Install Nix on Arch

Why this matters

You already have Nix 2.35.2 running. This lesson is about knowing what is on your disk, so that when a tutorial says "edit nix.conf" or "the installer did X", you can check whether that applies to your machine. It often does not, because you did not use the installer most tutorials assume.

Concept

What you actually installed

Your Nix came from the Arch package, not from an installer script:

pacman -Qo /usr/bin/nix

/usr/bin/nix is owned by nix 2.35.2-2

This matters. The Arch package and the Determinate installer lay things out differently:

If a guide tells you to add /nix/var/nix/profiles/default/bin to PATH, skip it. That directory does not exist on your machine.

The daemon

Nix runs a daemon as root. Your user talks to it over a socket; the daemon does the actual builds as unprivileged nixbld users and writes to /nix/store. That is why /nix/store is owned by root:nixbld and you cannot write to it directly.

systemctl is-active nix-daemon

active

Config: two files

System config is /etc/nix/nix.conf. Yours is almost empty:

build-users-group = nixbld

User config is ~/.config/nix/nix.conf. This is where flakes were turned on:

experimental-features = nix-command flakes

The merged result is what nix config show prints. fetch-tree appears there too because flakes implies it.

Verify: cat ~/.config/nix/nix.conf. Yours currently contains that line twice. Harmless, but delete one.

The fish PATH

Your user profile lives at ~/.local/state/nix/profiles/profile, symlinked from ~/.nix-profile. Packages installed with nix profile add land in ~/.nix-profile/bin. Your config.fish already adds it:

fish_add_path $HOME/.nix-profile/bin

Nothing more is needed for the Arch package. The nix binary itself is in /usr/bin.

The Determinate installer, for reference

On a machine without an Arch package (Ubuntu, macOS, WSL), the common route is:

curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | sh -s -- install

Verify: curl -sL https://install.determinate.systems/nix | head -40. At time of writing the script pins nix-installer v3.22.5. It enables flakes for you and sets up the daemon. Do not run this on your Arch machine; you would get two Nix installs fighting over /nix.

Trusted users

nix config show reports trusted-users = root. You are not a trusted user. Consequence: a flake's nixConfig.extra-substituters (binary caches) is ignored for you unless you add trusted-users = root dave to /etc/nix/nix.conf. You will hit this when a project uses Cachix. Not needed today.

Uninstalling

Shown as text. Do not run it now.

sudo systemctl disable --now nix-daemon
sudo pacman -Rns nix
sudo rm -rf /nix
rm -rf ~/.nix-profile ~/.local/state/nix ~/.cache/nix ~/.config/nix

Remove the fish_add_path line from config.fish and the nixbld users the package created (getent passwd | grep nixbld).

Try it

Confirm the layout described above matches your disk.

ls -la ~/.nix-profile
ls /nix/var/nix/profiles/

lrwxrwxrwx 1 dave dave 44 Jun 16 14:38 /home/dave/.nix-profile -> /home/dave/.local/state/nix/profiles/profile
per-user

No default entry. That is the Arch layout.

Exercise

A tutorial says: "If nix is not found after install, run . /nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh." Decide whether that applies to you and say why.

Trap

Running the Determinate installer "to be safe" on top of the Arch package. Both want to own /nix, /etc/nix/nix.conf and nix-daemon.service. You get a broken daemon and two binaries. One install method per machine. Yours is pacman.

Checkpoint