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Published on July 2, 2018 by Microsoft

In this episode of Defrag Tools, we talk about the Windows Upgrade Log files.

The "Panther" logs track the installation of a Windows Upgrade. The logs contain Information, Warnings and Errors. Not all errors are fatal, the trick is to look at only the (last) fatal error if an upgrade fails.

The logs pre/post upgrade can be found in:

  • $Windows.~btsourcespanther
  • $Windows.~btSourcesRollback
  • WindowsPanther
  • WindowsPantherNewOS

You can review the logs manually, or use SetupDiag.

In the next episode, we’ll dive deep into the logs when there is an application migration issue.

Contact us at and/or @defragtools

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1 Comment on "Defrag Tools #193 – Windows Upgrade Logs"

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Philip Saunders
Philip Saunders
9 days 6 hours ago

If your on a line you can press shift and cursor down to highlight a line of text.