Step 3/5 : RUN su aur &&     curl https://nixos.org/nix/install | sh
 ---> Running in 4f0e2c58c30a
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  2399  100  2399    0     0   2825      0 --:--:-- --:--:-- --:--:--  2822
downloading Nix 2.3.1 binary tarball for x86_64-linux from 'https://nixos.org/releases/nix/nix-2.3.1/nix-2.3.1-x86_64-linux.tar.xz' to '/tmp/nix-binary-tarball-unpack.oHgYINQfck'...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 15.2M  100 15.2M    0     0  1951k      0  0:00:07  0:00:07 --:--:-- 2614k
warning: installing Nix as root is not supported by this script!
performing a single-user installation of Nix...
copying Nix to /nix/store................................
installing 'nix-2.3.1'
error: all build users are currently in use; consider creating additional users and adding them to the 'nixbld' group
/tmp/nix-binary-tarball-unpack.oHgYINQfck/unpack/nix-2.3.1-x86_64-linux/install: unable to install Nix into your default profile
The command '/bin/sh -c su aur &&     curl https://nixos.org/nix/install | sh' returned a non-zero code: 1