Debian Packages

As an example, I will be using a very simple script that prints the Wireless SSID the server is connected to and it’s Signal Strength. The goal is to log this information and read it with journalctl

The script, signalstrengthd.sh looks like this:

#!/bin/bash
# a loop that checks wifi status every 10 seconds
while true; do
    awk 'BEGIN{printf strftime("%d/%m/%Y %H:%M:%S UTC -- ", systime())}'
    echo -n $(networkctl status vwsta -n0 | grep -i "Wifi access point")
    awk 'NR==3 {print " | WiFi Signal Strength = " $3 "00 %"}' /proc/net/wireless 
    sleep 10
done

There are two types of packages: source & binary.

Source Packages

`.dsc`

Built from the original source code. A source package that provides us with all the necessary files to compile or otherwise build the desired piece of software. Requires 3 files:

Original Source (xxx.orig.tar.xz)
Debian Source (xxx.debain.tar.xz)
Source Control (dsc)

Binary Packages

`.deb`

Binary packages use a DEBIAN directory

Consists of the following:

debian-binary
- version of the deb file format
- control.tar.gz
- metadata about the package
data.tar.gz
- data files of the package

Required Files

mkdir -p debian/source

touch debian/changelog
touch debian/compat
touch debian/control
touch debian/rules
touch /debian/source/format

1. `rules` - instructions for debhelper

Makefile that is used in the build process.
According to this, the required targets are:
- clean
- build
- build-arch
- build-indep
- binary
- binary-arch
- binary-indep

If you do this, it will pass to the included Makefile:

DH_VERBOSE = 1
#!/usr/bin/make -f  
# % sign means any target
%:  
# calls a single program, dh, with the target name
# dh is a wrapper script that runs appropriate sequences of dh_*
  dh $@

2. `control` - package specific information

Metadata that has at least 2 sections - one for source and one for binary.

Key Value Pairs grouped into sections.

Mandatory Fields include:

Source
Maintainer
Standards-Version
Package
Architecture
Description

Highly Recommended:

Priority
Section

3. `compat` - compatibility level for debhelper

4. `changelog` - changes to the package and software

Metadata explaining the changes of the package, in a very rigid format. It sets the name, version, and distribution of the package.

If distribution name = UNRELEASED, then the package build is not targeted for a particular distribution and does not need to be signed.

Leaving this empty will precent the package from building.

Best practice is to use dch (debchange)

5. format

I’ve really only seen/used a format file with this format specified: 3.0 (quilt)

This means that we can expect three files:

original source
debian source
source control

For anything >= 2.0, the default compression is xz. For 1.0, default compression is gzip (gz).

Not Required Files But Excellent Files Nonetheless

preinst
- Runs before installation
postinst
- Runs after installation

Build

Build With `dpkg` suite

https://metebalci.com/blog/a-minimum-complete-example-of-debian-packaging-and-launchpad-ppa-hellodeb/

dpkg comes standard on Ubuntu, and contains various tools. We will be using 2 in particular:

dpkg-deb

Builds a binary package. a low-level tool that you should not call by itself (we'll use it in the rules file though), it is what is responsible for actually creating the .deb file.

dpkg-buildpackage

A Perl Script. Can also run various steps, like running `dpkg-source`

Using the flag –build provides these options:

source
any
all
binary
full

We will also need to install dpkg-dev to generate packages.

dpkg-dev

```bash sudo apt install dpkg-dev ```

Folder Structure

Run dpkg-buildpackage in the directory with the source code, which should also contain a directory debian with the files mentioned above included. The .deb output will be in the parent directory of where dpkg-buildpackage is run.

Build!

Assuming you have everything from the list of required files, you can build the package. If you run dpkg-buildpackage by itself, it will run by default dpkg-buildpackage --build full. The build option that you provide corresponds to what you need to have in your debian/rules file. Here are the --build options you have with dpkg-buildpackage, and the targets that are run from the rules file:

full
- clean, build, binary
- full also builds the source packages, while binary does not
all
- clean, build-indep, binary-indep
any
- clean, build-arch, binary-arch
binary
- clean, build, binary
source
- clean

dpkg-buildpackage

Need to add completed rules file that builds the tarball…

Buld With `debmake`

According to this site, debmake is currently Broken :/

https://wiki.debian.org/SimplePackagingTutorial

Build With `dh-make`, `debuild`, and a bash script

Using dh-make, creating a package can be pretty straight forward. Using this script for our example should be everything we need to create a debian package for the signal strength checker.

dh-make – To prepare the package debuild – To build the package

#!/bin/bash

# Set the variables that will be used by dh_make
export DEBEMAIL=""
export DEBFULLNAME="First Last"

mkdir -p signal_strength_pkg/signalstrengthd-0.1
cd signal_strength_pkg/signalstrengthd-0.1

cat>signalstrengthd.sh << EOF 
#!/bin/bash
# a loop that checks wifi status every 10 seconds
while true; do
    awk 'BEGIN{printf strftime("%d/%m/%Y %H:%M:%S UTC -- ", systime())}'
    echo -n $(networkctl status vwsta -n0 | grep -i "Wifi access point")
    awk 'NR==3 {print " | WiFi Signal Strength = " $3 "00 %"}' /proc/net/wireless 
    sleep 10
done
EOF

cat>signalstrengthd.service << EOF
[Unit]
Description=Wifi Signal Strength Logger

[Service]
Type=simple
User=root
ExecStart=/usr/local/bin/signal-strength.sh

[Install]
WantedBy=multi-user.target
EOF

chmod +x signal-strength.sh

dh_make --indep --createorig 
# dh_make --createorig -e email@email.com -i -y

cd debian

rm *.ex *.EX
rm README.*

echo "signalstrengthd.sh /usr/local/bin/" > install
echo "signalstrengthd.service /usr/lib/systemd/system/" >> install

# Create .postinst
cat>postinst << EOF
#!/bin/bash
set -e
/usr/bin/systemctl daemon-reload
/usr/bin/systemctl enable signalstrengthd.service
exit 0
EOF

# Build Package
debuild -us -uc
# if this fails, you may need to rebuild the original tar
# dh_make --createorig

cd ..

sudo apt install ./signalstrengthd-0.1.deb

- `debuild` -

when running debuild -us -uc, -us -uc tells the script not to sign the .dsc and .changes files accordingly. This is pretty much the standard run.

You can also fancy it up more with: debuild -us -uc -i -I -b -i and -I makes the script ignore common version control files. -b tells debuild to only create binary packages

Making Changes

If you make a change, like renaming a file, and try to run debuild again, you will get an error like so:

dpkg-source: info: local changes detected, the modified files are:
 signalstrengthd-1.5/services/signalstrengthd-log.service
dpkg-source: error: aborting due to unexpected upstream changes, see /tmp/signalstrengthd_1.5-1.diff.JrsnWU
dpkg-source: info: you can integrate the local changes with dpkg-source --commit

If you run waht it suggests, dpkg-source --commit, you will create a patch. You can then run debuild again successfully.

Build Debian Package with `pbuilder` and a bash script

https://blog.packagecloud.io/building-debian-and-ubuntu-packages-with-pbuilder/

Debian Packages

Source Packages

.dsc

Binary Packages

.deb

Required Files

1. rules - instructions for debhelper

2. control - package specific information

3. compat - compatibility level for debhelper

4. changelog - changes to the package and software