# Reference Manual: disko

## Module Options

We are currently having issues being able to generate proper module option
documentation for our recursive disko types. However you can read the available
options [here](https://github.com/nix-community/disko/tree/master/lib/types).
Combined wit the
[examples](https://github.com/nix-community/disko/tree/master/example) this
hopefully gives you an overview.

## Command Line Options

```
Usage: ./disko [options] disk-config.nix
or ./disko [options] --flake github:somebody/somewhere#disk-config

With flakes, disk-config is discovered first under the .diskoConfigurations top level attribute
or else from the disko module of a NixOS configuration of that name under .nixosConfigurations.

Options:

* -m, --mode mode
  set the mode, either format, mount or disko
    format: create partition tables, zpools, lvms, raids and filesystems
    mount: mount the partition at the specified root-mountpoint
    disko: first unmount and destroy all filesystems on the disks we want to format, then run the create and mount mode
* -f, --flake uri
  fetch the disko config relative to this flake's root
* --arg name value
  pass value to nix-build. can be used to set disk-names for example
* --argstr name value
  pass value to nix-build as string
* --root-mountpoint /some/other/mnt
  where to mount the device tree (default: /mnt)
* --dry-run
  just show the path to the script instead of running it
* --no-deps
  avoid adding another dependency closure to an in-memory installer
    requires all necessary dependencies to be available in the environment
* --debug
  run with set -x
```

## Generating Disk Images with Secrets Included using Disko

Using Disko on NixOS allows you to efficiently create `.raw` VM images from a
system configuration. The generated image can be used as a VM or directly
written to a physical drive to create a bootable disk. Follow the steps below to
generate disk images:

### Generating the `.raw` VM Image

1. **Build the disko image script:** Replace `mySystem` in the command below with your
   specific system configuration name:
   ```console
   nix build .#nixosConfigurations.mySystem.config.system.build.diskoImagesScript
   ```
2. **Execute the result file:** Execute the generated result file. Running
   `./result --help` will output the available options:

   ```console
   ./result --help
   Usage: $script [options]

   Options:
   * --pre-format-files <src> <dst>
     copies the src to the dst on the VM, before disko is run
     This is useful to provide secrets like LUKS keys, or other files you need for formating
   * --post-format-files <src> <dst>
     copies the src to the dst on the finished image
     These end up in the images later and is useful if you want to add some extra stateful files
     They will have the same permissions but will be owned by root:root
   * --build-memory
     specify the ammount of memory that gets allocated to the build vm (in mb)
     This can be usefull if you want to build images with a more involed NixOS config
     By default the vm will get 1024M/1GB
   * --write-to-disk </dev/disk>
     use an actuall disk instead of writing to a file
     This only works if your conifg has only one disk specified
     There is no check if the specified path is actually a disk so you can also write to another file
   ```

### Additional Configuration

- For virtual drive use, define the image size in your Disko configuration:

  ```console
  disko.devices.disk.<drive>.imageSize = "32G"; # Set your preferred size
  ```

- If the `.raw` image size is not optimal, use `--write-to-disk` to write
  directly to a drive. This bypasses the `.raw` file generation, which saves on read/write operations
  and is suitable for single disk setups.

### Understanding the Image Generation Process

1. Files specified in `--pre-format-files` and `--post-format-files` are
   temporarily copied to `/tmp`.
2. Files are then moved to their respective locations in the VM both before and
   after the Disko partitioning script runs.
3. The NixOS installer is executed, having access only to `--post-format-files`.
4. Upon installer completion, the VM is shutdown, and the `.raw` disk files are
   moved to the local directory.

> **Note**: The auto-resizing feature is currently not available in Disko.
> Contributions for this feature are welcomed. Adjust the `imageSize`
> configuration to prevent issues related to file size and padding.

By following these instructions and understanding the process, you can smoothly
generate disk images with Disko for your NixOS system configurations.