To create the gallery item package we have to use the Azure Gallery Packager. Run the following command:

    AzureGalleryPackager.exe -m <path to manifest.json file>
    -o <path to save the created package to>  

In order to create the .azpkg file perform the following steps:

1. Download the Azure Gallery Packager from http://aka.ms/azurestackmarketplaceitem.
2. Extract it, for example in the same folder as the JSON files are in C: emp.
3. Create a folder in C: emp with the name of UbuntuServer. If this folder does not exist next step will give you no results.

4. Open a PowerShell or Command Prompt to create the GalleryItemPackage and place it in the UbuntuServer folder. The path of the Manifest.json file was shown in the section Creating the Manifest.json file. Therefore enter the following:

      cd C:	emp
      .AzureGalleryPackageGeneratorAzureGalleryPackager.exe
      -m C:	empUbuntuServer16-04Manifest.json
      -o C:	empUbuntuServer

After the job finishes you should see the .azpkg file in the UbuntuServer folder. The name should be publisher.name.version.azpkg—in our case canonical.ubuntuserver16-04.1.0.0.azpkg.