# Debian building packages

Debian packages (`.deb`) are the standard distribution format. Building custom packages requires source and metadata.

## Package components

A source package consists of three files:

- `.orig.tar.gz`: original upstream source
- `.debian.tar.gz` or `.diff.gz`: Debian-specific patches and metadata
- `.dsc`: metadata file (dependencies, checksums)

Example:

```
hello_2.10-1.orig.tar.gz
hello_2.10-1.debian.tar.gz
hello_2.10-1.dsc
```

## Extracting source

Extract source package:

```bash
dpkg-source -x hello_2.10-1.dsc
cd hello_2.10-1
```

This unpacks upstream source and applies Debian patches.

## Building

Install build dependencies:

```bash
cd hello_2.10-1
sudo apt build-dep .
```

Build package:

```bash
debuild              # builds, signs, creates .deb
debuild -us -uc      # builds, no GPG signing
dpkg-buildpackage    # lower-level alternative
```

Output: `.deb` file in parent directory.

## Installing custom package

Install locally-built package:

```bash
sudo dpkg -i hello_2.10-1_amd64.deb
sudo apt install ./hello_2.10-1_amd64.deb     # also resolves dependencies
```

## Creating from scratch

Create simple `debian/` directory structure:

```
source/
├── debian/
│   ├── control        # package metadata
│   ├── rules          # build instructions
│   ├── changelog      # version history
│   └── copyright      # license info
└── main.c
```

Minimal `debian/control`:

```
Source: myapp
Maintainer: Your Name <you@example.com>
Section: utils
Priority: optional
Build-Depends: debhelper-compat (= 13)
Standards-Version: 4.6.0

Package: myapp
Architecture: any
Depends: ${shlibs:Depends}
Description: My Application
 A brief description.
```

Minimal `debian/rules`:

```makefile
#!/usr/bin/make -f
%:
	dh $@
```

Then build:

```bash
debuild -us -uc
```

## Contributing to Debian

To formally contribute:
1. Check existing packages
2. Understand Debian Policy
3. Create quality package
4. Find sponsor (established developer)
5. Submit patch or new package
6. Go through review process

See [Debian New Maintainers Guide](https://www.debian.org/doc/manuals/maint-guide/).

## Key files

- `debian/control`: package metadata, dependencies
- `debian/rules`: build rules (often just `dh $@`)
- `debian/changelog`: version history (mandatory format)
- `debian/copyright`: license and copyright info
- `debian/install`: files to install
- `debian/systemd/`: systemd units

## Tips

- Always check copyright and licensing
- Test package install/removal thoroughly
- Use `debhelper` (`dh`) to simplify `debian/rules`
- Never hardcode paths; use `/usr/bin`, not `/opt/bin`
- Clean source tree: `debclean` or `debuild clean`
- Linting: `lintian package.deb` checks for common issues

Building quality packages requires testing and knowledge of Debian conventions.