How to install nix

nain4 is distributed and its dependencies are managed using nix. The reasons for this are explained in why nix?.

On your personal computer

In order to install nix on your personal computer, simply use1

curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | sh -s -- install

The installer will guide you through the installation steps. This installer requires super-user permissions (sudo).

On a HPC cluster

The situation on HPC clusters is different, as we usually we don't have super-user permissions. At the moment the installation of nix in this kind of environments is not fully supported. In the meantime, you may want to check How to make nain4 available in a Geant4/cmake project

direnv

We strongly recommend using direnv to automatically activate and deactivate development environments when entering or leaving a project directory.

To use direnv:

  1. Make sure that it is installed on your system. To install direnv with nix, run

    nix profile install nixpkgs#direnv

  2. Don't forget to hook it into your shell. Depending on which shell you are using, this will involve adding one of the following lines to the end of your shell configuration file:

    eval "$(direnv hook bash)"  # in ~/.bashrc
eval "$(direnv hook zsh)"   # in ~/.zshrc
eval `direnv hook tcsh`     # in ~/.cshrc

The first time direnv wants to perform an automatic switch in a new context (combination of directory + .envrc contents), it asks you for permission to do so. You can give it permission by typing direnv allow in the shell. The message that direnv gives you at this stage is pretty clear, but it's usually written in red, thus you might get the mistaken impression that there is an error.

Now, every time you enter the directory you will see a message like:

direnv: loading .envrc
direnv export: +FOO +BAR +BAZ ...

and when you exit

direnv: unloading