setup-python fails on self hosted runners where runner has no administrator permissions

[ckrueger1979]

Description:
Setup-python fails on self hosted runners where runner has no administrator permissions.
Throw "Error happened during Python installation"

Action version:
setup-python@v6.2.0

Platform:

• Ubuntu
• macOS
• Windows

Runner type:

• Hosted
• [ X Self-hosted

Repro steps:
use self hosted runner, give runner accounts no administrative permissions

Expected behavior:
Python installs

Actual behavior:
Python installation fails

Root cause is this code line:
"DefaultAllUsersTargetDir=$PythonArchPath InstallAllUsers=1 $Include_freethreaded"
specific InstallAllUsers=1

[mahabaleshwars]

Hi @ckrueger1979,
Thank you for creating this issue. We will investigate it and provide feedback as soon as we have some updates.

[priyagupta108]

Hello @ckrueger1979,
Thank you for reporting this!

By design, the action requires administrator privileges on Windows self-hosted runners to create the necessary directories and files when downloading and installing a new version of Python for the first time. If your runner is configured as a service, please ensure the service account has the appropriate write permissions.

For more details on configuring your Windows self-hosted runner correctly, please refer to the Windows section of the setup-python documentation.

[ckrueger1979]

You are completly wrong.
It's your choice to pass "InstallAllUsers=1" and it's not nessecary to use the installer at all.
You could also use "Windows embeddable package (64-bit)"

[priyagupta108]

@ckrueger1979,
Thank you for the feedback!

The use of InstallAllUsers=1 is intentional and by design. The action installs Python into the shared runner tool cache (RUNNER_TOOL_CACHE) using the DefaultAllUsersTargetDir argument. For the MSI installer to respect DefaultAllUsersTargetDir and install into that shared path, InstallAllUsers=1 is required. Without it, the installer ignores DefaultAllUsersTargetDir entirely and falls back to a per-user path (%APPDATA%), which would break the tool cache mechanism.

Regarding the Windows embeddable package, while it is a valid lightweight option, it is intentionally minimal and does not suit the action's requirements:

• It does not include pip by default
• It has limited standard library support
• It does not integrate with the Windows registry

The action is designed to provide a full, consistent Python environment across all platforms. The Windows embeddable package, while technically workable with additional configuration, was not designed for this purpose and would require significant extra setup to match the same experience.

Hope this clarifies!

[ckrueger1979]

The parameter is DefaultJustForMeTargetDir instead of DefaultAllUsersTargetDir

[priyagupta108]

@ckrueger1979,
DefaultJustForMeTargetDir and DefaultAllUsersTargetDir are not interchangeable. They are paired with their respective installation mode: InstallAllUsers=1 uses DefaultAllUsersTargetDir, and InstallAllUsers=0 uses DefaultJustForMeTargetDir. As explained in my previous comment, the action uses InstallAllUsers=1 with DefaultAllUsersTargetDir intentionally and by design to support the shared tool cache mechanism.

Could you clarify what specific change you're proposing to the installer arguments?

[ckrueger1979]

It's no problem to install as user into the tool cache ...

[priyagupta108]

Hi @ckrueger1979 ,
Thank you for the suggestion! We will investigate this further and see if switching to InstallAllUsers=0 with DefaultJustForMeTargetDir is viable for our use case. However, the current InstallAllUsers=1 approach ensures system-wide visibility and predictable toolcache behavior across all runner contexts. We will consider this as a potential feature request for future improvements. In the meantime, please feel free to provide any additional details or suggestions you may have.