Windows Answer File Generator

The Answer File Generator is a command line application and library for generating answer files for unattended Windows installations. These files are commonly called unattend.xml or autounattend.xml (depending on the installation method used).

This tool can be used to generate answer files as part of an automated workflow for installing Windows, or just as a convenient way to generate answer files for personal use, without the need to install the Windows System Image Manager, or manually edit XML files.

Answer files can customize many aspects of the Windows installation, only some of which are available through this tool. Customizations supported by the Answer File Generator include:

• The installation method, partition layout, and target disk and partition.
• Enabling optional features during installation.
• Creation of local user accounts.
• Joining a domain and adding domain accounts to the local Administrators group.
• Configuring automatic log-on.
• The product key, computer name, language/culture, and time zone.
• Display resolution.
• Disabling Windows Defender.
• Enabling remote desktop access.
• Running PowerShell scripts and other commands on first log-on.

All of these items can be customized using command line arguments. In addition, the answer files generated here will always skip the entire OOBE experience unless no local account was created and no domain was joined.

Below, the core functionality is explained with several examples. You can also check the full list of command line arguments, or run ./GenerateAnswerFile -Help.

See what's new in Answer File Generator.

If you need additional customization, you will have to edit the generated answer file. If you'd like any other options to be available through the tool, you can file an issue or submit a pull request.

Installation method

The Answer File Generator supports several methods of installing Windows, which are specified using the -Install argument. The following values are supported.

Method	Description
PreInstalled	This is the default method, which is used to customize an already installed Windows image, such as one created using sysprep, or an image that was manually expanded using DISM tools such as Expand-WindowsImage. Some features are unavailable using this method, including installation of optional features.
CleanEfi	Performs a clean installation for systems using UEFI on the disk indicated by the -InstallToDisk argument. This disk will be repartitioned according to the -Partition argument, or using a default layout of a 100MB EFI partition, a 128MB MSR partition, and the remainder of the disk used for the OS installation.
CleanBios	Performs a clean installation for systems using legacy BIOS on the disk indicated by the -InstallToDisk argument. This disk will be repartitioned according to the -Partition argument, or using a default of a 100MB system partition, and the remainder of the disk used for the OS installation.
ExistingPartition	Installs Windows to an existing partition, specified using the -InstallToDisk and -InstallToPartition arguments. This partition will be formatted before installation, but other partitions are not touched. The system must already have a suitable system or EFI partition.
Manual	Allows the user to specify the target disk/partition during setup. When using this method, installation is not fully unattended and will require user intervention during the first stage.

The -InstallToDisk argument takes the zero-based disk index, in the order that the Windows installation (when executed manually) would list them. The -InstallToPartition argument is one-based instead (don't look at me; that's how the IDs work in the answer file).

Selecting the edition to install

Usually, Windows installation media contains multiple editions, such as Professional or Home, and you must select which edition to install. The most common way to do this is using the product key, which can be set using the -ProductKey argument. Setting the product key will select the correct edition to install, and activate Windows using that key. Setting a product key in the answer file is required for most installations of Windows unless the installation method is PreInstalled.

Versions of Windows that use alternative activation methods, such as volume licensing, do not require a product key in the answer file. In this case, if the installation media holds multiple editions, you can select the desired one using the -ImageIndex argument. You can use the Get-WindowsImage PowerShell command to list the images in an install.wim or install.esd file.

Passwords in answer files

Passwords are needed for several actions taken by the answer file. When creating local accounts, their initial password must be set. To join a domain, the password of a domain account with the appropriate permissions must be specified. For automatic log-on, you must specify the password of the account that will be logged on.

⚠️ Passwords in answer files are not securely stored ⚠️

They are at best base64-encoded (which is easily reversible), and at worst just stored in plain text. Do not store answer files with sensitive passwords in unsecure locations, and delete such files when you are done with them.

