[statenjason]

What is Nix?

Nix is a powerful package manager for Linux and other Unix systems that makes package management reliable and reproducible. It provides atomic upgrades and rollbacks, side-by-side installation of multiple versions of a package, multi-user package management and easy setup of build environments.

What is NixOS?

NixOS is a Linux distribution with a unique approach to package and configuration management. Built on top of the Nix package manager, it is completely declarative, makes upgrading systems reliable, and has many other advantages.

[1]: https://nixos.org/

[mehrdadn]

Thanks, but that makes me wonder how that's even possible given that distros make their own modifications? Do people port each distro's packages to Nix then? Are they kept up-to-date? Or does it automatically translate from apt/pacman/etc. databases somehow? Or does it just basically install vanilla packages on all distro?

[throwaway894345]

Yeah, there is a giant repo of package definitions at https://github.com/NixOS/nixpkgs. Those definitions tell nix how to build everything from the ground up.

[tathougies]

> how that's even possible given that distros make their own modifications?

Own modifications to what? All the packages in nixpkgs depend only on other packages in nixpkgs. If you install nix on an ubuntu system and then install a package from nixpkgs, then that package won't use any ubuntu libraries.

[mehrdadn]

> Own modifications to what?

To the packages. e.g. I believe Ubuntu modifies Python so that sudo pip install uses /usr/local instead of /usr. Lots of other patches and backports I'm not necessarily aware of. That's basically what makes Ubuntu Ubuntu, otherwise it'd be more like Arch. So how does Nix deal with this? Do you get the value-add from your distro or do you basically end up with pseudo-Arch wherever you start?

[markandrewj]

The Nix packages are independent of the OS, this is actually one of the advantages of using Nix. It means that similar to when using Python virtual environments user packages are not mixed in with system packages. Nix also versions package changes. When switching between versions, Nix just updates the paths in your environment. If you wanted to stop using the packages all together you only need to remove the environment path.

Another advantage is that you define installs as part of configuration file, similar to Ansible/Chef/ect so things become repeatable.

The difference between Arch and Ubuntu is not so much that patches are applied to packages though, it's that packages are precompiled for Ubuntu, where as packages for Arch are often compiled from source.

Nix can compile packages from source, or use a binary from cache if it is available.

[fwip]

If you install python through nix, you get the nix version.

If you install python through apt, you get the ubuntu version.

[mehrdadn]

I get that part. I'm asking what the Nix version is like. Is it like the Ubuntu version with all the patches and backports and everything, or is it like the Arch (i.e. basically original unmodified) version?

[catern]

Nix packages are typically close to upstream, but low-level packages sometimes have patches to make them more reproducible and deterministic, so that they work better with Nix's efforts for determinism and purely-functional packaging.

Nix packages are created from scratch, not copied from another distro. Nix is typically one of the most up-to-date distros: https://repology.org/

[tathougies]

Ah I see. yes as someone who contributes to nixpkgs, there are patches to use the /nix paths rather than the standard posix layout.

NixOS is not POSIX compliant and does not try to be.

[l3s2d]

Not a Nix user, but my understanding is that it's a standalone package manager with its own repositories. On a non-Nix distro, installing a package with Nix is akin to installing a Python module with pip, instead of the distro's package manager. It would not be managed at all by the distro's package manager. On NixOS, Nix is the distro's package manager.

[mehrdadn]

Thanks, but I already got that much. It doesn't answer my question though. If Ubuntu has made a modification to a package (that's basically the entire point of most distros, otherwise they'd be Arch), should I expect those changes in whatever Nix installs?

It also leaves so many other questions unanswered, like what happens if I install GRUB or a new kernel or something else that's supposed to modify the system globally... but that's secondary.

[ymse]

Nix packages can not modify the system globally, by design. Not even on NixOS. This is why Nix allows unprivileged users to install anything.

When you install a package with Nix, all you are doing is drop a symlink in your ~/.nix-profile pointing to some /nix/store/<unique-identifier> item.

When you build a package with Nix (also does not require root privileges), it happens inside a container that can only write to /nix/store/<unique-identifier>.

The <unique-identifier> is a cryptographic hash based on all the inputs (dependencies) to the package (also /nix/store/<hash> items) as well as the build script.

[mehrdadn]

This is a really good explanation, thank you!

[solarkraft]

NixOS only has nixpkgs modifications, not Ubuntu's, as much as Fedora doesn't have Ubuntu's modifications. My understanding is that packages available for Nix are patched to work within its context, but otherwise kept as original as possible, with optional configuration switches.

[Fnoord]

The documentation [1] mentions the possible configuration flags for a package, including Grub (which is not the default bootloader, btw).

[1] https://nixos.org/learn.html

[catern]

No, you should not expect Ubuntu's modifications in packages installed through Nix.

Things like GRUB or the kernel version are handled at the level of NixOS, because, as you say, they affect the system globally.