Introduction

The Debian packaging system is an integral part of managing software on Debian and its derivatives like Ubuntu. It facilitates the installation, upgrade, and removal of software packages. Sometimes, however, the available binary packages may not meet all the specific requirements of a user or organization, be it due to the need for a patched version, additional features, or customization for performance optimizations. This article delves deep into the process of rebuilding and modifying existing Debian packages, offering a guide for those who need to tailor software packages to their precise requirements.

Understanding Debian Packages

Debian packages, with the .deb file extension, are archives that contain compiled binaries, configuration files, and installation scripts. Understanding the internal structure of these packages is critical. A typical .deb package includes:

• DEBIAN directory: Holds control files that manage how the package is installed, upgraded, or removed.
• data archive: Contains the actual files of the package.

Common Files in a Debian Package

• control: Details package dependencies and metadata like version, maintainer, and description.
• changelog: Records all the changes made to the package.
• rules: Specifies how the package is to be built from its source.

Debian Packaging Tools

• dpkg: The base tool that handles package installation and removal.
• APT (Advanced Package Tool): Works at a higher level to handle the retrieval and installation of packages from remote repositories.
• dpkg-dev: A collection of tools necessary to build Debian packages.

Why Modify a Debian Package?

Customizing software can optimize operational efficiency, enhance security, and add or modify features to suit better the unique environment in which they operate. Typical reasons for modifying packages include:

• Customization: Adjusting software to fit specific local policies or performance requirements.
• Security patches: Quickly applying security patches that are not yet part of official releases.
• Functional updates: Adding features not available in the standard package.

Preparing the Environment

Installing Necessary Tools

Before beginning, ensure your system has the tools required for Debian package development installed:

sudo apt-get install dpkg-dev devscripts build-essential fakeroot

Setting Up a Working Directory

It is advisable to work in a clean directory to avoid contamination of the build environment:

mkdir ~/packaging cd ~/packaging

Retrieving the Source Package

To modify a package, first, download the source code:

apt-get source package-name

This command downloads several files, including the .dsc (description file), the original tarball (.tar.gz), and possibly a diff file (.diff.gz), which details changes made by Debian maintainers to the original source.

Modifying the Package

Unpacking the Source Package

After downloading, unpack the source:

dpkg-source -x package-name_version.dsc

Navigating the Debian Package Source Tree

The unpacked source directory will typically contain the original source and a debian directory where all packaging scripts and controls are located.

Editing Files

Changes can be made directly to the source or through patches using tools like quilt. Debian's patch management system allows multiple patches to be applied and tracked effectively.

Updating the Debian Package Metadata

Modifying the Changelog

It's crucial to update the changelog file:

dch -i

This command opens an editor to add a new entry, helping to track package versions and changes systematically.

Adjusting the Control File and Other Metadata

Other modifications may include tweaking the control file to change dependencies or other metadata like priority and section.

Rebuilding the Package

To rebuild the package, use:

debuild -us -uc

This command builds the package along with its changes, skipping the signing process. It handles dependency resolution and ensures that the package compiles correctly on your system.

Testing and Deployment

Installing the Rebuilt Package

Test the newly built package by installing it:

sudo dpkg -i ../package-name_version_arch.deb

Testing ensures that the package installs correctly and functions as expected.

Maintaining the Package

Maintaining a custom package involves keeping abreast of upstream changes and integrating them as necessary. Regularly updating the source and rebasing your changes can prevent conflicts and keep the software secure.

Conclusion

Rebuilding and modifying Debian packages is a powerful skill that can greatly enhance the flexibility and security of software management in a Debian-based environment. By mastering this craft, users and organizations can ensure that their software systems are perfectly tailored to meet their unique demands.