The userdata is the user custom content exposed to the guest instance by the currently deployed and running cloud infrastructure. Its purpose is to provide additional data for the instance to customize it as much as you need, if the cloud initialization service does support this feature.

Fortunately, cloudbase-init is able to interpret and use this kind of user specific data in multiple ways. In most of the cases, the thing that indicates of what type is the processed data is usually the first line.

Currently supported contents:

PEM certificate


This one should start with a PEM specific beginning header, which will be eventually parsed by the configuration drive and web API OpenStack services and used by the WinRM certificate (main) plugin for storing and using it.


rem cmd

The file is executed in a cmd.exe shell (can be changed with the COMSPEC environment variable).


#ps1_sysnative (system native)

#ps1_x86 (Windows On Windows 32bit)

Execute PowerShell scripts using the desired executable. For finding out more about the system nativeness thing, click here.



A bash shell needs to be installed in the system and available in the PATH in order to use this feature.


#!/usr/bin/env python

Python is available by default with the build itself, but also it must be in the system PATH.

EC2 format

There is no “first line” here, but the content should follow a XML pattern with valid Batch/PowerShell script contents under script or powershell enclosing tags like in this example:

set root=%SystemDrive%
echo ec2dir>%root%\ec2file.txt

$root = $env:SystemDrive
$dname = Get-Content "$root\ec2file.txt"
New-Item -path "$root\$dname" -type directory

Cloud config


Cloud-config YAML configuration as supported by cloud-init, excluding Linux specific content. The following cloud-config directives are supported:

  • write_files - Defines a set of files which will be created on the local filesystem. It can be a list of items or only one item, with the following attributes:

    1. path - Absolute path on disk where the content should be written.
    2. content - The content which will be written in the given file.
    3. permissions - Integer representing file permissions.
    4. encoding - The encoding of the data in content. Supported encodings are: b64, base64 for base64-encoded content, gz, gzip for gzip encoded content, gz+b64, gz+base64, gzip+b64, gzip+base64 for base64 encoded gzip content.


    # One item
       encoding: b64
       content: NDI=
       path: C:\test
       permissions: '0o466'
    # Multiple items
       -   encoding: b64
           content: NDI=
           path: C:\b64
           permissions: '0644'
       -   encoding: base64
           content: NDI=
           path: C:\b64_1
           permissions: '0644'
       -   encoding: gzip
           content: !!binary |
           path: C:\gzip
           permissions: '0644'
  • set_timezone - Change the underlying timezone.


    set_timezone: Asia/Tbilisi
  • set_hostname - Override the already default set host name value. (metadata)


    set_hostname: newhostname

Multi-part content

MIME multi-part user data is supported. The content will ne handled based on the content type.

  • text/x-shellscript - Any script to be executed: PowerShell, Batch, Bash or Python.
  • text/part-handler - A script that can manage other content type parts. This is used in particular by Heat / CFN templates, although Linux specific.
  • text/x-cfninitdata - Heat / CFN content. Written to the path provided by heat_config_dir option which defaults to “C:\cfn”. (examples of Heat Windows templates)


When deciding which path to use for system executable files…

On 32bit OSes, the return value will be the System32 directory, which contains 32bit programs. On 64bit OSes, the return value may be different, depending on the Python bits and the sysnative parameter. If the Python interpreter is 32bit, the return value will be System32 (containing 32bit programs) if sysnative is set to False and Sysnative otherwise. But if the Python interpreter is 64bit and sysnative is False, the return value will be SysWOW64 and System32 for a True value of sysnative.

Why this behavior and what is the purpose of sysnative parameter?

On a 32bit OS the things are clear, there is one System32 directory containing 32bit applications and that’s all. On a 64bit OS, there’s a System32 directory containing 64bit applications and a compatibility one named SysWOW64 (WindowsOnWindows) containing the 32bit version of them. Depending on the Python interpreter’s bits, the sysnative flag will try to bring the appropriate version of the system directory, more exactly, the physical System32 or SysWOW64 found on disk. On a WOW case (32bit interpreter on 64bit OS), a return value of System32 will point to the physical SysWOW64 directory and a return value of Sysnative, which is consolidated by the existence of this alias, will point to the real physical System32 directory found on disk. If the OS is still 64bit and there is no WOW case (that means the interpreter is 64bit), the system native concept is out of discussion and each return value will point to the physical location it intends to.

On a 32bit OS the sysnative parameter has no meaning, but on a 64bit one, based on its value, it will provide a real/alias path pointing to system native applications if set to True (64bit programs) and to system compatibility applications if set to False (32bit programs). Its purpose is to provide the correct system paths by taking into account the Python interpreter bits too, because on a 32bit interpreter version, System32 is not the same with the System32 on a 64bit interpreter. Also, using a 64bit interpreter, the Sysnative alias will not work, but the sysnative parameter will take care to return SysWOW64 if you explicitly want 32bit applications, by setting it to False.