How it works...

Dependencies come from various sources. First, you have the core dependencies of Odoo, the Python interpreter that is used to run the source code, and the PostgreSQL database server used to store the instance data. Git is used for source code versioning and getting the source code of Odoo itself.

Versions of Odoo prior to 11.0 ran with Python 2.7. Starting with Odoo 11.0, the minimum supported version of Python is 3.5. These two versions of Python are not compatible, so a module running on Python 2.7 (with Odoo 9.0 or 10.0, for instance) will require both porting to the specifics of Odoo 11.0 and porting to Python 3. 

Since we will need to edit some files as root or as postgres (the PostgreSQL administrative user) on our server, we need to install a console-based text editor. We suggest nano as it is very simple to use, but feel free to choose any editor with which you feel at ease as long as it works on the console, such as vim, e3, or emacs-nox.

Wkhtmltopdf is a runtime dependency of Odoo used to produce PDF reports. The version required by Odoo 11.0 is 0.12.4, which is not included in the current GNU/Linux distributions. Fortunately for us, the maintainers of wkhtmltopdf provide pre-built packages for various distributions on http://wkhtmltopdf.org/downloads.html.

There are lots of other runtime dependencies that are Python modules, which we can install using pip3 in a virtual environment. However, some of these Python modules can feature some dependencies on native C libraries, for which the Python bindings need to be compiled. Therefore, we install the development packages for these C libraries as well as the Python development package and a C compiler. Once these build dependencies are installed, we can use pip3 install -r requirements.txt (a file that comes from the Odoo source code distribution) to download, compile, and install the Python modules.