doc: assign ids to many headings

Building software with Nix often requires downloading source code and other files from the internet.

`nixpkgs` provides *fetchers* for different protocols and services. Fetchers are functions that simplify downloading files.

## Caveats

## Caveats {#chap-pkgs-fetchers-caveats}

Fetchers create [fixed output derivations](https://nixos.org/manual/nix/stable/#fixed-output-drvs) from downloaded files.

Nix can reuse the downloaded files via the hash of the resulting derivation.

Note that this function is meant for advanced use-cases. The more idiomatic way to work with flat-file binary caches is via the [nix-copy-closure](https://nixos.org/manual/nix/stable/command-ref/nix-copy-closure.html) command. You may also want to consider [dockerTools](#sec-pkgs-dockerTools) for your containerization needs.

## Example

## Example {#sec-pkgs-binary-cache-example}

The following derivation will construct a flat-file binary cache containing the closure of `hello`.

The behavior doesn't match `nix-shell` or `nix-build` exactly and this function is known not to work correctly for e.g. fixed-output derivations, content-addressed derivations, impure derivations and other special types of derivations.

:::

### Arguments

### Arguments {#ssec-pkgs-dockerTools-buildNixShellImage-arguments}

`drv`

    *Default:* (none)

### Example

### Example {#ssec-pkgs-dockerTools-buildNixShellImage-example}

The following shows how to build the `pkgs.hello` package inside a Docker container built with `buildNixShellImage`.

NixOS tests also use this function when preparing the VM. The `cptofs` method is used when `virtualisation.useBootLoader` is false (the default). Otherwise the second method is used.

## Features

## Features {#sec-make-disk-image-features}

For reference, read the function signature source code for documentation on arguments: <https://github.com/NixOS/nixpkgs/blob/master/nixos/lib/make-disk-image.nix>.

Features are separated in various sections depending on if you opt for a Nix-store only image or a full NixOS image.

### Common

### Common {#sec-make-disk-image-features-common}

- arbitrary NixOS configuration

- automatic or bound disk size: `diskSize` parameter, `additionalSpace` can be set when `diskSize` is `auto` to add a constant of disk space

- the current nixpkgs can be realized as a channel in the disk image, which will change the hash of the image when the sources are updated

- additional store paths can be provided through `additionalPaths`

### Full NixOS image

### Full NixOS image {#sec-make-disk-image-features-full-image}

- arbitrary contents with permissions can be placed in the target filesystem using `contents`

- a `/etc/nixpkgs/nixos/configuration.nix` can be provided through `configFile`

- EFI variables can be mutated during image production and the result is exposed in `$out`

- boot partition size when partition table is `efi` or `hybrid`

### On bit-to-bit reproducibility

### On bit-to-bit reproducibility {#sec-make-disk-image-features-reproducibility}

Images are **NOT** deterministic, please do not hesitate to try to fix this, source of determinisms are (not exhaustive) :

A `deterministic` flag is available for best efforts determinism.

## Usage

## Usage {#sec-make-disk-image-usage}

To produce a Nix-store only image:

```nix

} ./script.sh

```

#### setup hook that depends on the hello package and runs hello and @shell@ is substituted with path to bash

#### setup hook that depends on the hello package and runs hello and @shell@ is substituted with path to bash {#sec-pkgs.makeSetupHook-usage-example}

```nix

pkgs.makeSetupHook {

'')

```

## Attributes

## Attributes {#sec-pkgs.makeSetupHook-attributes}

* `name` Set the name of the hook.

* `propagatedBuildInputs` Runtime dependencies (such as binaries) of the hook.