NixOS

Resources

• Nix Package Manager Guide
• Distrowatch: NixOS

Introduction

NixOS is a Linux distro that builds on a purely functional package manager: Nix. Nix stores packages at the directory /nix/store as values in a functional programming language. E.g.,

/nix/store/b6gvzjyb2pg0kjfwrjmg1vfhh54ad73z-firefox-33.1/

Where b6gv… is a cryptographic hash of the package’s build dependency graph.

This comes with a couple of advantages:

• You can have multiple versions or variants of a package installed at the same time.
• Nix ensures that that package dependency specifications are complete.
• Upgrading or uninstalling an application cannot break other applications.
• Packages aren’t overwritten, the old versions are still there after an upgrade, so you can roll back.
• Reproducible system configurations.
• Safe to test changes.
• You can build and install your whole distro from basically a config file.

Declarative system configuration model

When installing NixOS, the entire distro (kernel, apps, configs, etc) is built from a configuration file by the Nix package manager. This means that with one command,

nixos-rebuild switch

you can build your whole system on a new machine.

Installing the package manager

The Nix installer creates a single-user installation by default, so to run a multi-user installation we include a daemon that manages the store and with better isolation for local builds,

sudo curl -L https://nixos.org/nix/install | sh -s -- --daemon

Rollback

If you want to undo a nix-env operation there are several nice ways to interact with the package manager,

nix-env --list-generations
nix-env --rollback
nix-env --switch-generation 43

Garbage collection

nix-env operations such as upgrades (-u) and uninstall (-e) never actually delete packages from the system. All they do is to create a new user environment that no longer contains symlinks to the “deleted” packages. To delete non-current generations of your profile,

nix-env --delete-generations old
nix-env --delete-generations 10 11 14

After removing appropriate old generations you can run the garbage collector,

nix-store --gc

There is a command to run all above in one,

nix-collect-garbage -d

Cons with NixOS

• You have to set up the system the Nix way, which is non standard.
• If packages are not available on Nix you will have to get your hands dirty and add it yourself. However, there are a lot of packages on Nix compared to other package managers as can be seen at Repology.
• Lack of documentation.
• It can be difficult to run pre-compiled binaries, since the dependencies are not available at the hard coded locations (e.g., /usr/lib).

Conclusion

After trying out Nix, I think that the package manager is interesting and it’s great that you can specify and build your entire system from it. The reproducibility is fantastic. However, the flexibility in using the system with other packages, binaries, etc, is not very good.