.

Termomonlogy and Concept

    • .deb Package
      • The Debian package format, used to distribute software and system components in Debian-based systems. A .deb file contains the compiled software, configuration files, and metadata needed for installation.
    • Package
      • A collection of files and metadata bundled together in a .deb file. It includes the program, its libraries, and documentation, as well as installation scripts and configuration files.
    • Installation
      • The process of unpacking and placing the files from a .deb package onto the system. dpkg -i is the command used to install a package.
    • Removal
      • The process of uninstalling a package. dpkg -r removes the package from the system but typically leaves configuration files behind. dpkg -P removes the package and its configuration files.
    • Package Dependencies
      • Packages that are required by another package to function correctly. dpkg does not handle dependencies automatically, so they must be resolved either manually or with a higher-level tool like apt.
    • Package Database
      • A database maintained by dpkg that stores information about all installed packages on the system, such as version, installation status, and file locations.
    • Control Files
      • Metadata files within a .deb package that describe the package’s content, dependencies, description, version, and installation instructions. This includes files like control, postinst, preinst, etc.
    • Status File
      • A file (typically /var/lib/dpkg/status) where dpkg keeps track of installed, partially installed, or removed packages and their associated metadata.
    • Package List
      • A list of all installed packages on the system. You can view it using dpkg -l, which shows the status, name, and version of each installed package.
    • Querying
      • The process of retrieving information about a package. For example, dpkg -s <package> shows the status and metadata of a package, and dpkg -L <package> lists the files installed by the package.
    • Unpacking
      • The extraction of files from a .deb package archive. dpkg unpacks the contents into the appropriate system directories during installation
    • Trigger
      • A mechanism used by dpkg to perform actions after certain package events, such as installing or removing packages. Triggers allow packages to notify the system about changes (e.g., dpkg --configure).
    • Post-installation/Pre-installation Scripts
      • Scripts included in the .deb package that run automatically during the installation or removal process. These are often used to set up or configure the package after it’s installed.
    • Reconfiguration
      • The process of re-running configuration scripts for a package without reinstalling it. This can be done using the dpkg-reconfigure command.
    • Broken Package
      • A package that cannot be installed or has missing dependencies. If a package installation fails due to unmet dependencies, it may leave the system in a “broken” state, which dpkg -C can help identify.
    • Debconf
      • A configuration management system used by Debian packages to prompt users for input during package installation. This system is used alongside dpkg to interactively configure software.
    • Package Integrity
      • Ensuring that a package is not corrupted during installation. dpkg checks package integrity and can refuse to install a package if it is broken or corrupted.
    • Locked State
      • A state that prevents dpkg from running if another instance of dpkg is already running, which helps avoid conflicts in package management.
    • Virtual Package
      • A package that doesn’t contain any files itself but acts as a placeholder for other packages providing similar functionality. These are often used for alternatives (e.g., mail-transport-agent).
    • Local Repository
      • A directory of .deb packages that you can manage and install from, using dpkg to install individual packages directly without needing an internet connection.

How to use dpkg

Installing packages

When installing packages with dkgp its important to understand that dpkg handles .deb files and NOT repositories. These are usually obtained through a website

sudo dpkg -i negtbeans-all.deb

Remove packages

Remove the package vlc but keep the configuration files
sudo dpkg -r vlc

Remove the package vlc AND configuration files
sudo dpkg -P vlc

List all files installed by vlc

dpkg -L vlc

List the content of a .deb file

All contents of negtbeans-all.deb without installing it!
sudo dpkg -c negtbeans-all.deb

List all packages

sudo dpkg --list

Extract content of packages

Extract content of package negtbeans-all.deb without actually installing it or configuring it
sudo dpkg --unpack negtbeans-all.deb

List info of a package

For the package vlc
sudo dpkg -s vlc

Note:This output display similar data as apt show vlc.
This command query the underlying package database at
/var/lib/dpkg/status
. apt does also provide additional data pulled from repositories

Help menu

dpkg --help