exportImage Inputs (cont.) and Examples

Because of this, using this function requires the `kvm` device to be available, see [`system-features`](https://nixos.org/manual/nix/stable/command-ref/conf-file.html#conf-system-features). ::: ### Inputs {#ssec-pkgs-dockerTools-exportImage-inputs} `exportImage` expects an argument with the following attributes: `fromImage` (Attribute Set or String) : The repository tarball of the image whose filesystem will be exported. It must be a valid Docker image, such as one exported by `docker image save`, or another image built with the `dockerTools` utility functions. If `name` is not specified, `fromImage` must be an Attribute Set corresponding to a derivation, i.e. it can't be a path to a tarball. If `name` is specified, `fromImage` can be either an Attribute Set corresponding to a derivation or simply a path to a tarball. See [](#ex-dockerTools-exportImage-naming) and [](#ex-dockerTools-exportImage-fromImagePath) to understand the connection between `fromImage`, `name`, and the name used for the output of `exportImage`. `fromImageName` (String or Null; _optional_) : Used to specify the image within the repository tarball in case it contains multiple images. A value of `null` means that `exportImage` will use the first image available in the repository. :::{.note} This must be used with `fromImageTag`. Using only `fromImageName` without `fromImageTag` will make `exportImage` use the first image available in the repository. ::: _Default value:_ `null`. `fromImageTag` (String or Null; _optional_) : Used to specify the image within the repository tarball in case it contains multiple images. A value of `null` means that `exportImage` will use the first image available in the repository. :::{.note} This must be used with `fromImageName`. Using only `fromImageTag` without `fromImageName` will make `exportImage` use the first image available in the repository ::: _Default value:_ `null`. `diskSize` (Number; _optional_) : Controls the disk size (in megabytes) of the VM used to unpack the image. _Default value:_ 1024. `name` (String; _optional_) : The name used for the output in the Nix store path. _Default value:_ the value of `fromImage.name`. ### Examples {#ssec-pkgs-dockerTools-exportImage-examples} :::{.example #ex-dockerTools-exportImage-hello} # Exporting a Docker image with `dockerTools.exportImage` This example first builds a layered image with [`dockerTools.buildLayeredImage`](#ssec-pkgs-dockerTools-buildLayeredImage), and then exports its filesystem with `dockerTools.exportImage`. ```nix { dockerTools, hello }: dockerTools.exportImage { name = "hello"; fromImage = dockerTools.buildLayeredImage { name = "hello"; contents = [ hello ]; }; } ``` When building the package above, we can see the layers of the Docker image being unpacked to produce the final output: ```shell $ nix-build (some output removed for clarity) Unpacking base image... From-image name or tag wasn't set. Reading the first ID. Unpacking layer 5731199219418f175d1580dbca05677e69144425b2d9ecb60f416cd57ca3ca42/layer.tar tar: Removing leading `/' from member names Unpacking layer e2897bf34bb78c4a65736510204282d9f7ca258ba048c183d665bd0f3d24c5ec/layer.tar tar: Removing leading `/' from member names Unpacking layer 420aa5876dca4128cd5256da7dea0948e30ef5971712f82601718cdb0a6b4cda/layer.tar tar: Removing leading `/' from member names Unpacking layer ea5f4e620e7906c8ecbc506b5e6f46420e68d4b842c3303260d5eb621b5942e5/layer.tar tar: Removing leading `/' from member names Unpacking layer 65807b9abe8ab753fa97da8fb74a21fcd4725cc51e1b679c7973c97acd47ebcf/layer.tar tar: Removing leading `/' from member names Unpacking layer b7da2076b60ebc0ea6824ef641978332b8ac908d47b2d07ff31b9cc362245605/layer.tar Executing post-mount steps... Packing raw image... [ 1.660036] reboot: Power down /nix/store/x6a5m7c6zdpqz1d8j7cnzpx9glzzvd2h-hello ``` The following command lists some of the contents of the output to verify that the structure of the archive is as expected:

This section continues the description of the `exportImage` function, detailing the remaining input attributes: `fromImageTag`, `diskSize`, and `name`. It provides a practical example demonstrating how to use `dockerTools.exportImage` in conjunction with `dockerTools.buildLayeredImage` to export the filesystem of a Docker image.