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  2. $WINDOWS.~BT
FolderRisk: Caution
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$WINDOWS.~BT C:\$WINDOWS.~BT

Hidden temporary folder created during a Windows upgrade: setup files, Panther logs and rollback data.

Updated on By AltF4 Formation

What it’s for

Windows creates $WINDOWS.~BT at the root of the system volume during an upgrade (for example to a new Windows 10 version or to Windows 11). It serves the offline phase of setup and keeps the logs of each phase. It is hidden by default.

What it contains

  • Sources\Panther: logs of the “Down-Level” phase (setupact.log, setuperr.log). Sources\Panther\UnattendGC covers the OOBE phase.
  • Sources\Rollback: rollback phase logs (setupact.log) and supplemental logs (setupapi.dev.log, .evtx event logs, Setupmem.dmp).
  • The setup files used by the offline phase.

Risks and best practices

  • Its logs are the reference for diagnosing an upgrade, so keep the folder while an upgrade is in progress and until you have analyzed a failure, and copy the logs before any cleanup.
  • Once the upgrade has succeeded and been validated, clean it up with Disk Cleanup (the temporary Windows installation files option) rather than by hand.
  • If deletion fails because of locked files, first check that no upgrade is pending.

Useful commands

Fenêtre de terminal
# Folder contents (hidden)
Get-ChildItem -Force 'C:\$WINDOWS.~BT' | Select-Object Mode, Name


# Last lines of the offline phase log
Get-Content 'C:\$WINDOWS.~BT\Sources\Panther\setupact.log' -Tail 50


# Installation errors
Select-String -Path 'C:\$WINDOWS.~BT\Sources\Panther\setuperr.log' -Pattern 'Error'

Folder contents

Folders 1

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