# Create the Setup Script for the VHD in Amazon WorkSpaces Applications
WorkSpaces Applications uses a setup script that you provide to mount the VHD before the application launches. You can also use the setup script to complete other tasks required to make your application work. For example, you can configure registry keys, register DLLs, manage pre-requisites, or modify the user profile from the setup script. WorkSpaces Applications provides script examples that you can use to mount your VHD. You will need to modify these scripts for your VHD and application needs.
**Note**
Setup scripts aren't required for app blocks with WorkSpaces Applications packaging. However, you can provide optional post-setup scripts to customize application installation.
Use the following links to download the example scripts:
+ [Ubuntu Pro 24.04 LTS bash script](samples/Linux-mount-vhd-script2.zip)
+ [Microsoft Windows Powershell script](samples/Windows-mount-vhd-script3.zip)
**Note**
WorkSpaces Applications and the Microsoft Windows operating system reserve drive letters A through E. Don't mount VHDs or network shares to these drive letters.
WorkSpaces Applications downloads the setup script and VHD to a directory on the fleet streaming instance, then runs the setup script. The setup script runs on the operating system with full administrator rights. The setup script runs in the `SYSTEM` context on Microsoft Windows, and as the `root` user on Ubuntu Pro 24.04 LTS.
File system location for the VHD and setup script:
+ Ubuntu Pro 24.04 LTS:
`/opt/appstream/AppBlocks/appblock-name/`
**`appblock-name` **
The name of the app block that the VHD and setup script correspond to.
+ Microsoft Windows:
`C:\AppStream\AppBlocks\appblock-name\`
**`appblock-name` **
The name of the app block that the VHD and setup script correspond to.
WorkSpaces Applications maintains the file name as they are on the object. For example, if your app block is named `MyApps`, with a VHD named `apps.vhd` and setup script named `mount-apps.ps1`, then the full path on a Windows streaming instance is:
+ VHD
`C:\AppStream\AppBlocks\MyApps\apps.vhd`
+ Setup script
`C:\AppStream\AppBlocks\MyApps\mount-apps.ps1`
WorkSpaces Applications captures the standard error and standard output from your setup script when it runs on a fleet streaming instance and uploads the output to an Amazon S3 bucket within your account. You can use these logs to identify and resolve issues you may have with your setup script. The buckets are named in a specific format as follows:
```
appstream-logs-region-code-account-id-without-hyphens-random-identifier
```
**`region-code` **
This is the AWS Region code in which the elastic fleet is created within.
**`account-id-without-hyphens` **
Your AWS account identifier. The random ID ensures that there is no conflict with other buckets in that Region. The first part of the bucket name, appstream-logs, does not change across accounts or Regions.
For example, if you create an elastic fleet in the US West (Oregon) Region (us-west-2) on account number 123456789012, WorkSpaces Applications creates an Amazon S3 bucket within your account in that Region with the name shown. Only an administrator with sufficient permissions can delete this bucket.
```
appstream-logs-us-west-2-1234567890123-abcdefg
```
The path for the folder where the log files are stored in the S3 bucket in your account uses the following structure:
```
bucket-name/fleet-name/instance-id/appblock-name/
```
**`bucket-name` **
The name of the Amazon S3 bucket in which the setup script logs are stored. The name format is described earlier in this section.
**`Instance-id` **
The unique identifier for the streaming instance that the setup script ran on
**`appblock-name` **
The name of the appblock that the setup script corresponds to.
The following example folder structure applies to a streaming session started from `test-fleet`. The session is from an AWS account ID of 123456789012, and appblock name is testappblock in the US West (Oregon) Region (us-west-2):
`appstream-logs-us-west-2-1234567890123-abcdefg/test-fleet/i-084427ab4a1cff7f5/testappblock/`
This example folder structure contains one log file for the standard output, and one log file for the standard error.
**Topics**
+ [App block setup script execution in Amazon WorkSpaces Applications](script-execution.md)
# App block setup script execution in Amazon WorkSpaces Applications
The following diagrams indicate where in the process the setup script runs. The run order is dependent upon whether Application Settings Persistence is enabled on the stack associated with the elastic fleet.
**Note**
WorkSpaces Applications uses your VPC details to download the VHD and setup script from the Amazon S3 bucket. Your VPC must provide access to the Amazon S3 bucket. For more information, see [Using Amazon S3 VPC Endpoints for WorkSpaces Applications Features](managing-network-vpce-iam-policy.md).
Application Settings Persistence is enabled:
![\[Application Settings Persistence is enabled.\]](http://docs.aws.amazon.com/appstream2/latest/developerguide/images/app-settings-enabled.png)
Application Settings Persistence is disabled:
![\[Application Settings Persistence is disabled.\]](http://docs.aws.amazon.com/appstream2/latest/developerguide/images/app-settings-disabled.png)