[](#ex-dockerTools-helpers-buildImage) and [](#ex-dockerTools-helpers-buildLayeredImage) show how to include these packages on `dockerTools` functions that build an image.
For more details on how that works, see the documentation for the function you're using.

### usrBinEnv {#sssec-pkgs-dockerTools-helpers-usrBinEnv}

This provides the `env` utility at `/usr/bin/env`.
This is currently implemented by linking to the `env` binary from the `coreutils` package, but is considered an implementation detail that could change in the future.

### binSh {#sssec-pkgs-dockerTools-helpers-binSh}

This provides a `/bin/sh` link to the `bash` binary from the `bashInteractive` package.
Because of this, it supports cases such as running a command interactively in a container (for example by running `docker container run -it <image_name>`).

### caCertificates {#sssec-pkgs-dockerTools-helpers-caCertificates}

This adds trusted root TLS/SSL certificates from the `cacert` package in multiple locations in an attempt to be compatible with binaries built for multiple Linux distributions.
The locations currently used are:

- `/etc/ssl/certs/ca-bundle.crt`
- `/etc/ssl/certs/ca-certificates.crt`
- `/etc/pki/tls/certs/ca-bundle.crt`

[]{#ssec-pkgs-dockerTools-fakeNss}
### fakeNss {#sssec-pkgs-dockerTools-helpers-fakeNss}

This is a re-export of the `fakeNss` package from Nixpkgs.
See [](#sec-fakeNss).

### shadowSetup {#ssec-pkgs-dockerTools-shadowSetup}

This is a string containing a script that sets up files needed for [`shadow`](https://github.com/shadow-maint/shadow) to work (using the `shadow` package from Nixpkgs), and alters `PATH` to make all its utilities available in the same script.
It is intended to be used with other dockerTools functions in attributes that expect scripts.
After the script in `shadowSetup` runs, you'll then be able to add more commands that make use of the utilities in `shadow`, such as adding any extra users and/or groups.
See [](#ex-dockerTools-shadowSetup-buildImage) and [](#ex-dockerTools-shadowSetup-buildLayeredImage) to better understand how to use it.

`shadowSetup` achieves a result similar to [`fakeNss`](#sssec-pkgs-dockerTools-helpers-fakeNss), but only sets up a `root` user with different values for the home directory and the shell to use, in addition to setting up files for [PAM](https://en.wikipedia.org/wiki/Linux_PAM) and a {manpage}`login.defs(5)` file.

:::{.caution}
Using both `fakeNss` and `shadowSetup` at the same time will either cause your build to break or produce unexpected results.
Use either `fakeNss` or `shadowSetup` depending on your use case, but avoid using both.
:::

:::{.note}
When used with [`buildLayeredImage`](#ssec-pkgs-dockerTools-buildLayeredImage) or [`streamLayeredImage`](#ssec-pkgs-dockerTools-streamLayeredImage), you will have to set the `enableFakechroot` attribute to `true`, or else the script in `shadowSetup` won't run properly.
See [](#ex-dockerTools-shadowSetup-buildLayeredImage).
:::

### Examples {#ssec-pkgs-dockerTools-helpers-examples}

:::{.example #ex-dockerTools-helpers-buildImage}
# Using `dockerTools`'s environment helpers with `buildImage`

This example adds the [`binSh`](#sssec-pkgs-dockerTools-helpers-binSh) helper to a basic Docker image built with [`dockerTools.buildImage`](#ssec-pkgs-dockerTools-buildImage).
This helper makes it possible to enter a shell inside the container.
This is the `buildImage` equivalent of [](#ex-dockerTools-helpers-buildLayeredImage).

```nix
{ dockerTools, hello }:
dockerTools.buildImage {
  name = "env-helpers";
  tag = "latest";

  copyToRoot = [
    hello
    dockerTools.binSh
  ];
}
```

After building the image and loading it in Docker, we can create a container based on it and enter a shell inside the container.
This is made possible by `binSh`.

```shell
$ nix-build
(some output removed for clarity)
/nix/store/2p0i3i04cgjlk71hsn7ll4kxaxxiv4qg-docker-image-env-helpers.tar.gz
$ docker image load -i /nix/store/2p0i3i04cgjlk71hsn7ll4kxaxxiv4qg-docker-image-env-helpers.tar.gz