What is Nix?

Programming Language

  • Dynamically typed - Similar semantics to JavaScript and Lisp.

  • Functional programming - Higher order functions, immutability, etc.

  • Lazy - Values are not evaluated until needed.

Package Manager

  • Packages as special Nix objects that produce derivations and build artifacts.

  • One package can serve as build input of another package.

  • Multiple versions of the "same" package can be present on the same system.

Build System

  • Packages are built from source code.

  • Build artifacts of packages are cached based on content address (SHA256 checksum).

  • Multi language / multi repository build system.

    • Language agnostic.
    • Construct your own build system pipeline.

Operating System

  • Nix itself is a pseudo operating system.

    • Rich set of Nix packages that can typically be found in OS packages.

  • Nix packages can co-exist non-destructively with native OS packages.

    • All Nix artifacts are stored in /nix.

    • Global "installation" is merely a set of symlinks to Nix artifacts in /nix/store.

  • Lightweight activation of global Nix packages.

    • Add ~/.nix-profile/bin/ to $PATH.

    • Call source ~/.nix-profile/etc/profile.d/nix.sh to activate Nix.

    • Otherwise Nix is almost invisible to users if it is not activated.

  • NixOS is a full Linux operating system.

Reproducibility

  • Key differentiation of Nix as compared to other solutions.

  • Nix packages are built inside a lightweight sandbox.

    • No containerization.

    • Sanitize all environment variables.

    • Special $HOME directory at /homeless-shelter.

    • Reset date to Unix time 0.

    • Very difficult to accidentally escape the sandbox.

  • Content-addressable storage.

    • Addresses of Nix packages are based on a checksum of the source code, plus other factors such as CPU architecture and operating system.

    • If the checksum of the source code changes, the addresses of the derivation and any build artifacts also change.

    • If the address of a dependency changes, the addresses of the derivation and build artifact also change.