The answer file generator also does not treat these passwords securely (it can't, to be able to write them out to the answer file in this fashion), so copies of the passwords may remain in system memory after the application is terminated.

Time zone

The Answer File Generator defaults to Pacific Standard Time. To change this, use the -TimeZone argument. Run tzutil /l for a list of accepted time zone names.

Examples

To make them easier to read, the examples below are split over multiple lines, using the PowerShell syntax to continue a command on the next line.

Clean installation using UEFI

./GenerateAnswerFile autounattend.xml `
    -Install CleanEfi `
    -ProductKey ABCDE-12345-ABCDE-12345-ABCDE

The resulting answer file will install a 64 bit version of Windows on the first disk of a UEFI system, using the default UEFI partition layout, and activates it using the specified product key.

Installing a 32 bit OS

./GenerateAnswerFile autounattend.xml `
    -Install CleanBios `
    -ProcessorArchitecture x86 `
    -ProductKey ABCDE-12345-ABCDE-12345-ABCDE

By default, the generated answer files are for Windows editions running on 64 bit Intel or AMD processors. Use the -ProcessorArchitecture argument to specify a different CPU architecture, such as "x86" for 32 bit processors, or "arm64" for ARM based systems.

Creating a user during installation

./GenerateAnswerFile autounattend.xml `
    -Install CleanEfi `
    -LocalAccount "John,Password" "Steve,OtherPassword" `
    -ProductKey ABCDE-12345-ABCDE-12345-ABCDE

This example creates a user named "John" with the password "Password" (don't use that as your password, obviously), and a user named "Steve" with the password "OtherPassword". The -LocalAccount argument takes one or more values, allowing the creation of any number of accounts.

All accounts created during this method will be members of the local Administrators group.

Joining a domain and automatic log-on

./GenerateAnswerFile unattend.xml `
    -ComputerName mypc `
    -JoinDomain mydomain `
    -JoinDomainUser domainuser `
    -JoinDomainPassword Password `
    -DomainAccount domainuser `
    -AutoLogonUser mydomain\domainuser `
    -AutoLogonPassword Password

The answer file created by this command sets the computer name to "mypc" and joins it to the domain "mydomain", using the supplied credentials. It also adds the account "domainuser" from the "mydomain" domain to the local Administrators group, and logs in using that account automatically on first boot.

This sample does not use the -Install argument, so it creates an answer file suitable for pre-installed Windows images, such as those created using sysprep or DISM tools. The -JoinDomain argument can be used with any install method, however.

The -AutoLogonUser argument can be used for both domain or local accounts; to use a local account, specify the user name only, without a domain. To log in automatically more than once, use the -AutoLogonCount argument¹.

Custom partition layout

If you use the CleanEfi or CleanBios, you can choose to customize the partition layout for the disk specified by -InstallToDisk, by using the -Partition argument. This argument accepts multiple values, each creating a partition on that disk in the order specified.

If the -Partition argument is not specified, the default partition layout for the install method is used, as specified in the table above.

The -Partition argument uses the format label:size, where label is the volume label, and size is the size of the partition. The size can use multiple-byte units, such as GB or MB², and will be rounded down to a whole number of megabytes. If the size is *, it indicates the partition will fill the remainder of the disk.

./GenerateAnswerFile autounattend.xml `
    -Install CleanEFI `
    -ProductKey ABCDE-12345-ABCDE-12345-ABCDE `
    -Partition System:100MB MSR:128MB Windows:256GB Data:*

This example creates four partitions: a 100 MB EFI partition, a 128 MB Microsoft Reserved partition, a 256 GB partition that the OS will be installed to, and an additional partition that fills the remainder of the disk.

Several values for the volume label are used to create special partition types.

Label	Meaning
System	For CleanEfi, creates the EFI system partition (ESP). For CleanBios, creates the system partition holding the Windows boot manager.
MSR	Creates a partition with the Microsoft Reserved partition type. For use with CleanEfi only.
WinRE or Recovery	Marks the partition as a utility partition.

