nixos/multipath: etc_prefix not configured correctly

[bzadm]

Nixpkgs version

• Stable (24.11)

Describe the bug

The multipath module uses the package with the default etc_prefix build option. This means the module will fail to start the service when activated on an empty system because it tries to write into the nix store, relative to the build dir ({nix path}/etc/multipath).

This should be fixed either with the module or the package. A temporary fix is to use a package override, to let the module use /etc/multipath:

  # the fibrechannel cards are setup in a multipath config, we run ZFS on top so some adjustement is required
  services.multipath = {
    enable = true;
    package = pkgs.multipath-tools.overrideAttrs (
      _finalAttrs: previousAttrs: {
        # multipathd wants to write it's binding into $(prefix)/etc
        # the nixpkgs package sets $(prefix)=$out, which leads to the daemon trying to write into the store
        # this adjustement makes it write to /etc/multipath.d at runtime
        makeFlags = previousAttrs.makeFlags ++ [ "etc_prefix=/" ];
      }
    );
  };

Steps to reproduce

Set services.multipath.enable = true; on a system with eligible hardware, it will try to write bindings etc. to the nix store. I only tested (or rather can test) with FibreChannel cards.

Expected behaviour

Write to /etc or a similiar directory.

Screenshots

No response

Relevant log output

Additional context

No response

System metadata

• system: "x86_64-linux"
• host os: Linux 6.12.13, NixOS, 24.11 (Vicuna), 24.11.20250224.3133e42
• multi-user?: no
• sandbox: yes
• version: nix-env (Nix) 2.24.12
• nixpkgs: not found

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