A lot happens in the background when you upgrade Windows 10 to a new version. All of it is automated and of little interest to the user or admin unless something goes wrong.
If the worst case scenario happens, you end up with an unusable version of Windows 10 or the previous version of Windows if the rollback was successful.
Error codes may point you in the right direction, but more often than not it is essential to analyze log files that Windows creates during the upgrade process.
Windows would not be Windows if you'd simply have to open a single log file for the analysis. The upgrade process creates different logs depending on the state it is in and saves those logs into different locations on the hard drive on top of that.
The most important upgrade logs are setupact.log and setuperr.log which you find in different locations depending on the upgrade stage.
There are other logs that you may find useful as well. The following table lists log file names, locations, and descriptions:
|Log file name||Location||Description|
Microsoft suggests to use the logs in different situations.
The following table highlights the suggestions:
|Log file name||Location||Suggestions|
|setupact.log||$Windows.~BT\Sources\Panther||All down-level failures and rollback investigations|
|setupact.log||$Windows.~BT\Sources\Panther\UnattendGC||OOBE phase rollbacks, 0x4001C, 0x4001D, 0x4001E, 0x4001F|
|setupact.log||$Windows.~BT\Sources\Rollback||Generic rollbacks, 0xC1900101|
|setupact.log||Windows||Setup launch failures|
|setuperr.log||$Windows.~BT\Sources\Panther||Complete error listing|
|setuperr.log||$Windows.~BT\Sources\Panther\UnattendGC||Complete error listing|
|setuperr.log||$Windows.~BT\Sources\Rollback||Complete error listing|
|setuperr.log||Windows||Complete error listing|
|setuperr.log||Windows\Panther||Complete error listing|
|BlueBox.log||Windows\Logs\Mosetup||WSUS and WU down-level failures, 0xC1900107|
|setupapi.dev.log||$Windows.~BT\Sources\Rollback||Device install issues, 0x30018|
|*.evtx||$Windows.~BT\Sources\Rollback||Generic rollbacks, 0xC1900101|
The two important log files setupact.log and setuperr.log use the following format:
Microsoft suggests to look at SP (Setup Platform), MIG (Migration Engine) and CONX (Compatibility Information) entries in particular for troubleshooting issues.
Windows displays an error code (usually) when an upgrade or installation fails. Use the extend code of the error to identify the log file that you should look at.
Open the log file in question, and search for the error code that Windows Setup displayed on the screen.
Additional information about troubleshooting errors are available on the Microsoft Docs website.
Now You: How do you analyze upgrade errors on Windows?
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