Sometimes, things just don't work on NixOS. For example, say a developer has written a program that uses the an executable in the directory /usr/bin/someExecutable. Unfortunately, say this developer also hardcoded this directory path in their code. This means that we cannot change it, or patch it using normal means (such as creating a wrapper for it).

In order to bypass this, we can create a sandbox in NixOS that uses the Unix "Filesystem Hierarchy Standard" (FHS¹).

There are two methods of using the FHS:

You can declare a FHS environment in your configuration.nix file. This allows you to enter this sandboxed environment using a command in any directory. This is done by using the pkgs.buildFHSUserEnv function to create a sandbox derivation.

In this example, we use pkgs.buildFHSUserEnv to create a sandbox to aid in C++ development for other Linux systems. We include various debugging tools, such as gdb and valgrind, as well as the required libraries that we'll need, such as llvm.

environment.systemPackages = with pkgs; [
    (pkgs.buildFHSUserEnv {
        name = "cppfhs";
        runScript = "bash";
        targetPkgs = pkgs: with pkgs; [
            clang_8 gdb llvm_8 valgrind
        ]; 
    })
];

We name this derivation cppfhs, which allows us to use the following command in any shell to quickly enter this environment:

$ cppfhs