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  1. C:
  2. $WINDOWS.~BT
  3. Sources\Panther
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Sources\Panther C:\$WINDOWS.~BT\Sources\Panther

Sources\Panther under $WINDOWS.~BT: setupact.log, setuperr.log and miglog.xml from the offline and rollback phases of a Windows upgrade.

Updated on By AltF4 Formation

What it’s for

Windows Setup logs from the offline (“Down-Level”) phase of an upgrade, before the new system is in place under C:\Windows. Read them first when an upgrade fails or rolls back, as long as $WINDOWS.~BT still exists.

What it contains

  • setupact.log: every Setup action, including the start of rollback operations.
  • setuperr.log: errors only, shorter to scan for the first code at fault (for example 0xC1900101 and its variants).
  • miglog.xml: user directory structure with SIDs.
  • The rollback phase also writes to the neighboring $WINDOWS.~BT\Sources\Rollback folder.

Risks and best practices

  • After a successful upgrade these logs are picked up under C:\Windows\Panther; after a failure they stay here. Copy the folder before running Disk Cleanup, which removes $WINDOWS.~BT.
  • Keep setupact.log and setuperr.log of the same attempt together: a second attempt overwrites or extends the content.

Useful commands

Fenêtre de terminal
# First Setup errors
Get-Content 'C:\$WINDOWS.~BT\Sources\Panther\setuperr.log' -TotalCount 30


# Upgrade failure codes in setupact.log
Select-String -Path 'C:\$WINDOWS.~BT\Sources\Panther\setupact.log' -Pattern '0xC1900|0x8007|Error' | Select-Object -First 30


# Backup copy before cleanup
Copy-Item 'C:\$WINDOWS.~BT\Sources\Panther' 'C:\Temp\Panther-backup' -Recurse

SetupDiag, a free Microsoft tool, reads these folders and summarizes the likely cause of the failure.

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