These special partition types will not have a drive letter. All other volume labels create regular data partitions with that label. These will be assigned drive letters in the order they were specified, starting with C:.

You can use the format label:size[fs], where fs is a file system like FAT32 or NTFS, to specify a file system to format the volume with. If no file system is specified, it defaults to NTFS except for EFI partitions, which must be FAT32. MSR partitions are not formatted, so this attribute is ignored.

You can use the -InstallToPartition argument to specify which partition should hold the OS. If you don't supply this argument, Windows will be installed on the first regular data partition.

If you use CleanBios and specify more than four partitions, the Answer File Generator will create an answer file that creates an extended partition, and creates the remaining partitions as logical volumes in that partition.

Optional features

Answer files can be used to enable optional features during installation. To do this, use the -Feature argument. This argument can take multiple values to enable multiple features.

./GenerateAnswerFile autounattend.xml `
    -Install CleanEfi `
    -Feature Microsoft-Windows-Subsystem-Linux VirtualMachinePlatform `
    -WindowsVersion 10.0.22621.1

This example enables the Windows Subsystem for Linux feature, and the Virtual Machine Platform feature.

When using optional features, the answer file must contain the exact version number of the Windows version being installed, such as "10.0.22621.1" (this is the version for Windows 11 22h2). You must specify this version using the -WindowsVersion argument. To find out the exact version number, the easiest way is to look at the file properties of the setup.exe file on your Windows installation media. The Windows version is not needed if you don't enable any optional features.

To determine the names of available optional features, you can use the Get-WindowsOptionalFeature PowerShell command.

You cannot specify optional features when using the PreInstalled method, as this is not supported by unattended installations. Optional features for a pre-installed image must be enabled prior to using sysprep, or by using DISM tools.

First log-on commands and scripts

./GenerateAnswerFile autounattend.xml `
    -Install CleanEfi `
    -FirstLogonCommand "reg add HKCU\Software\MyCompany /v ImportantRegistryKey /t REG_DWORD /d 1 /f" `
    -SetupScript "\\server\share\script.ps1 -Argument" `
    -LocalAccount "John,Password" `
    -AutoLogonUser John `
    -AutoLogonPassword Password `
    -ProductKey ABCDE-12345-ABCDE-12345-ABCDE

The -FirstLogonCommand argument can be used to execute a command when a user first logs on to the system after installation (either manually, or automatically as in the above example). For convenience, there is also a -SetupScript argument which executes the specified Windows PowerShell script, including any arguments.

Either argument accepts multiple values to run multiple commands or scripts. Both are executed in the order they are supplied, but all commands will be executed before any scripts.

If you execute any scripts, they must be stored in a location that is accessible to the system after installation, such as a network share like the example above.

Using an answer file

Please refer to the official Microsoft documentation to see how to use an answer file during Windows setup.

Ookii.AnswerFile library

The core functionality for generating answer files is implemented in the Ookii.AnswerFile library, which you can use in your own applications targeting .Net 7.0 or later.

Building and testing

To build Answer File Generator, make sure you have the following installed:

• Microsoft .Net 7.0 SDK or later

To build the application, library, and tests, simply use the dotnet build command in the src directory. You can run the unit tests using dotnet test.

The class library documentation is generated using Sandcastle Help File Builder.

Disclaimer

The Answer File Generator will generate files that, when used to install Windows, can erase a disk or partition on your system without user intervention. I am not responsible for any loss of data or any other adverse effects caused by the use of answer files generated by this tool.

Footnotes

1. Windows has a known issue with the LogonCount element which causes it to be inaccurate. The Answer File Generator adjusts the count and uses a first log-on command if needed to ensure the -AutoLogonCount argument is accurate. ↩

2. All sizes use powers of two, so 1MB is 1,048,576 bytes. You can also use IEC units such as MiB or GiB, with the same meaning. ↩