nix-alien

Introduction

You are running nix/NixOS and have ever encountered the following problem?

$ ./bb
bash: ./bb: No such file or directory

Fear not, now there is nix-alien which will download necessary dependencies
for you.

$ ./nix-alien bb            --> Run the binary inside a FHS shell with all needed shared dependencies to execute the binary
$ ./nix-alien-ld bb         --> Spawns you inside a shell with NIX_LD_LIBRARY_PATH set to the needed dependencies, to be used with nix-ld
$ ./nix-alien-find-libs bb  --> Lists all libs needed for the binary

Usage (Flakes)

Assuming you have nix already installed:

$ nix-shell -p nixUnstable nix-index
$ nix-index # this will take a long time
$ nix run --experimental-features 'nix-command flakes' "github:thiagokokada/nix-alien" -- ~/myapp

This will run nix-alien on ~/myapp binary with a FHSUserEnv including all
shared library dependencies. The resulting default.nix file will be saved to
$XDG_CACHE_HOME/nix-alien/<path-uuid>/default.nix, making the next evaluation
faster. You can also pass --recreate flag to force the recreation of
default.nix file, and --destination to change where default.nix file will
be saved.

You can edit your /etc/nix/nix.conf or ~/.config/nix/nix.conf file and
add the following line to avoid having to pass --experimental-features flag
every time:

experimental-features = nix-command flakes

From here on this guide will assume the above configuration is done for brevity.

To pass arguments to the app:

$ nix run "github:thiagokokada/nix-alien" -- ~/myapp -- --help

In case you’re using nix-ld, there is also
nix-alien-ld:

$ nix run "github:thiagokokada/nix-alien#nix-alien-ld" -- ~/myapp

This will spawn a mkShell instead with NIX_LD_LIBRARY_PATH and NIX_LD
setup. The resulting shell.nix file will be saved to
$XDG_CACHE_HOME/nix-alien/<path-uuid>/shell.nix, making the next evaluation
faster. You can also pass --recreate flag to force the recreation of
shell.nix file, and --destination to change where shell.nix file will
be saved.

If you want to use the fzf based menu to find the libraries for scripting
purposes, you can run:

$ nix run "github:thiagokokada/nix-alien#nix-alien-find-libs" -- ~/myapp

This will print the found libraries on the stdout. The informational messages
are printed to stderr, so you can easily redirect them to /dev/null if
needed. You can also use --json flag to print the result as a JSON instead.

To avoid the slow startup of nix-index, you can also download a pre-computed
index from nix-index-database:

$ nix run "github:thiagokokada/nix-alien#nix-index-update"

Usage (non-Flakes)

$ $(nix-build default.nix --no-out-link)/bin/nix-alien ~/myapp -- --arg foo
$ $(nix-build default.nix --no-out-link)/bin/nix-alien-ld ~/myapp
$ $(nix-build default.nix --no-out-link)/bin/nix-alien-find-libs ~/myapp
$ $(nix-build nix-index-update.nix --no-out-link)/bin/nix-index-update

Installation (Flakes)

{
  description = "nix-alien-on-nixos";

  inputs.nix-alien.url = "github:thiagokokada/nix-alien";
  inputs.nixpkgs.url = "github:NixOS/nixpkgs";

  outputs = { self, nixpkgs, nix-alien }: {
      nixosConfigurations.nix-alien-desktop = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      specialArgs = { inherit self; };
      modules = [
        ({ self, ... }: {
          nixpkgs.overlays = [
            self.inputs.nix-alien.overlay
          ];
          environment.systemPackages = with pkgs; [
            nix-alien
            nix-index # not necessary, but recommended
            nix-index-update
          ];
        })
      ];
    };
  };
}

Installation (non-Flakes)

{ pkgs, ... }:

let
  nix-alien-src = fetchTarball "https://github.com/thiagokokada/nix-alien/tarball/master";
  nix-alien = import (nix-alien-src) { };
  nix-index-update = import (nix-alien-src + "/nix-index-update.nix") {};
in
{
  environment.systemPackages = with pkgs; [
    nix-alien
    nix-index # not necessary, but recommended
    nix-index-update
  ];
}

Limitations

Binaries loading shared libraries dynamically (e.g.: with dlopen) will
probably not work with this script. However, this script can still be useful to
create an initial default.nix or shell.nix, that can be populated later with
the runtime dependencies of the program.

Technical Description

This is achieved by enumerating the shared library dependencies from the ELF
header using ldd (actually,
pylddwrap) and then searching for the
equivalent library in nixpkgs. This is done by querying nix-locate locally.
To solve possible conflicts, human intervation is needed, but thanks to
fzf and
pyfzf this is made easy by showing an
interactive list.

To be able to use nix-locate, first, the index has to be build. This is done
by running nix-index and waiting 10-15 minutes. To speed-up this process, this
repo also includes nix-index-update script, that downloads the index from
nix-index-database.