Configuration Files

repo2docker looks for configuration files in the repository being built to determine how to build it. In general, repo2docker uses the same configuration files as other software installation tools, rather than creating new custom configuration files.

A number of repo2docker configuration files can be combined to compose more complex setups.

The binder examples organization on GitHub contains a list of sample repositories for common configurations that repo2docker can build with various configuration files such as Python and R installation in a repository.

Below is a list of supported configuration files (roughly in the order of build priority):

environment.yml - Install a Python environment

environment.yml is the standard configuration file used by conda that lets you install any kind of package, including Python, R, and C/C++ packages. repo2docker does not use environment.yml to create and activate a new conda environment. Rather, it updates a base conda environment with the packages listed in environment.yml. This means that the environment will always have the same default name, not the name specified in environment.yml.


You can install files from pip in your environment.yml as well. For example, see the binder-examples environment.yml file.

You can also specify which Python version to install in your built environment with environment.yml. By default, repo2docker installs Python 3.7 with your environment.yml unless you include the version of Python in this file. conda supports all versions of Python, though repo2docker support is best with Python 3.7, 3.6, 3.5 and 2.7.


If you include a Python version in a runtime.txt file in addition to your environment.yml, your runtime.txt will be ignored.

requirements.txt - Install a Python environment

This specifies a list of Python packages that should be installed in your environment. Our requirements.txt example on GitHub shows a typical requirements file. - Install Python packages

To install your repository like a Python package, you may include a file. repo2docker installs files by running pip install -e ..

Project.toml - Install a Julia environment

A Project.toml (or JuliaProject.toml) file can specify both the version of Julia to be used and a list of Julia packages to be installed. If a Manifest.toml is present, it will determine the exact versions of the Julia packages that are installed.

REQUIRE - Install a Julia environment (legacy)

A REQUIRE file can specify both the version of Julia to be used and which Julia packages should be used. The use of REQUIRE is only recommended for pre 1.0 Julia versions. The recommended way of installing a Julia environment that uses Julia 1.0 or newer is to use a Project.toml file. If both a REQUIRE and a Project.toml file are detected, the REQUIRE file is ignored. To see an example of a Julia repository with REQUIRE and environment.yml, visit binder-examples/julia-python.

install.R - Install an R/RStudio environment

This is used to install R libraries pinned to a specific snapshot on MRAN. To set the date of the snapshot add a runtime.txt. For an example install.R file, visit our example install.R file.

apt.txt - Install packages with apt-get

A list of Debian packages that should be installed. The base image used is usually the latest released version of Ubuntu.

We use apt.txt, for example, to install LaTeX in our example apt.txt for LaTeX.

DESCRIPTION - Install an R package

To install your repository like an R package, you may include a DESCRIPTION file. repo2docker installs the package and dependencies from the DESCRIPTION by running devtools:install_git(".").

You also need to have a runtime.txt file that is formatted as r-<YYYY>-<MM>-<DD>, where YYYY-MM-DD is a snapshot of MRAN that will be used for your R installation.

manifest.xml - Install Stencila

Stencila is an open source office suite for reproducible research. It is powered by the open file format Dar.

If your repository contains a Stencila document, repo2docker detects it based on the file manifest.xml. The required execution contexts are extracted from a Dar article (i.e. files named *.jats.xml).

You may also have a runtime.txt and/or an install.R to manually configure your R installation.

To see example repositories, visit our Stencila with R and Stencila with Python examples.

postBuild - Run code after installing the environment

A script that can contain arbitrary commands to be run after the whole repository has been built. If you want this to be a shell script, make sure the first line is #!/bin/bash.

An example use-case of postBuild file is JupyterLab’s demo on It uses a postBuild file in a folder called binder to prepare their demo for binder.

start - Run code before the user sessions starts

A script that can contain simple commands to be run at runtime (as an ENTRYPOINT to the docker container). If you want this to be a shell script, make sure the first line is #!/bin/bash. The last line must be exec "$@" or equivalent.

Use this to set environment variables that software installed in your container expects to be set. This script is executed each time your binder is started and should at most take a few seconds to run.

If you only need to run things once during the build phase use postBuild - Run code after installing the environment.

runtime.txt - Specifying runtimes

Sometimes you want to specify the version of the runtime (e.g. the version of Python or R), but the environment specification format don’t let you specify this information (e.g. requirements.txt or install.R). For these cases, we have a special file, runtime.txt.


runtime.txt is only supported when used with environment specifications that do not already support specifying the runtime (e.g. when using environment.yml for conda or Project.toml for Julia, runtime.txt will be ignored).

To use python-2.7: add python-2.7 in runtime.txt file. The repository will run in an env with Python 2 installed. To see a full example repository, visit our Python2 example.

repo2docker uses R libraries pinned to a specific snapshot on MRAN. You need to have a runtime.txt file that is formatted as r-<YYYY>-<MM>-<DD>, where YYYY-MM-DD is a snapshot at MRAN that will be used for installing libraries.

To see an example R repository, visit our R example in binder-examples.

default.nix - the nix package manager

Specify packages to be installed by the nix package manager. When you use this config file all other configuration files (like requirements.txt) that specify packages are ignored. When using nix you have to specify all packages and dependencies explicitly, including the Jupyter notebook package that repo2docker expects to be installed. If you do not install Jupyter explicitly repo2docker will no be able to start your container.

nix-shell is used to evaluate a nix expression written in a default.nix file. Make sure to pin your nixpkgs to produce a reproducible environment.

To see an example repository visit nix binder example.

Dockerfile - Advanced environments

In the majority of cases, providing your own Dockerfile is not necessary as the base images provide core functionality, compact image sizes, and efficient builds. We recommend trying the other configuration files before deciding to use your own Dockerfile.

With Dockerfiles, a regular Docker build will be performed.


If a Dockerfile is present, all other configuration files will be ignored.

See the Advanced Binder Documentation for best-practices with Dockerfiles.