[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/

[mehrdadn]

Okay thanks, so it sounds like I'll (roughly) end up with Arch (i.e. mostly-unmodified) whether I start on Ubuntu, Fedora, or whatever. I have another on that front: what about things like kernels? Don't those conflict with the OS?

[thequux]

If you install the "linux" package using nix on Debian, you get a directory in your nix store (the collection of "installed" packages) containing a bzImage, a System.map, and a `lib` directory containing all of the kernel modules. It would then be up to you to build an initrd and wire it into your bootloader, if that's what you wanted to do.

In other words, Nix packages are just files in their own special place on the disk (under /nix). If you want to configure binaries from those packages to run as daemons, or otherwise be wired into the system globally, that's up to you.

In fact, this is also true for the packages that you've "installed"! The nix package manager creates a package that represents your "user environment", and that package just merges all of the packages you installed using symlinks, and a symlink to that package is added to your $PATH.

[dataflow]

"Just files" doesn't quite capture the complexity of the situation to me though. Say I happen to install package X via apt and Y via nix, and both of them depend on Z (in apt and nix respectively), and Z needs to bind to a port, then I imagine both will install but one of them will break, possibly including their dependents. Or if I install a package on Nix that expects a certain syscall that's not in the Ubuntu kernel yet (maybe like the recent /usr/bin/sleep issue with WSL), then that either breaks Nix or my ability to keep using an Ubuntu kernel. Right? And there are probably other things I'm just lacking the imagination for right now. But it seems to me there are all sorts of conflicts that can come up in practice. I've seen enough trainwrecks when upgrading even across OS versions that I have a hard time seeing how running 2 package managers can work on a single OS without breaking something?

[catern]

Those are handled by NixOS - that's the purpose of NixOS, it was built on top of Nix explicitly to manage such things. You can read some about NixOS at https://nixos.org/nixos/about.html

[geofft]

And in particular, NixOS is a full OS, like Arch/Ubuntu/etc. You can't install NixOS side-by-side with Arch any more than you can install Arch side-by-side with Ubuntu. Nix-sans-NixOS is only the stuff that can be installed side-by-side with an existing OS - no service management, no kernels, etc.

[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.