Rebuilding and Modifying Debian Packages

Introduction

Debian's package management system is key to software administration on Debian and its derivatives (like Ubuntu). It simplifies installing, updating, and removing software. However, pre-built packages might not always meet specific user or organizational needs – perhaps a patched version, extra features, or performance tweaks are required. This guide details rebuilding and modifying existing Debian packages to precisely match your requirements.

Understanding Debian Packages (.deb files)

Debian packages are archives containing compiled binaries, configuration files, and installation scripts. Their internal structure is crucial to understand:

• DEBIAN directory: Contains control files managing package installation, upgrades, and removal.
• Data archive: Holds the package's actual files.

Key Files Within a Debian Package:

• control: Specifies package dependencies and metadata (version, maintainer, description).
• changelog: Logs all package changes.
• rules: Defines how the package is built from source.

Essential Debian Packaging Tools:

• dpkg: The core tool for package installation and removal.
• APT (Advanced Package Tool): A higher-level tool for retrieving and installing packages from repositories.
• dpkg-dev: A suite of tools for building Debian packages.

Reasons for Modifying Debian Packages

Customizing software optimizes efficiency, enhances security, and allows adding or modifying features for a specific environment. Common reasons include:

• Customization: Tailoring software to local policies or performance needs.
• Security Patches: Applying security fixes not yet in official releases.
• Functional Updates: Adding features absent from the standard package.

Preparing Your Environment

1. Install Necessary Tools:

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

2. Create a Working Directory:

mkdir ~/packaging
cd ~/packaging

3. Obtain the Source Package:

Download the source code using:

apt-get source package-name

This downloads the .dsc (description file), the original tarball (.tar.gz), and potentially a .diff.gz file (showing Debian's changes to the original source).

Modifying the Package

1. Unpack the Source:

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

2. Navigate the Source Tree:

The unpacked directory contains the original source and a debian directory (holding packaging scripts and control files).

3. Make Your Changes:

Modify the source code directly or apply patches using tools like quilt. Debian's patch system efficiently manages multiple patches.

Updating Package Metadata

1. Update the Changelog:

mkdir ~/packaging
cd ~/packaging

This opens an editor to add a new changelog entry, tracking versions and changes.

2. Adjust Control File and Metadata:

Modify the control file to change dependencies, priority, section, etc.

Rebuilding the Package

Rebuild the package using:

apt-get source package-name

This builds the package (including your changes), omitting the signing step. It handles dependencies and ensures correct compilation.

Testing and Deployment

1. Install the Rebuilt Package:

Test the package by installing it:

dpkg-source -x package-name_version.dsc

Verify correct installation and functionality.

2. Ongoing Maintenance:

Maintain your custom package by incorporating upstream changes. Regularly update the source and rebase your modifications to prevent conflicts and maintain security.

Conclusion

Rebuilding and modifying Debian packages is a valuable skill for flexible and secure software management in Debian-based environments. This allows precise tailoring of software to meet specific needs.

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