recursive-nix example fails to build

[fricklerhandwerk]

Problem

Using Nix 2.21.0 on the only example in the manual fails to build:

nix/src/libutil/experimental-features.cc

Lines 124 to 136 in 478c053

	with import <nixpkgs> {};
	runCommand "foo"
	{
	buildInputs = [ nix jq ];
	NIX_PATH = "nixpkgs=${<nixpkgs>}";
	}
	''
	hello=$(nix-build -E '(import <nixpkgs> {}).hello.overrideDerivation (args: { name = "recursive-hello"; })')
	mkdir -p $out/bin
	ln -s $hello/bin/hello $out/bin/hello
	''

nix-build recursive.nix -I nixpkgs=channel:nixpkgs-unstable --extra-experimental-features recursive-nix

building '/nix/store/mjq5z8z7rp04avbjya9qlfc3xhimnlyz-foo.drv'...
error: creating directory '/nix/var': Permission denied
error: builder for '/nix/store/mjq5z8z7rp04avbjya9qlfc3xhimnlyz-foo.drv' failed with exit code 1;

Proposal

Document everything required to make it work, as done in a Nixpkgs test.

Related:

• A very restricted recursive nix socket in the sandbox #8602
• Make Nix configure itself better when it runs in the sandbox #8698

Checklist

• checked latest Nix manual (source)
• checked open documentation issues and pull requests for possible duplicates

Priorities

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