A great 2016 blog post described building minimal Docker images with Nix. The below is a simple example taken from that blog post, modified to support Nix 2.0:

{ pkgs ? import <nixpkgs> {} }:

with pkgs;
dockerTools.buildImage {
  name = "redis";
  runAsRoot = ''
    groupadd -r redis
    useradd -r -g redis -d /data -M redis
    mkdir /data
    chown redis:redis /data

  config = {
    Cmd = [ "${gosu.bin}/bin/gosu" "redis" "${redis}/bin/redis-server" ];
    ExposedPorts = {
      "6379/tcp" = {};
    WorkingDir = "/data";
    Volumes = {
      "/data" = {};

Using nix-linuxkit to have an x86_64-linux builder, this fails with an error about a bash executable which can't be run:

$ nix-build -j 1 --system x86_64-linux redis-small.nix
these derivations will be built:
building '/nix/store/jsydsrzs7h9pfnh8m6cxaysa9bafmp2z-redis-config.json.drv'...
/nix/store/6v88ick1cxnn5g91m8qrrqww0lrlr27x-bash-4.4-p23/bin/bash: /nix/store/6v88ick1cxnn5g91m8qrrqww0lrlr27x-bash-4.4-p23/bin/bash: cannot execute binary file
builder for '/nix/store/jsydsrzs7h9pfnh8m6cxaysa9bafmp2z-redis-config.json.drv' failed with exit code 126
cannot build derivation '/nix/store/pyx4q2wln2shlnjdp5ng43aqd6iba80d-docker-image-redis.tar.gz.drv': 1 dependencies couldn't be built
error: build of '/nix/store/pyx4q2wln2shlnjdp5ng43aqd6iba80d-docker-image-redis.tar.gz.drv' failed

The key line here is /nix/store/6v88ick1cxnn5g91m8qrrqww0lrlr27x-bash-4.4-p23/bin/bash: cannot execute binary file. Using file to inspect that, it's genuinely a Linux ELF binary.

Incidentally, the same thing also happens with the following one-liner, taken from an answer to StackOverflow question How to build a Docker container with Nix?, also using dockerTools:

$ nix-build -j 1 --system x86_64-linux -E 'with import <nixpkgs> {}; pkgs.dockerTools.buildImage { name = "nix-htop"; contents = pkgs.htop; config = { Cmd = [ "/bin/htop" ]; }; }'

...fails similarly:

building path(s) ‘/nix/store/gz4lrsjcmxbcmdfpmazwz0wqnb5pbw8k-nix-htop-config.json’
/nix/store/nkq0n2m4shlbdvdq0qijib5zyzgmn0vq-bash-4.4-p12/bin/bash: /nix/store/nkq0n2m4shlbdvdq0qijib5zyzgmn0vq-bash-4.4-p12/bin/bash: cannot execute binary file
builder for ‘/nix/store/487mmw8kql56q7h6iq4c7hfzh4k0gv50-nix-htop-config.json.drv’ failed with exit code 126

Is dockerTools the common thread here?

  • I get the same error as you. Did you manage to get to the bottom of this Charles? Any workarounds? – groodt Jun 1 at 5:59
  • My recollection is that I switched from dockerTools to using a different toolchain, something using xhyve directly with Nix tooling maintained upstream, but I'm not using it any longer today and don't remember what it was. Apologies about that -- if I'd remembered asking this question, I would presumably have answered it at the time, when the solution was fresh in my head. – Charles Duffy Jun 1 at 14:52

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