Managing Debian Package Dependencies
In a previous post, I talked about building a simple Debian package in Ubuntu, however I did not go into details on how to manage the dependencies that your Debian package might require. In this post I will cover exactly that.
dpkg and Dependencies
Previously we installed our package using the dpkg -i command. However, the problem with dpkg is that by itself, it is not capable of managing repositories. Therefore, higher level tools (such as apt-get) are required to fetch dependencies from repositories.
dkpg is only the core tool that installs/removes/configures packages, taking care of dependencies and other factors. apt-get and aptitude are tools that manage repositories, download data from them, and use dkpg to install/remove packages from them. This means, that apt-get and aptitude can resolve dependencies and get required packages from repository, but dpkg cannot, because it knows nothing about repositories.
Specifying Dependencies
We can specify the required dependencies of our package in our package's control file (located in DEBIAN/control) by listing them as a list of package names separated by commas in the Depends field:
Package: mypackage
Version: 1.0-0
Section: base
Priority: optional
Architecture: all
Depends: erlang-nox, erlang
Maintainer: Andres Alvarez <myemail@gmail.com>
Description: A new and improved C++ Compiler
We can see that the package depends on erlang and erlang-nox. We could also be more specific and specify an exact version of the dependency:
Depends: erlang (>= 1.2)
Additionally, we can use pipe symbols (|) to specify alternative package names, similar to saying “or” in conditional operations:
Depends: erlang-nox | erlang, maven, rrdtool
Installing Dependencies
What we want is to install the package's dependencies the momment we begin to install the package, NOT after it has finished installing (which can be done with apt-get -f install)
Introducing Gdebi
Gdebi is a tool that can install a Debian package along with its dependencies. However in newer versions of Ubuntu it is not installed by default, so you need to install it using apt-get install gdebi-core.
Once installed, we can install our package using the following command:
gdebi install my-package.deb
This will proceed to install to install the package as well as the dependencies listed in the control file.
Unfortuntely for some reason, gdebi does not provide a -y option like apt-get does. This makes it unappropriate for using it inside shell scripts.
Enter apt-get
apt-get is a better choice if you want to install your package with its dependencies from shell scripts, since we can pass the -y option to the install command. Moreover, this approach is more optimal when you set up and use a local apt repository.
Assuming we have added our package to our local apt repository, we can proceed to install it like this:
apt-get install mypackage
apt will search our repository for the package, and once it finds it it will proceed to install the listed dependencies, and then install the package. It is worth mentioning that apt-get install also uses dpkg internally.